JP2021025049A - Sulfonated pulp fibers, derivative pulp, sulfonated fine cellulose fibers, method for making sulfonated fine cellulose fibers, and method for making sulfonated pulp fibers - Google Patents

Abstract

To provide a sulfonated pulp fiber, a derivative pulp, a sulfonated fine cellulose fiber, a method for producing a sulfonated fine cellulose fiber, and a method for producing a sulfonated pulp fiber.SOLUTION: The sulfonated pulp fiber of the present invention is a pulp fiber for a fine cellulose fiber used for increasing the viscosity of a dispersion, wherein the pulp fiber is a fiber whose part of hydroxy groups of the cellulose fiber are substituted with sulfo groups. The sulfonated pulp fiber has the amount of introduced sulfur due to the sulfo group of more than 0.42 mmol/g, and the water retention of the pulp fiber of 250% or more, while the sulfonated pulp fiber maintains the fiber shape. The hydroxy group at the C6 position of at least a part of the glucose unit constituting the cellulose fiber is substituted with a sulfo group. Since the sulfonated pulp fiber has a water retention ability of a predetermined value or more and predetermined hydroxy groups are substituted with sulfo groups while maintaining the fiber shape, the degree of freedom in handleability can be improved.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing a sulfonated pulp fiber, a derivative pulp, a sulfonated fine cellulose fiber, a sulfonated fine cellulose fiber, and a method for producing a sulfonated pulp fiber.

Cellulose nanofibers (CNFs) are fine fibers having a fiber width of several to several tens of nm and a fiber length of several hundred nm obtained by nano-treating plant-derived cellulose (mechanical defibration, TEMPO-catalyzed oxidation, etc.). .. Since CNF has light weight, high elasticity, high strength, and low linear thermal expansion, the use of composite materials containing CNF is expected not only in the industrial field but also in various fields such as the food field and the medical field. ing. Taking wood as an example, cellulose in wood forms a plant body by forming ultra-fine and highly crystalline microfibrils of about 3 nm in which 30 to 40 molecules of cellulose are bundled. Cellulose nanofibers, which are aggregates of cellulose fibers in which the structure of cellulose is maintained, can exhibit the above-mentioned characteristics. In particular, cellulose nanofiber materials having a fiber width as narrow as that of cellulose microfibrils are expected to be applied in various applications because they have characteristics of enormous specific surface area, high aspect ratio, and high transparency.

When the CNF is mechanically defibrated, a large amount of energy is required to obtain the CNF because the cellulose fibers are firmly bonded by hydrogen bonds. In addition, the obtained CNF has a problem that the fiber length and the like vary. Further, the fiber width of nanocellulose obtained by only mechanical defibration treatment such as a high-pressure homogenizer or a disc mill is several tens of nm at the minimum, no matter how many times the treatment is repeated. Therefore, there is also a problem that fibers having a fineness corresponding to microfibrils (about 3 nm in the case of wood) constituting plant fibers cannot be obtained, and characteristics such as high transparency and high aspect ratio cannot be exhibited.

Therefore, a manufacturing method has been developed in which a chemical treatment step is performed in which the cellulose fibers constituting the pulp are loosened to some extent before the mechanical defibration treatment step is performed (Patent Documents 1 to 4). By using this manufacturing method, CNF can be obtained with less energy than the manufacturing method in which pulp is directly machined. Moreover, there is an advantage that the variation in the size of the obtained CNF can be suppressed.

For example, Patent Documents 1 to 3 describe a manufacturing method in which pulp is chemically treated with a strong acid such as sulfuric acid, persulfuric acid, or a chlorine-based oxidizing agent, and then the obtained pulp slurry is supplied to a defibrator or the like to obtain CNF. Is disclosed.
However, in the production methods such as Patent Documents 1 to 3, since sulfuric acid, persulfuric acid, etc. are used in the chemical treatment process, in addition to the complexity of handling, the problem of wastewater treatment after the reaction and the corrosion of equipment piping and the like. There is a problem such as.
In addition, when a chlorine-based oxidant is used, there is concern about the impact of chlorine generated during the reaction on the environment. Furthermore, it is not clear whether the resulting nanocellulose has high transparency in the pulp after these pretreatments.

On the other hand, Patent Document 4 discloses a production method in which pulp is chemically treated with phosphate and urea, and then the obtained pulp slurry is supplied to a defibrator or the like to obtain CNF. By using such a production method, it is possible to solve the problem that occurs when a strong acid such as sulfuric acid is used in the chemical treatment step. Moreover, it is described that since the phosphoric acid ester can be introduced into a part of the hydroxyl groups on the surface of the obtained CNF, the dispersibility in an aqueous solvent can be improved.
Further, Patent Document 4 describes that a highly transparent CNF (with a haze value of 5 to 15%) can be produced by adjusting the solid content concentration to 0.2% by mass.

JP-A-2017-436777 JP-A-2017-8472 JP-A-2017-25240 Japanese Unexamined Patent Publication No. 2017-25468

However, in the technique of Patent Document 4, although there is a description regarding transparency, it is the case when the solid content concentration is 0.2% by mass. Further, Patent Document 4 does not have a specific description about the fiber length of the obtained CNF, and there is no specific description about the defibration property of the pulp after the chemical treatment. Furthermore, it is unclear in which part of the chemically treated pulp (cellulose or hemicellulose) the functional groups are mainly introduced. That is, for efficient derivatization of cellulose to obtain nanocellulose having the above characteristics (fine fiber width, high transparency), chemical modification to the surface of cellulose microfibrils, particularly chemical modification of the hydroxyl group at the C6 position However, Patent Document 4 has neither a description nor a suggestion regarding these.

In view of the above circumstances, the present invention provides sulfonated fine cellulose fibers having excellent transparency, sulfonated pulp fibers suitable for the sulfonated fine cellulose fibers, methods for producing these fibers, and derivative pulp containing such sulfonated pulp fibers. The purpose is to provide.

The sulfonated pulp fiber of the present invention is a pulp fiber for fine cellulose fibers used for increasing the viscosity of the dispersion liquid, and the pulp fiber is obtained by substituting a part of the hydroxyl groups of the cellulose fibers with sulfo groups. While maintaining the fiber shape, the amount of sulfur introduced due to the sulfo group is higher than 0.42 mmol / g, the water retention of the pulp fiber is 250% or more, and at least a part of the glucose constituting the cellulose fiber. The C6 position fiber of the unit is substituted with the sulfo group.
The sulfonated fine cellulose fiber of the present invention is a fine cellulose fiber in which the cellulose fiber is finely divided, and is for increasing the viscosity of the dispersion liquid in which the fine cellulose fiber is dispersed. A part of the hydroxyl group is substituted with a sulfo group, the amount of sulfur introduced due to the sulfo group is higher than 0.42 mmol / g, the average fiber width is 20 nm or less, and at least one constituting the cellulose fiber. The hydroxyl group at the C6 position of the glucose unit in the part was substituted with the above-mentioned sulfo group, and was dispersed in water at a solid content concentration of 0.5% by mass using a B-type viscometer at 20 ° C. The viscosity measured by rotating at 6 rpm for 3 minutes is 10,000 mPa · s or more.
The derivative pulp of the present invention is a pulp composed of a plurality of fibers, and the plurality of fibers are characterized by containing the sulfonated pulp fibers of the present invention.
The method for producing sulfonated pulp fiber of the present invention is a method for producing sulfonated pulp fiber in which the hydroxyl group at the C6 position of at least a part of the glucose units constituting the cellulose fiber is replaced with the sulfo group. A chemical treatment step of chemically treating is included, and the chemical treatment step includes a contact step of bringing the pulp fibers constituting the pulp into contact with a reaction solution prepared by dissolving sulfamic acid and urea in water, and the contact. The non-absolutely dry pulp after the step is supplied to the reaction step, and in the reaction step, a step of introducing a sulfo group into a part of the hydroxyl groups of the cellulose constituting the pulp fiber is carried out in order. The degree of polymerization of the obtained sulfonated pulp fiber includes a step of heating the pulp fiber in a state of contact with the reaction liquid after the contact step at a reaction temperature of 100 ° C. to 180 ° C. and a reaction time of 1 minute or more to proceed the reaction. The polymerization degree ratio before and after the reaction (polymerization degree after the reaction / polymerization degree before the reaction) is 50% or more.
In the method for producing sulfonated fine cellulose fibers of the present invention, a hydroxyl group at the C6 position of at least a part of glucose units constituting the cellulose fibers by subjecting a pulp containing a plurality of pulp fibers to a micronization treatment step is the sulfo group. A method for producing a substituted sulfonated fine cellulose fiber, wherein the plurality of pulp fibers include the sulfonated pulp fiber produced by the production method of the present invention, and in the micronization treatment step, the sulfonated pulp The step of finely dispersing the fiber-containing pulp in a water-soluble solvent so that the solid content concentration is 0.1% by mass to 20% by mass is included, and the degree of polymerization of the obtained sulfonated fine cellulose fiber is high. It is characterized in that the polymerization degree ratio before and after the miniaturization (polymerization degree after the miniaturization treatment / polymerization degree before the miniaturization treatment) is 85% or less.

According to the sulfonated pulp fiber of the present invention, the sulfo group has a water retention value of a predetermined value or more while maintaining the fiber shape, and the sulfo group is substituted with a predetermined hydroxyl group, so that the degree of freedom in handling is improved. Can be done.
According to the derivative pulp of the present invention, since the pulp fiber having a long average fiber length and a water retention degree of a predetermined value or more is contained, the degree of freedom in handleability can be improved.
According to the sulfonated fine cellulose fiber of the present invention, since the sulfo group is substituted with a predetermined hydroxyl group, the dispersibility and transparency in the state where the fine cellulose fiber is dispersed in the dispersion liquid can be improved.
According to the method for producing a sulfonated pulp fiber of the present invention, a sulfonated pulp fiber having excellent handleability is obtained by contacting a sulfonate having a sulfo group with a sulfone and / or a derivative thereof and reacting the pulp. Can be manufactured. Further, the sulfo group can be appropriately introduced into the hydroxyl group of the cellulose fiber even in a short reaction time.
According to the method for producing sulfonated fine cellulose fibers of the present invention, by contacting and reacting pulp with a sulfonate having a sulfo group and urea and / or a derivative thereof, appropriate fiber length and transparency can be obtained. It is possible to produce a sulfonated fine cellulose fiber having.

It is a schematic flow chart of the manufacturing method of the sulfonated fine cellulose fiber, the sulfonated pulp fiber and the derivative pulp of this embodiment. It is a graph showing the experimental results, and shows the amount of sulfur introduced and the degree of water retention. It is a graph which showed the experimental result and shows the degree of water retention. It is a graph which showed the experimental result, and shows the fiber length. It is a graph showing the experimental results and is related to reaction conditions (temperature and time). It is a graph showing the experimental results and is related to reaction conditions (temperature and time). It is a figure which showed the experimental result, and is the enlarged photograph of the fiber surface of the sulfamic acid / urea-treated pulp fiber corresponding to the sulfonated pulp fiber of this embodiment. It is a graph which showed the experimental result, and is related to the orientation strength of the sulfamic acid / urea-treated pulp fiber corresponding to the sulfonated pulp fiber of this embodiment. It is a figure which showed the experimental result, and is the enlarged photograph of the fiber surface of the sulfamic acid / urea-treated pulp fiber corresponding to the sulfonated pulp fiber of this embodiment. It is a figure which showed the experimental result, and is the figure which showed the defibration situation. It is a figure which showed the experimental result, and is the figure which showed the whiteness. It is a graph showing the experimental results and is related to transparency. It is a graph showing the experimental results and is related to transparency. It is a graph which showed the experimental result, and shows the degree of polymerization. It is a graph showing the experimental results, and shows the relationship between the degree of water retention and defibration. It is a graph showing the experimental results, and shows the relationship between the degree of water retention and defibration. It is a graph showing the experimental results, and shows the relationship between the degree of water retention and defibration. It is a graph showing the experimental results, and shows the relationship between the solid content concentration at the time of defibration and defibration. It is a figure which showed the experimental result, and is the figure which showed the measurement result of the FT-IR of the sulfamic acid / urea-treated pulp fiber corresponding to the sulfonated pulp fiber of this embodiment. It is a figure which showed the experimental result, and is the figure which showed the measurement result of the electric conductivity measurement of the nanocellulose fiber corresponding to the sulfonated fine cellulose fiber of this embodiment. It is a figure which showed the experimental result, and is the figure which showed the measurement result of the NMR measurement of the sulfamic acid / urea-treated pulp fiber corresponding to the sulfonated pulp fiber of this embodiment. It is a figure which showed the experimental result, and is the figure which showed the X-ray diffraction result of sulfamic acid / urea-treated pulp fiber corresponding to the sulfonated pulp fiber of this embodiment, and NBKP. It is a figure which showed the experimental result, and shows the X-ray diffraction result of the sulfamic acid / urea-treated pulp fiber corresponding to the sulfonated pulp fiber of this embodiment, and the nanocellulose fiber corresponding to the sulfonated fine cellulose fiber of this embodiment. It is a figure. It is a figure which showed the experimental result, and is the enlarged photograph of the surface of the nanocellulose fiber corresponding to the sulfonated fine cellulose fiber of this embodiment of this embodiment. It is a figure which showed the experimental result, and is the schematic explanatory view about the method of introducing the sulfo group into the C6 position.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The sulfonated pulp fiber and the derivative pulp of the present embodiment (hereinafter, each is simply referred to as a sulfonated pulp fiber and a derivative pulp) are characterized in that the handleability can be improved. In particular, the sulfonated pulp fiber and the derivative pulp are characterized in that the dispersion liquid obtained by dispersing the sulfonated fine cellulose fiber of the present embodiment in a liquid obtained by the micronization treatment has a high viscosity. There is.
The sulfonated fine cellulose fiber of the present embodiment (hereinafter, simply referred to as sulfonated fine cellulose fiber) is a fine cellulose fiber in which the cellulose fiber is finely divided, and the dispersion liquid dispersed in the liquid has excellent viscosity and transparency. It is characterized by having it.
The method for producing a sulfonated pulp fiber of the present embodiment (hereinafter referred to as a sulfonated pulp fiber manufacturing method) is characterized in that it enables the production of a sulfonated pulp fiber having excellent handleability. In particular, the sulfonated pulp fibers and derivative pulps obtained by the sulfonated pulp fiber manufacturing method are made so that the dispersion liquid in which the sulfonated fine cellulose fibers obtained by the micronization treatment is dispersed in a liquid has a high viscosity. It has characteristics.
In the method for producing sulfonated fine cellulose fibers of the present embodiment (hereinafter referred to as sulfonated fine cellulose fiber manufacturing method), the dispersion liquid dispersed in a liquid is excellent in viscosity and transparency, and sulfonated in which the entanglement between fibers is improved. It is characterized by making it possible to efficiently produce fine cellulose fibers. In particular, in the sulfonated fine cellulose fiber manufacturing method, fine cellulose fibers having desired properties can be easily and appropriately produced by refining the sulfonated pulp fibers produced by the sulfonated pulp fiber manufacturing method.

Hereinafter, embodiments of the sulfonated pulp fiber, the derivative pulp and the sulfonated fine cellulose fiber will be described first, and then the sulfonated pulp fiber manufacturing method and the sulfonated fine cellulose fiber manufacturing method will be described.

<Sulfonized pulp fiber>
The sulfonated pulp fiber is a pulp fiber composed of a plurality of cellulose fibers, and is a hydroxyl group (-) of cellulose (a chain polymer in which D-glucose is β (1 → 4) glycosidic bonded) constituting the cellulose fibers contained therein. At least a part of the OH group) is sulfonated with a sulfo group represented by the following formula (1). That is, in the sulfonated pulp fiber, a part of the hydroxyl groups of the cellulose fiber is replaced with a sulfo group.
Specifically, the sulfonated pulp fiber is such that the hydrophilicity of the fiber is improved by introducing a sulfo group.

(-SO3-) r · Zr + (1)
(Here, r is an independent natural number of 1 to 3, and Zr + is a group consisting of hydrogen ion, alkali metal cation, ammonium ion, aliphatic ammonium ion, and aromatic ammonium ion when r = 1. At least one selected from the group consisting of ammonium earth metal cations or polyvalent metal cations when r = 2 or 3).

Since the hydrophilicity of the sulfonated pulp fiber is considered to affect the amount of water that can be retained by the fiber, the amount of sulfo groups introduced into the sulfonated pulp fiber and the amount of sulfo group retained by the sulfonated pulp fiber may be retained. It is presumed that there is some relationship between the amount of water that can be produced (that is, the degree of water retention).

(Introduction amount of sulfo group in sulfonated pulp fiber)
The sulfonated pulp fiber is such that the hydrophilicity of the fiber is improved by introducing a sulfo group into the hydroxyl group of the glucose unit constituting the cellulose fiber as described above. That is, the sulfonated pulp fiber is made so that the dispersibility when dispersed in an aqueous solvent can be improved by introducing a sulfo group.

The amount of the sulfo group introduced into the sulfonated pulp fiber can be expressed by the amount of sulfur caused by the sulfo group, and is not particularly limited as long as the fiber can impart dispersibility in a long state. Specifically, in the sulfonated pulp fiber, the amount of the sulfo group introduced is adjusted so that the pulp fiber can be imparted with dispersibility and the average fiber length before replacing the pulp fiber with the sulfo group is 50% or more. You just have to.
For example, the amount of sulfur introduced due to the sulfo group per 1 g (mass) of the sulfonated pulp fiber is preferably adjusted to be higher than 0.1 mmol / g, more preferably 0.2 mmol / g to 9. It is 9.9 mmol / g, more preferably 0.42 mmol / g to 9.9 mmol / g.
As the amount of sulfur introduced due to the sulfo group per 1 g (mass) of the sulfonated pulp fiber approaches 9.9 mmol / g, there is a concern that the crystallinity may decrease, and the cost for introducing sulfur tends to increase.
Therefore, it is preferable to adjust the amount of the sulfo group introduced into the sulfonated pulp fiber, that is, the amount of sulfur introduced due to the sulfo group so as to be within the above range.

Since the number of sulfur atoms in the sulfo group is 1, the amount of sulfur introduced: the amount of sulfo group introduced = 1: 1 as in the case of the sulfonated fine cellulose fiber described later.

In particular, the amount of sulfo groups introduced into the sulfonated pulp fibers (the amount of sulfur introduced due to the sulfo groups) is 0.42 mmol / from the viewpoint of facilitating dispersal when the sulfonated pulp fibers are dispersed in an aqueous solvent. It is preferably adjusted to be higher than g, more preferably adjusted to 0.42 mmol / g to 9.9 mmol / g, and further preferably adjusted to be higher than 0.42 mmol / g and 3.0 mmol / g. Adjusted to be less than or equal to g, more preferably more than 0.42 mmol / g and less than 2.0 mmol / g, still more preferably higher than 0.42 mmol / g and 1.7 mmol / g. It is adjusted so as to be less than or equal to, more preferably higher than 0.42 mmol / g and not more than 1.5 mmol / g.
When the amount of sulfur introduced due to the sulfo group per 1 g (mass) of the sulfonated pulp fiber is 0.42 mmol / g or less, the state in which the fine fibers constituting the sulfonated pulp fiber are strongly bonded to each other is likely to be maintained.
Therefore, from the viewpoint of making the sulfonated pulp fiber easy to disperse, it is preferable to adjust the amount of the sulfo group introduced into the sulfonated pulp fiber, that is, the amount of sulfur introduced due to the sulfo group within the above range.

The lower limit of the amount of sulfo groups introduced in the sulfonated pulp fiber may be adjusted to be higher than 0.42 mmol / g. For example, it may be adjusted to 0.5 mmol / g or more, or may be adjusted to 0.6 mmol / g or more.

The term "fibers disintegrated" as used herein means a state in which a plurality of fine fibers constituting the sulfonated pulp fibers naturally disintegrate when the sulfonated pulp fibers are placed in an aqueous solvent. A state in which sulfonated pulp fibers can be made into a plurality of fine fibers by stirring with the force of.

(Method of measuring the amount of sulfo group introduced)
The amount of sulfo groups introduced into the sulfonated pulp fiber can be evaluated by the amount of sulfur introduced due to the sulfo groups. Specifically, it can be measured by using the same measuring method as in the case of the sulfonated fine cellulose fiber. That is, a predetermined amount of sulfonated pulp fiber can be burned, and the sulfur content contained in the combustible product can be measured by a method according to IEC 62321 using a combustion ion chromatograph.

(Water retention of sulfonated pulp fiber)
The sulfonated pulp fiber is also characterized in that it has a predetermined degree of water retention in addition to the amount of sulfur introduced due to the sulfo group described above. Specifically, the sulfonated pulp fiber is prepared so that the water retention degree of the sulfonated pulp fiber, that is, the amount of water contained after centrifugal dehydration is in a predetermined state.
The range of the water retention of the sulfonated pulp fiber is not particularly limited as long as it is appropriately adjusted according to the purpose of use and use described later.
For example, the water retention of the sulfonated pulp fiber is preferably adjusted to be 150% or more, more preferably higher than 200%, further preferably 220% or more, still more preferably 250%. Yes, more preferably 300% or more, and even more preferably 500% or more.

Here, if the water retention degree of the sulfonated pulp fiber is increased, the fiber will be in a state of containing a large amount of water. In such a state, it is presumed that the water content contained in the fibers affects the binding force between the fine fibers constituting the sulfonated pulp fibers.
That is, in the sulfonated pulp fiber prepared so as to have a high degree of water retention, the bond between the fine fibers constituting the surface of the sulfonated pulp fiber is weakened and a gap is formed between the adjacent fine fibers, and this is formed. It is presumed that the moisture is easily retained by the infiltration of moisture into the gaps.
Therefore, if the water retention level of the sulfonated pulp fiber is adjusted to be within the above range, the sulfonated pulp fiber can be prepared according to the following purposes and uses.

(From the viewpoint of dehydration)
For example, from the viewpoint of dehydration in the sulfonated pulp fiber, it may be prepared so that the amount of water in the fiber is small, that is, the degree of water retention is low.
By lowering the water retention level of the sulfonated pulp fiber, it is possible to suppress the transportation cost at the time of transportation, and the manufacturing efficiency and the manufacturing cost at the time of manufacturing the sulfonated pulp fiber can be suppressed.

(Viewpoint of miniaturization)
On the other hand, from the viewpoint of making the sulfonated pulp fiber finer (in other words, making it easier to loosen), it may be prepared so that the amount of water in the fiber is large, that is, the degree of water retention is high. For example, from the viewpoint of making the sulfonated pulp fiber easy to loosen (miniaturize), when the defibration pressure is 120 to 140 MPa, the water retention degree of the sulfonated pulp fiber may be adjusted to be higher than 150%. ..
The reason for this is that by increasing the water retention of the sulfonated pulp fibers, it is possible to weaken the binding force between the fine fibers constituting the sulfonated pulp fibers. Then, the surface of the sulfonated pulp fiber and the portion located inward near the surface are likely to be fibrillated. Then, if the sulfonated pulp fiber in such a state is provided in a defibrator or the like, the pulp fiber can be further miniaturized. That is, since it can be easily loosened when the sulfonated pulp fiber described later is miniaturized, it is considered that the workability and efficiency when preparing the sulfonated fine cellulose fiber described later can be improved.

In particular, as will be described in detail later, the fine cellulose fibers obtained by defibrating the sulfonated pulp fibers obtained by sulfonated the raw material pulp differ in the viscosity of the dispersion liquid in which the fine cellulose fibers are dispersed depending on the production method. Based on the finding that it occurs, in order to impart excellent viscosity to the dispersion, the sulfo group is preferentially introduced at the C6 position of the hydroxyl groups (C2, C3, C6) of the sulfonated pulp. By doing so, it is possible to provide a sulfonated pulp fiber having excellent defibration while maintaining the fiber shape, and to impart excellent viscosity to the dispersion liquid by defibrating the sulfonated pulp fiber. It is an object of the present invention to provide a sulfonated fine cellulose fiber capable.
That is, the sulfonated pulp fiber of the present embodiment has a configuration in which the amount of sulfur introduced is within the above range, the degree of water retention is equal to or higher than the above value, and the position where the sulfo group is introduced is preferentially C6. This is a pulp capable of improving defibration (fine treatment) and imparting high viscosity to a dispersion liquid in which sulfonated fine cellulose fibers obtained after defibration are dispersed.

When the sulfonated pulp fiber is refined, if the degree of water retention is too high, the concentration of the refined fiber tends to be too low or the yield tends to be low. Therefore, from the viewpoint of the yield and concentration of the fine fibers after the sulfonated pulp fibers are refined, it is preferable to adjust the water retention degree so as not to be too high. For example, the water retention degree is 10,000. It is preferable to adjust it so that it is less than%. Details will be described later.

Loosening the fibers in the specification means, for example, when defibrating a slurry of sulfonated pulp fibers, a plurality of fine fibers constituting the sulfonated pulp fibers are separated by applying energy to the sulfonated pulp fibers. It is something that makes you want to.

(Measurement method of water retention)
The water retention of the sulfonated pulp fiber can be determined by a general water retention test of the pulp fiber (for example, a method according to JAPAN TAPPI Pulp and Paper Test Method No. 26: 2000).

(Position of introduction of sulfo group in sulfonated pulp fiber)
As described above, the sulfonated pulp fiber is one in which a part of the hydroxyl groups of the glucose unit constituting the cellulose fiber is sulfonated by a sulfo group. The substitution position of the sulfo group is not particularly limited, but it is preferably prepared in a state in which the sulfo group is preferentially substituted with the hydroxyl group at the C6 position of the glucose unit (see FIG. 21). That is, in the sulfonated pulp fiber, the hydroxyl group at the C6 position of at least a part of the glucose units constituting the cellulose fiber is replaced with a sulfo group.

The hydroxyl group at the C6 position of this glucose unit is arranged so as to protrude three-dimensionally (see FIG. 21). Therefore, in the sulfonated pulp fiber, the sulfo group is preferentially introduced into the hydroxyl group at the C6 position arranged so as to protrude three-dimensionally in the glucose unit, so that the adjacent fibers (the sulfo group at the hydroxyl group at the C6 position) are preferentially introduced. Can generate a chargeable repulsive force between adjacent fibers having a introduced glucose unit.
Then, when the sulfonated pulp fiber is refined, in addition to the mechanical defibrating force, the chargeable repulsive force between the cellulose fibers constituting the sulfonated pulp fiber can be exerted. Compared with the one in which the sulfo group is introduced, the fiber can be made finer with a lower defibration pressure or the like. That is, the sulfonated pulp fiber (the sulfonated pulp fiber in which the sulfo group is preferentially substituted with the hydroxyl group at the C6 position of the glucose unit constituting the cellulose fiber) is prepared so as to have the above-mentioned high water retention. For example, at the time of defibration, it is possible to make defibration easier with less energy.

Since the sulfonated pulp fiber has a sulfo group at the C6 position, a sulfo group having a sulfo group introduced at the C6 position (that is, a sulfonated pulp having a sulfo group introduced at the C2 position or the C3 position, hereinafter the C2 position). And C3 position may be represented by C2-C3 position), and the fiber shape is significantly different.
Specifically, the sulfonated pulp fiber can be in a state where the fiber is less cut and broken as compared with the sulfonated pulp at the C2-C3 position. That is, the degree of polymerization can be maintained higher than that of the sulfonated pulp at the C2-C3 position.
Moreover, since the sulfonated pulp fiber has a sulfo group at the C6 position, the crystal region of the fiber can be maintained in a higher state than that of the sulfonated pulp at the C2-C3 position. That is, the crystallinity can be maintained higher than that of the sulfonated pulp at the C2-C3 position.
Further, since the sulfonated pulp fiber has a fiber shape having a high degree of polymerization and a high degree of crystallization by preferentially introducing a sulfo group at the C6 position as described above, it is refined by defibration or the like. The sulfonated fine cellulose fiber thus obtained can also exhibit excellent properties as compared with those in which the sulfo group is introduced at the C2 position and the C3 position. Specifically, it is possible to exhibit excellent viscosity with respect to the dispersion liquid in which the sulfonated fine cellulose fibers are dispersed in a solution.

The fact that the sulfo group is introduced into the hydroxyl group of the glucose unit described above means that the FT-IR measurement (see FIG. 19) and the electrical conductivity measurement (see FIG. 19) of the sulfonated fine cellulose fiber described later in which the sulfonated pulp fiber is micronized are measured. It can be confirmed by using (see FIG. 20), NMR measurement (see FIG. 21), and the like.
In particular, confirmation of the position of the hydroxyl group of the glucose unit in which the sulfo group is introduced can be confirmed by NMR measurement.

Further, the degree of polymerization and the degree of crystallinity of the sulfonated pulp fiber can be confirmed by the method described in Examples (see Table 21).

(Degree of polymerization of sulfonated pulp fiber)
The degree of polymerization of the sulfonated pulp fiber is particularly high if the fiber shape is maintained as described above, or if excellent viscosity can be imparted to the dispersion by defibrating the sulfonated pulp fiber. Not limited. For example, from the viewpoint of obtaining sulfonated fine cellulose fibers, it may be 350 or more. It is preferably 400 or more, more preferably 500 or more, and even more preferably 600 or more. On the other hand, from the viewpoint of handleability, for example, it is preferably 1000 or less, more preferably 900 or less, and further preferably 600 or less.

(Crystallinity of sulfonated pulp fiber)
The crystallinity of the sulfonated pulp fiber is such that the fiber shape is maintained as described above, or if excellent viscosity can be imparted to the dispersion liquid by defibrating the sulfonated pulp fiber. Not particularly limited. For example, from the viewpoint of obtaining sulfonated fine cellulose fibers, it is 70% or more, preferably 75% or more. On the other hand, from the viewpoint of handleability, for example, 90% or less is preferable, and 80% or less is more preferable.

(Average fiber length of sulfonated pulp fiber)
The length of the sulfonated pulp fiber is not particularly limited as long as the average fiber length is such that the fiber shape is maintained as described above.

Specifically, it suffices that the average fiber length maintains a predetermined length before and after sulfonation of the sulfonated pulp fiber. More specifically, when comparing the average fiber length of the pulp fiber before the introduction of the sulfo group into the sulfonated pulp fiber and the average fiber length of the sulfonated pulp fiber after the introduction of the sulfo group, the latter (that is, sulfone) The pulp fiber) is preferably prepared so as to be 50% or more, more preferably 70% or more, and further preferably 80% or more as compared with the former. In other words, the sulfonated pulp fiber is prepared so that the average fiber length becomes a predetermined value or more before and after the introduction of the sulfo group, regardless of the material of the pulp as a raw material.
For example, when wood-based pulp fiber is used as a raw material and the average fiber length is 2.6 mm, the average fiber length of the sulfonated pulp fiber is 50% or more of the average fiber length of the raw material pulp fiber. That is, it is adjusted to be 1.3 mm or more. Further, if the pulp fiber is LBKP described later and the average fiber length is about 1 mm, the pulp fiber is adjusted so that the average fiber width after sulfonated is about 0.5 mm or more.

If the average fiber length of the sulfonated pulp fiber is adjusted to be within the above range, the fiber can be made into a fiber having excellent handleability.
Specifically, it is possible to improve the entanglement of the fibers, homogenize the fibers to a desired length while maintaining a certain length, and when miniaturizing, the average of the fine fibers after miniaturization. Advantages such as being able to increase the fiber length can be obtained.
Therefore, it is possible to provide a sulfonated pulp fiber having an excellent degree of freedom according to the purpose of use and use.
On the other hand, when it is shorter than the above range, the influence when the sulfonated pulp fiber is hydrolyzed cannot be ignored, so that the degree of freedom tends to be limited.
Therefore, it is preferable to adjust the average fiber length of the sulfonated pulp fiber so as to be within the above range.

(Measuring method of average fiber length)
The average fiber length of the sulfonated pulp fiber can be measured using a known fiber analyzer. As a known fiber analyzer, for example, a fiber tester (manufactured by Lorenzen & Betley Co., Ltd.) can be mentioned.

As described above, by adjusting the introduction amount of the sulfo group of the sulfonated pulp fiber of the present embodiment, the dispersibility can be improved while maintaining the state where the fiber length is long, so that the degree of freedom in handleability is improved. You will be able to do it.
Moreover, it becomes possible to improve the ease of loosening of the fibers and the transparency of the fine cellulose fibers described later.
Further, by adjusting the water retention degree of the sulfonated pulp fiber of the present embodiment, it can be appropriately adjusted according to the purpose and use of the sulfonated pulp fiber as described above, so that the degree of freedom of handling is improved. Sulfonized pulp fibers can be provided.

(Whiteness)
The sulfonated pulp fibers are washed by dispersing a plurality of sulfonated pulp fibers in an aqueous solution, and then dried. It is preferable to adjust the whiteness when dried so as to be within a predetermined range.
For example, the sulfonated pulp fiber may be prepared so that the whiteness is 30% or more, and preferably 40% or more. When the whiteness is 30% or more, the coloring becomes inconspicuous, so that the handleability can be improved.

The whiteness of the sulfonated pulp fiber can be determined by using a known method. For example, it can be measured according to JIS P 8148: 2001 (paper, paperboard and pulp-ISO whiteness (diffuse blue light reflectance)).

<Derivative pulp>
The derivative pulp is a pulp composed of a plurality of fibers, and is a pulp fiber prepared so as to contain a plurality of the above-mentioned sulfonated pulp fibers. Specifically, by assembling a plurality of sulfonated pulp fibers produced by using the sulfonated pulp fiber manufacturing method, a derivative pulp containing pulp fibers having a sulfo group introduced can be obtained.
This derivative pulp may be an aggregate of only a plurality of sulfonated pulp fibers produced by the sulfonated pulp fiber manufacturing method, or fibers made of a material other than cellulose (for example, polyvinyl alcohol (PVA)) or , Synthetic fibers such as polyester, natural fibers such as wool, etc.), other pulp fibers, etc. may be contained.
It is preferable that the content of the plurality of sulfonated pulp fibers produced by the sulfonated pulp fiber manufacturing method is adjusted to be high because the same effect as that of the sulfonated pulp fiber described above can be easily exhibited.

<Sulfonized fine cellulose fiber>
The sulfonated fine cellulose fiber is a fine cellulose fiber obtained by refining the cellulose fiber, and is a hydroxyl group of cellulose (a chain polymer in which D-glucose is β (1 → 4) glycosidic bonded) constituting the fine cellulose fiber. At least a part of (-OH group) is sulfonated by the sulfo group represented by the above formula (1). That is, in the sulfonated fine cellulose fiber, a part of the hydroxyl groups of the fine cellulose fiber is replaced with a sulfo group.

By having a sulfo group, the sulfonated fine cellulose fiber can improve the hydrophilicity of the fiber. That is, by introducing the sulfo group into the sulfonated fine cellulose fiber, the dispersibility when the sulfonated fine cellulose fiber is dispersed in the dispersion liquid can be improved. Moreover, the electronic repulsion of the introduced sulfo group makes it easier to maintain the state of being dispersed in the dispersion liquid.

In addition, it becomes possible to impart a physiologically active action derived from a sulfo group to sulfonated fine cellulose fibers. For example, chondroitin sulfate, which is a type of sulfated polysaccharide known as a heparinoid, has hyalnonidase inhibitory activity and skin moisturizing effect, and is therefore applicable to xerosis, sebum deficiency, and atopic dermatitis. It is being considered. Since the sulfonated fine cellulose fiber is also a kind of natural polysaccharide, it can be used in the medical field based on the bioactive action based on the sulfo group.

The solvent of the dispersion liquid is not particularly limited as long as it is an aqueous solvent. That is, the solvent used in the dispersion may be a water-soluble solvent (water-soluble solvent). For example, in addition to water alone, alcohols, ketones, amines, carboxylic acids, ethers, amides, etc., and mixtures thereof. Etc. can be adopted.

Further, the sulfonated fine cellulose fiber may have other functional groups bonded to it, and in particular, it may contain a functional group (substituent) containing sulfur in addition to the sulfo group.
In the following description, a case where only a sulfo group is introduced into the hydroxyl group of the cellulose fiber constituting the sulfonated fine cellulose fiber will be described as a representative.

(Introduction amount of sulfo group in sulfonated fine cellulose fiber)
The amount of sulfo group introduced in the sulfonated fine cellulose fiber can be expressed by the amount of sulfur caused by the sulfo group, and the amount introduced is not particularly limited as long as transparency and dispersibility can be maintained to some extent.
For example, the amount of sulfur introduced due to the sulfo group per 1 g (mass) of the sulfonated fine cellulose fiber is preferably adjusted to be higher than 0.42 mmol / g, and more preferably 0.42 mmol / g to. It is 9.9 mmol / g, more preferably 0.5 mmol / g to 9.9 mmol / g, and even more preferably 0.6 mmol / g to 9.9 mmol / g.

Since the number of sulfur atoms in the sulfo group is 1, the amount of sulfur introduced: the amount of sulfo group introduced = 1: 1. For example, when the sulfur introduction per 1 g (mass) of the sulfonated fine cellulose fiber is 0.42 mmol / g, the amount of the sulfo group introduced is naturally 0.42 mmol / g.

When the amount of sulfur introduced due to the sulfo group per 1 g (mass) of the sulfonated fine cellulose fiber is 0.42 mmol / g or less, the hydrogen bond between the fibers is strong and the dispersibility tends to decrease. On the contrary, when the amount of sulfur introduced is higher than 0.42 mmol / g, the dispersibility is easily improved, and when it is 0.5 mmol / g or more, the electronic resilience can be strengthened. It becomes easier to maintain a stable and dispersed state. On the other hand, as the amount of sulfur introduced approaches 9.9 mmol / g, there is a concern that the crystallinity will decrease, and the cost of introducing sulfur tends to increase.
Therefore, it is preferable to adjust the amount of the sulfo group introduced into the sulfonated fine cellulose fiber, that is, the amount of sulfur introduced due to the sulfo group so as to be within the above range.

In particular, the amount of sulfo groups introduced into the sulfonated fine cellulose fibers (the amount of sulfur introduced due to the sulfo groups) is higher than 0.42 mmol / g from the viewpoint of dispersibility of the fine fibers constituting the sulfonated pulp fibers. It is preferably adjusted to 3.0 mmol / g or less, more preferably 0.5 mmol / g to 3.0 mmol / g, still more preferably 0.5 mmol / g to 2.0 mmol / g. Even more preferably, it is 0.5 mmol / g to 1.7 mmol / g, and even more preferably 0.5 mmol / g to 1.5 mmol / g.
Further, from the viewpoint of transparency of the sulfonated fine cellulose fiber, it is preferable to adjust the range so as to be the same as the above range.

(Method of measuring the amount of sulfo group introduced)
The amount of sulfo group introduced into the sulfonated fine cellulose fiber can be evaluated by the amount of sulfur introduced due to the sulfo group. Specifically, a predetermined amount of sulfonated fine cellulose fibers can be burned, and the sulfur content contained in the combusted product can be measured by a method according to IEC 62321 using a combustion ion chromatograph.
Further, when the sulfonated fine cellulose fiber is prepared from the sulfonated pulp fiber described later, it may be obtained from the amount of sulfur introduced in the sulfonated pulp fiber.

If the average fiber length and average fiber width of the sulfonated fine cellulose fibers are adjusted so that the fibers are easily entangled with each other and transparent when dispersed in an aqueous solvent, the length and thickness thereof will be the same. Not particularly limited. For example, it can be prepared to the size shown below.

(Average fiber length of sulfonated fine cellulose fibers)
The average fiber length of the sulfonated fine cellulose fibers can be indirectly expressed by the degree of polymerization.
For example, the sulfonated fine cellulose fiber can be adjusted so that the degree of polymerization is 280 or more. Specifically, the sulfonated fine cellulose fiber is preferably prepared so that the degree of polymerization is 300 to 1,000, and more preferably the degree of polymerization is 300 to 600. When the degree of polymerization of the sulfonated fine cellulose fibers is lower than 280, the entanglement of the fibers tends to be weakened due to the decrease in the fiber length.
Therefore, when the sulfonated fine cellulose fiber is represented by the degree of polymerization, it is preferable to adjust the degree of polymerization so as to be within the above range.

When the axial length of one glucose molecule is about 5 Å (about 0.5 nm) and the degree of polymerization of the sulfonated fine cellulose fiber is 300, the fiber length is theoretically about 150 nm (about 0 nm). .15 μm) of sulfonated fine cellulose fibers can be prepared.

(Method of measuring degree of polymerization)
The method for measuring the degree of polymerization when the average fiber length of the sulfonated fine cellulose fibers is expressed by the degree of polymerization is not particularly limited.
For example, it can be measured by the copper ethylenediamine method. Specifically, the degree of polymerization of the sulfonated fine cellulose fiber can be measured by dissolving the sulfonated fine cellulose fiber in a 0.5 M copper ethylenediamine solution and measuring the viscosity of the solution by the viscosity method.

(Average fiber width of sulfonated fine cellulose fibers)
The average fiber width of the sulfonated fine cellulose fibers is not particularly limited as long as it has a thickness that makes it easy to obtain transparency when dispersed in an aqueous solvent.
For example, the average fiber width of the sulfonated fine cellulose fibers is preferably adjusted to be 1 nm to 1000 nm when observed with an electron microscope, more preferably 2 nm to 500 nm, and even more preferably 2 nm to 100 nm. , More preferably 2 nm to 30 nm, and even more preferably 2 nm to 20 nm.
When the fiber width of the fine cellulose fiber is less than 1 nm, it is in a state of being dissolved in water as a cellulose molecule, so that the physical properties (strength, rigidity, or dimensional stability) of the fine cellulose fiber are difficult to be exhibited. .. On the other hand, if it exceeds 1000 nm, it cannot be said to be a fine cellulose fiber and is merely a fiber contained in ordinary pulp, so that it tends to be difficult to obtain physical characteristics (transparency, strength, rigidity, or dimensional stability) as a fine cellulose fiber. It is in.
Therefore, the average fiber width of the sulfonated fine cellulose fibers is preferably adjusted to be within the above range.

In particular, from the viewpoint of applications where the handleability and transparency of the sulfonated fine cellulose fiber are required, it is more preferable to prepare the sulfonated fine cellulose fiber so as to be within the following range.
When the average fiber width of the sulfonated fine cellulose fibers is larger than 30 nm, the aspect ratio tends to decrease and the entanglement between the fibers tends to decrease. Further, when the average fiber width is larger than 30 nm, it approaches 1/10 of the wavelength of visible light, and when it is combined with a matrix material, visible light is likely to be refracted and scattered at the interface, and visible light is scattered. Therefore, the transparency tends to decrease.
Therefore, the average fiber width of the sulfonated fine cellulose fibers is preferably 2 nm to 30 nm, more preferably 2 nm to 20 nm, and further preferably 2 nm to 10 nm from the viewpoint of handleability and transparency.
From the viewpoint of transparency, it is preferable to prepare the sulfonated fine cellulose fibers so that the average fiber width is 20 nm or less, and more preferably 10 nm or less. If the average fiber width is adjusted to 10 nm or less, the scattering of visible light can be further reduced, so that sulfonated fine cellulose fibers having high transparency can be obtained.

(Measuring method of average fiber width)
The average fiber width of the sulfonated fine cellulose fibers can be measured using a known technique.
For example, the sulfonated fine cellulose fibers are dispersed in a solvent such as pure water, and the mixed solution is adjusted so as to have a predetermined mass%. Then, this mixed solution is spin-coated on a silica substrate coated with PEI (polyethyleneimine), and sulfonated fine cellulose fibers on the silica substrate are observed.
As an observation method, for example, a scanning probe microscope (for example, manufactured by Shimadzu Corporation; SPM-9700) can be used. Twenty sulfonated fine cellulose fibers in the obtained observation image are randomly selected, and the average fiber width of the sulfonated fine cellulose fibers can be obtained by measuring and averaging each fiber width.

(Haze value)
The transparency of the sulfonated fine cellulose fiber can be evaluated by the transparency in the dispersed state. Specifically, the transparency when the dispersion liquid adjusted so that the solid content concentration when the sulfonated fine cellulose fibers are dispersed in the dispersion liquid becomes a predetermined concentration can be evaluated by the haze value. ..

The solid content concentration of the dispersion liquid in which the sulfonated fine cellulose fibers are dispersed is not particularly limited. For example, it can be prepared by dispersing sulfonated fine cellulose fibers in a water-soluble solvent so that the solid content concentration is 0.1% by mass to 20% by mass.
When the haze value of the dispersion is 20% or less, it can be said that the sulfonated fine cellulose fibers have transparency. Conversely, when the haze value of the dispersion prepared so that the solid matter concentration is within the above range is higher than 20%, it can be said that transparency is not properly exhibited. More specifically, when the solid content concentration of the dispersion liquid in which the sulfonated fine cellulose fibers are dispersed is adjusted to 0.2% by mass to 0.5% by mass, the haze value of this dispersion liquid is 20%. If it is the following, it is in a state where the transparency is appropriately exhibited, more preferably 15% or less, and further preferably 10% or less, it is a sulfonated fine cellulose fiber having more transparency. ..

Therefore, from the viewpoint of transparency, the sulfonated fine cellulose fiber is prepared so that the haze value of the dispersion prepared so that the solid content concentration is 0.1% by mass to 20% by mass is 20% or less. Is preferable, and more preferably, the haze value of the dispersion liquid when the solid content concentration is adjusted to 0.2% by mass to 0.5% by mass is adjusted to be within the above range.

The solvent of this dispersion is not particularly limited as long as it is a water-soluble solvent (water-soluble solvent) as in the case of the above-mentioned aqueous solvent. For example, as the water-soluble solvent, not only water alone, but also alcohol, ketone, amine, carboxylic acid, ether, amide and the like may be used alone or in combination of two or more.

(Measurement method of haze value)
The haze value can be measured as follows.
The sulfonated fine cellulose fibers are dispersed in the above-mentioned dispersion liquid so as to have a predetermined solid content concentration. Then, if this dispersion is measured using a spectrophotometer in accordance with JIS K 7105, the haze value, which is the transparency of the sulfonated fine cellulose fibers, can be obtained.

(Total light transmittance)
For the sulfonated fine cellulose fiber, it is preferable to adjust the total light transmittance so that the transparency can be more appropriately evaluated within the haze value of the above-mentioned dispersion liquid. For example, the total light transmittance (%) of the above-mentioned dispersion liquid is preferably 90% or more, and more preferably 95% or more.

(Measurement method of total light transmittance)
The total light transmittance can be measured as follows.
The sulfonated fine cellulose fibers are dispersed in the above-mentioned dispersion liquid so as to have a predetermined solid content concentration. Then, if this dispersion is measured using a spectrophotometer in accordance with JIS K 7105, the total light transmittance of the sulfonated fine cellulose fibers can be determined.

In addition, in this specification, transparency includes the property of both transparency and turbidity of a liquid, or one of them. In the evaluation of transparency, the haze value can more appropriately evaluate the turbidity of the liquid, and the total light transmittance can more appropriately evaluate the transparency.

As described above, by adjusting the average fiber length and the average fiber width of the sulfonated fine cellulose fibers so as to be within the above ranges, excellent transparency can be exhibited for the sulfonated fine cellulose fibers. Moreover, the sulfonated fine cellulose fibers can be easily entangled with each other. Therefore, in a composite material or the like using sulfonated fine cellulose fibers, it is possible to exhibit excellent transparency and high strength.

(viscosity)
When the sulfonated fine cellulose fiber has the above-mentioned characteristics, the sulfonated fine cellulose fiber has a predetermined viscosity.
Specifically, when the sulfonated fine cellulose fiber is prepared so as to have a predetermined solid content concentration (for example, 0.2 to 0.5% by mass), the viscosity of the liquid becomes 10,000 mPa · s or more. can do. That is, the sulfonated fine cellulose fiber has the above-mentioned excellent transparency (low haze value, high total light transmittance), and the dispersed dispersion also has excellent viscosity. As a factor that contributes to the improvement of the viscosity of this dispersion, the sulfo group at the C6 position of the sulfonated fine cellulose fiber can be mentioned.
As described above, the sulfonated fine cellulose fiber is produced based on naturally-derived cellulose, and the dispersed dispersion has excellent transparency and high viscosity (high viscosity). The transparent material can be used as a thickener in various fields such as medicine and food as well as industry.

(Viscosity measurement method)
The viscosity can be measured using a B-type viscometer.
For example, if a liquid prepared so that the solid content concentration of the sulfonated fine cellulose fibers is 0.5% by mass is measured using a B-type viscometer at a rotation speed of 6 rpm, 25 ° C., and 3 minutes, sulfonated The viscosity of the fine cellulose fibers can be measured.

(Position of introduction of sulfo group in sulfonated fine cellulose fiber)
Further, the sulfonated fine cellulose fiber is one in which the hydroxyl groups of some glucose units constituting the cellulose fibers are sulfonated with sulfo groups as described above.
The substitution position of the sulfo group is not particularly limited, but it is preferably prepared in a state in which the sulfo group is preferentially substituted with the hydroxyl group at the C6 position of the glucose unit (see FIG. 21). That is, the sulfonated fine cellulose fiber is prepared so that the hydroxyl group at the C6 position of at least a part of the glucose units constituting the cellulose fiber is replaced with a sulfo group.

The hydroxyl group at the C6 position of this glucose unit is arranged so as to protrude three-dimensionally (see FIG. 21). That is, in the sulfonated fine cellulose fiber, the sulfo group is preferentially introduced into the hydroxyl group at the C6 position arranged so as to protrude from the glucose unit in the exposed portion of the fiber surface.
Therefore, if the sulfonated fine cellulose fibers are dispersed in a water-soluble solvent such as water, the sulfo groups are preferentially arranged on the fiber surface of the sulfonated fine cellulose fibers. Then, due to the charge repulsion between the sulfo groups arranged on the surface, the adjacent sulfonated fine cellulose fibers can be more appropriately dispersed, so that more excellent dispersibility can be exhibited. it can.

Therefore, if the sulfonated fine cellulose fibers are prepared so as to have the above-mentioned excellent transparency (low haze value, high total light transmittance) and dispersed in a water-soluble solvent such as water, the dispersion liquid can be obtained. The dispersed sulfonated fine cellulose fibers can be dispersed in a state where a large number of sulfo groups having charge repulsion are arranged on the surface. Therefore, since it can be uniformly dispersed in a dispersion liquid such as a water-soluble solvent, excellent transparency can be appropriately maintained.

Further, since the sulfonated fine cellulose fiber has a sulfo group at the C6 position, the fiber shape is clearer than that in which a sulfo group is introduced in addition to the C6 position (that is, the sulfonated fine fiber at the C2-C3 position). It's different.
Specifically, the sulfonated fine cellulose fiber is obtained by defibrating the sulfonated pulp as described above. Here, since the sulfonated pulp before mechanical defibration has a sulfo group at the C6 position as described above, it has a higher degree of polymerization and a higher degree of crystallization than the sulfonated pulp at the C2-C3 position. have. That is, the degree of polymerization and the degree of crystallization of the sulfonated fine cellulose fiber and the sulfonated pulp at the C2-C3 position (the pulp before the defibration of the sulfonated fine fiber at the C2-C3 position) are significantly different in the fiber shape. The former (sulfonated fine cellulose fiber) has a higher degree of polymerization and crystallinity than the latter. In other words, the fiber shape of the starting material is significantly different between the sulfonated fine cellulose fiber and the sulfonated fine fiber at the C2-C3 position as described above.

Therefore, even if the values of the degree of polymerization and the degree of crystallinity of the obtained fine fibers are close to each other, the sulfonated fine cellulose fibers obtained by defibrating pulp having different fiber shapes as starting materials and C2- The sulfonated fine fibers at the C3 position also have different fiber shapes. That is, while the sulfonated fine cellulose fiber is a fiber defibrated by a mechanical force, the sulfonated fine fiber at the C2-C3 position is a fiber defibrated by a chemical force. is there.
Since the fiber shapes are different in this way, the sulfonated fine cellulose fiber having a sulfo group at the C6 position has a sulfo group at the C2-C3 position in a state where the sulfonated fine cellulose fiber is dispersed in the solution. Compared to fibers, it can exhibit high viscosity.
Therefore, it is possible to provide sulfonated fine cellulose fibers capable of imparting the above-mentioned high viscosity in addition to imparting the above-mentioned transparency to the dispersion liquid when dispersed in a solution such as water. it can. That is, the sulfonated fine cellulose fiber obtained by refining the sulfonated pulp fiber in which the sulfo group is preferentially introduced at the C6 position has excellent dispersibility when mixed with a liquid, and the obtained dispersion is obtained. The liquid has excellent transparency and high viscosity.
Needless to say, the sulfonated fine cellulose fibers can impart the above-mentioned viscosity to the dispersion liquid in a state of being dispersed in the solution regardless of the presence or absence of transparency.

<Manufacturing method of sulfonated fine cellulose fiber and sulfonated pulp fiber>
The sulfonated pulp fiber, derivative pulp and sulfonated fine cellulose fiber can be produced by the sulfonated pulp fiber manufacturing method and the sulfonated fine cellulose fiber manufacturing method shown below.

The outline of the sulfonated pulp fiber manufacturing method is a method for producing sulfonated pulp fiber by subjecting pulp, which is a fiber raw material to be described later, to a chemical treatment step, and in this chemical treatment step, the supplied pulp is treated in a contact step. After that, it is treated in the reaction process.

In the present specification, the fiber raw material refers to a fibrous raw material such as pulp containing a cellulose molecule, and the pulp refers to an aggregate of a plurality of pulp fibers. Further, the pulp fiber is a collection of a plurality of cellulose fibers, and the cellulose fiber is a collection of a plurality of fine fibers (for example, microfibrils). The fine fibers are a collection of a plurality of cellulose molecules (hereinafter, also simply referred to as cellulose) which are chain polymers in which D-glucose is β (1 → 4) glycosidic bonded. The details of the fiber raw material will be described later.

The outline of the sulfonated fine cellulose fiber production method is a method in which pulp as a fiber raw material is subjected to a chemical treatment step, and then a fine treatment step of refining the pulp after the chemical treatment step is performed in order.
In the sulfonated fine cellulose fiber, at least the hydroxyl groups of the cellulose constituting the fine cellulose fiber are obtained by directly supplying the fiber raw material in a non-sulfonated state to the above-mentioned micronization treatment step to obtain the fine cellulose fiber. It may be prepared by substituting a part with a sulfo group, or the sulfonated pulp fiber obtained by the production method described below, that is, the sulfonated pulp fiber production method, is supplied to the above-mentioned micronization treatment step to be finely prepared. You may. If the latter method is adopted, sulfonated pulp fibers in which some of the hydroxyl groups of the cellulose fibers are already substituted with sulfo groups are supplied to the micronization treatment step, so that it becomes easier to prepare desired sulfonated fine cellulose fibers. Benefits are obtained.
Therefore, in the following description, a case where a sulfonated pulp fiber produced by using the sulfonated pulp fiber manufacturing method is used in the sulfonated fine cellulose fiber manufacturing method will be described as a representative.

As described above, the derivative pulp can be prepared by using an aggregate of a plurality of sulfonated pulp fibers produced by the sulfonated pulp fiber production method, and therefore the production method will be omitted.

The production method shown below is only an example, and is not limited to the following method as long as it can produce sulfonated pulp fibers and sulfonated fine cellulose fibers having the above-mentioned characteristics.

First, the sulfonated pulp fiber manufacturing method will be described, and then the sulfonated fine cellulose fiber manufacturing method will be described.

<Manufacturing method of sulfonated pulp fiber>
As shown in FIG. 1, the sulfonated pulp fiber production method includes a chemical treatment step of chemically treating a fiber raw material containing cellulose by the method shown below.

(Chemical treatment process)
The chemical treatment step in the sulfonated pulp fiber production method includes a contact step of bringing a sulfonate having a sulfo group to a fiber raw material containing cellulose and urea and / or a derivative thereof, and a fiber raw material after this contact step. It includes a reaction step of introducing a sulfo group into at least a part of the hydroxyl group of the cellulose fiber.
That is, the sulfonated pulp fiber production method is characterized in that urea and / or a derivative thereof is used in the method of introducing a sulfo group into the cellulose fiber contained in the fiber raw material. Therefore, an excellent effect that cannot be obtained by the conventional manufacturing method as shown below is obtained.

Generally, as a method of introducing a sulfo group into the cellulose fiber contained in the fiber raw material, a method of performing heat treatment in a state where only the sulfonate agent is in contact with the fiber raw material can be considered.
However, when the reaction is carried out using only the sulfonate agent, 1) the time required for introducing the sulfo group becomes longer, 2) the acid of the sulfonic acid agent tends to shorten the fiber, and 3) ) Due to the influence of the acid of the sulfonic acid agent, the fibers after the reaction are colored, and various chemical treatments are required to process this coloring, which causes problems such as labor and cost for removing the coloring. ..

On the other hand, in the sulfonated pulp fiber manufacturing method, as described above, a method of contacting a fiber raw material with urea and / or a derivative thereof in addition to a sulfonate agent is adopted. Therefore, it is possible to solve the problems 1) to 3) described above when the reaction is carried out only with the sulfonate as in the prior art.

Specifically, the sulfonate and urea and / or its derivative are brought into contact with each other at a predetermined ratio and then reacted.
A) The amount of sulfo group introduced can be promoted. In other words, by using urea as a catalyst, the reaction time can be shortened.
B) On the other hand, urea can suppress the action of shortening fibers by acid. That is, it is possible to prevent the fibers from being shortened by acid (see FIGS. 4 and 21).
C) Coloring of fibers by acid can be suppressed by urea. That is, it is characterized in that it is possible to prepare fibers in which coloring of the fibers is suppressed even though the fibers are treated with an acid (see Table 4), which is an effect that has not been obtained in the past.
D) Moreover, the obtained sulfonated pulp fiber also has the effect that it can be adjusted to have the water retention degree as described above.
E) Further, in the sulfonated pulp fiber production method, since urea and / or a derivative thereof is used as a reaction solution together with a sulfonate agent, water can be used as a solvent for the reaction solution.

Here, usually, when the fiber raw material is reacted with a sulfonate agent for esterification, an organic solvent such as DMF is used as the solvent of the reaction solution.
Water is an excellent solvent in terms of handleability and cost, but is not suitable for an esterification reaction using a sulfonate agent. This is because when the medium fiber raw material and the sulfonater are reacted in an aqueous solvent, the hydroxyl groups of water become rich, so that the sulfonater's reactivity to the hydroxyl groups existing on the surface of the fiber raw material becomes low, and the fiber This is because the reactivity with the hydroxyl group in the raw material is reduced. That is, when the fiber raw material and the sulfonate agent are reacted in an aqueous solvent, there arises a problem that the reaction efficiency of esterification is lowered.
Moreover, in an aqueous solvent, the sulfonate is likely to generate protons. The generated protons cause a cleavage reaction of glycosidic bonds in the fiber raw material (for example, pulp fiber), so that the fiber raw material is also shortened.
Furthermore, there is a concern that the sulfonate agent itself reacts with water and decomposes, further reducing the reactivity.

Therefore, in general, an organic solvent is used in the esterification reaction using a sulfonate agent. In an organic solvent, the proton of the sulfonate agent can be reacted in a state where it is difficult to dissociate. Therefore, if the sulfonate agent and the fiber raw material are reacted in an organic solvent, the esterification reaction of both can proceed preferentially as compared with the case where an aqueous solvent is used.
Moreover, since the sulfonate is less likely to generate protons than the aqueous solvent, the cleavage reaction of the glycosidic bond in the fiber raw material (for example, pulp fiber) can be less likely to occur. Therefore, it is better to react with an organic solvent for the fiber raw material. It is believed that shortening of fibers can be suppressed.

However, in the sulfonated pulp fiber production method, the hydroxyl groups in the fiber raw material can be appropriately esterified with the sulfonate agent by using urea and / or a derivative thereof in addition to the sulfonate agent in the reaction solution of the aqueous solvent. become able to. It is presumed that the following reactions are proceeding in an aqueous solvent.

When a proton is generated in the sulfonate in an aqueous solvent, it is considered that the urea accepts this proton and becomes a salt of a certain sulfonate. Therefore, it is possible to suppress the cleavage reaction of the glycosidic bond by the sulfonate agent in the aqueous solvent.
Moreover, since the fiber of the fiber raw material can be swelled by urea, the salt of urea and the sulfonate can be infiltrated into the fiber of the fiber raw material. Then, when the fiber is heated in the reaction step of the sulfonated pulp fiber production method described later, esterification can proceed even inside the infiltration destination fiber. Specifically, the esterification reaction can proceed not only with the hydroxyl groups in the fiber on the surface of the fiber raw material but also with the hydroxyl groups existing inside the fiber. More specifically, since esterification with a sulfonate can be formed inside the fiber raw material and even on the surface of microfibrils, it is possible to form fibers having a very narrow fiber width after the defibration treatment. become able to. Then, since the protons generated in the sulfonate are suppressed by urea as described above, the shortening of the fiber raw material can be suppressed.
Therefore, after the defibration treatment, fibers having a long fiber length and a very narrow fiber width can be formed.

The fibers having a very fine fiber width after the defibration treatment correspond to sulfonated fine cellulose. Further, the coloring of the fiber can be expressed by the whiteness of the fiber.

In the sulfonated pulp fiber production method, by controlling the water retention degree of the sulfonated pulp fiber, it is possible to obtain further advantages in the production method in addition to the advantages described in the water retention degree in the sulfonated pulp fiber described above. Hereinafter, a specific description will be given.

Here, when fine fibers such as pulp are refined using a defibrator or the like to produce fine fibers such as nanofibers, the efficiency of miniaturization is important both economically and environmentally.
Usually, as a method of improving efficiency performed in such a miniaturization treatment step, the degree of polymerization of the fiber before miniaturization is lowered (that is, the fiber length of the fiber supplied to the defibrator or the like is shortened) to solve the problem. A method of reducing the load on defibration, etc. when supplied to a fiber machine or the like is adopted.
However, although such a conventional method can improve the miniaturization efficiency, there is a problem that the average fiber length of the obtained fine fibers becomes short.

On the other hand, in order to increase the average fiber length of the obtained fine fibers, a defibrator or the like is used in a state where the degree of polymerization of the fibers before miniaturization is maintained high (that is, the fiber length of the fibers supplied to the defibrator or the like is increased). Need to be supplied to.
However, in such a conventional method, although the fiber length of the fine fibers can be increased to some extent, the fibers are in a very hard state (for example, a state in which the fine fibers constituting the fibers are firmly bonded to each other). Therefore, it cannot be easily miniaturized with a defibrator or the like.
Therefore, a large amount of energy (for example, when a high-pressure homogenizer is used, the pressure is increased to 200 MPa or more) and time (for example, a shearing device having a high-speed cutter (M-Technique, Clairemix)) for defibrating. It takes about 30 minutes when the above is used, which causes a problem that not only the work efficiency is deteriorated but also the miniaturization efficiency is extremely deteriorated. Moreover, there is a problem that it is difficult to obtain fine fibers having a uniform fiber length.

On the other hand, in the sulfonated pulp fiber manufacturing method, the above-mentioned conventional problems can be solved by preparing the sulfonated pulp fiber while controlling it so as to have a predetermined water retention degree as described above. Will be.

(Advantages of increasing water retention)
For example, by increasing the water retention of the sulfonated pulp fiber produced by the sulfonated pulp fiber production method (for example, the water retention is made higher than 180%, more preferably 200% or more, still more preferably 250% or more. As described above, the binding force between the fine fibers constituting the sulfonated pulp fiber is weakened, and the surface of the sulfonated pulp fiber and the portion located inward near the surface can be easily fibrillated.
Then, since the fibers constituting the sulfonated pulp fibers can be easily loosened, the energy required for the miniaturization treatment can be reduced. For example, in the case of miniaturization processing using a high-pressure homogenizer, the pressure can be lowered or the number of treatments (number of passes) can be reduced. Therefore, it is possible to reduce the burden on the environment by reducing the amount of energy.
Moreover, since the miniaturization process can be performed smoothly, the time required for the miniaturization process can be shortened, so that the productivity can be improved. In other words, since the productivity can be improved, the manufacturing cost (production cost) can be reduced as compared with the case of manufacturing by the conventional technique.
Further, the micronization treatment makes it possible to supply sulfonated fine cellulose fibers that impart excellent transparency and excellent viscosity to the dispersion liquid.

(Advantages when the water retention level is low)
On the contrary, if the water retention rate of the sulfonated pulp fiber produced by the sulfonated pulp fiber manufacturing method is lowered, the following advantages can be obtained.
If the sulfonated pulp fiber is manufactured so as to have a low water retention degree, the amount of water in the fiber can be reduced, so that the dehydration property can be improved. In this case, since dehydration is facilitated, sulfonated pulp fibers having a high solid content concentration can be produced. Then, it becomes possible to suppress the transportation cost when transporting the produced sulfonated pulp fiber.
Moreover, when the manufacturing step includes a step of washing the sulfonated pulp fiber, dehydration after the washing step becomes easy, so that operability and workability can be improved. Therefore, when the sulfonated pulp fiber is produced for the above purpose, the productivity can be improved. In other words, since the productivity can be improved, the manufacturing cost (production cost) can be reduced as compared with the case of manufacturing by the conventional technique.

Therefore, in the sulfonated pulp fiber manufacturing method, by adjusting the water retention degree of the produced sulfonated pulp fiber, it is possible to produce the sulfonated pulp fiber in which the state of the sulfonated pulp fiber is appropriately adjusted according to the request of the supplier. it can.

In summary, by using the sulfonated pulp fiber manufacturing method, it is possible to produce sulfonated pulp fibers that exhibit the effects of A) to D) as described above, so that the sulfonated pulp has excellent quality stability and excellent handleability. The fiber can be produced with a high recovery rate (for example, a recovery rate of 70% or more).
Moreover, since high-quality sulfonated pulp fibers can be stably produced, sulfonated pulp fibers can be efficiently produced according to a desired purpose of use and application. Further, the manufacturing cost can be suppressed.

Hereinafter, each step of the chemical treatment step will be described in more detail.

(Contact process)
The contact step in the chemical treatment step of the sulfonated pulp fiber production method is a step of contacting the sulfonate with the urea and / or its derivative with the fiber raw material containing cellulose. This contact step is not particularly limited as long as it is a method capable of causing the contact.
For example, the fiber raw material may be immersed in a reaction solution in which a sulfonate agent and urea and / or a derivative thereof coexist to impregnate the reaction solution, or the reaction solution may be applied to the fiber raw material. Then, the sulfonate and urea and / or a derivative thereof may be separately applied or impregnated with the fiber raw material.
Among these methods, if the method of immersing the fiber raw material in the reaction solution and impregnating the fiber raw material with the reaction solution is adopted, the sulfonate and urea and / or its derivative are uniformly brought into contact with the fiber raw material. It is preferable because it can be used.

(Mixing ratio of reaction solution)
When the method of immersing the fiber raw material in the reaction solution and impregnating the fiber raw material with the reaction solution is adopted, the mixing ratio of the sulfonate and urea and / or its derivative contained in the reaction solution is not particularly limited.
For example, the sulfonate and urea and / or its derivatives are in a concentration ratio (g / L) of 4: 1 (1: 0.25), 2: 1 (1: 0.5), 1: 1, 1 : Can be adjusted to 2.5.

When the sulfonate and urea were dissolved in water and the concentrations were adjusted to 200 g / L and 100 g / L, respectively, the concentration ratio (g / L) was 2: sulfonate: urea. The reaction solution of 1 can be prepared. In other words, if urea is prepared so as to be 50 parts by weight with respect to 100 parts by weight of sulfamic acid, a reaction solution having a sulfonate: urea of 2: 1 can be prepared.
Further, if the sulfonate and urea are dissolved in water and the respective concentrations are adjusted to 200 g / L and 500 g / L, the sulfonate: urea is 1: in the concentration ratio (g / L). A reaction solution of 2.5 can be prepared.

(Contact amount of reaction solution)
The amount of the reaction solution to be brought into contact with the fiber raw material is also not particularly limited.
For example, in a state where the reaction solution and the fiber raw material are in contact with each other, the sulfonate contained in the reaction solution is 1 part by weight to 20,000 parts by weight with respect to 100 parts by weight of the dry weight of the fiber raw material. The urea and / or its derivative contained in the above can be prepared so as to be 1 part by weight to 100,000 parts by weight with respect to 100 parts by weight of the dry weight of the fiber raw material.

The degree of water retention can be determined by a general test method as described above (for example, a method based on the Japan TAPPI pulp and paper test method No. 26: 2000).

(Reaction process)
The fiber raw material containing the sulfonate, urea and / or its derivative and water in the contact step is supplied to the reaction step of the next step. In the reaction step in the chemical treatment step of this sulfonated pulp fiber manufacturing method, as described above, the sulfo group of the sulfonate agent brought into contact with the hydroxyl group of the cellulose fiber contained in the fiber raw material is replaced with the cellulose fiber contained in the fiber raw material. This is a step of introducing a sulfo group into the fiber.
This reaction step is not particularly limited as long as it is a method capable of a sulfonation reaction in which the hydroxyl group of the cellulose fiber is substituted with a sulfo group.

For example, if the fiber raw material impregnated with the reaction solution is heated at a predetermined temperature, the sulfo group can be appropriately introduced into the cellulose fiber contained in the fiber raw material.
Specifically, in the reaction step in the chemical treatment step of the sulfonated pulp fiber production method, if heated, the sulfonation reaction can proceed while supplying heat to the supplied fiber raw material. That is, if heating is performed in the reaction step, a sulfonation reaction is carried out in which a sulfo group is introduced into the hydroxyl groups of the cellulose fibers contained in the fiber raw material while drying the fiber raw material in which the reaction solution is impregnated and / or adhered. Can be made.
In this case, the heat treatment in the reaction step reduces the amount of water around the fiber raw material (the amount of water in the reaction solution adhering to the fiber raw material, that is, the water content in the fiber raw material) when the sulfonation reaction is carried out. Therefore, it becomes possible to carry out the sulfonation reaction in a state where the influence of such water content (for example, reaction failure, hydrolysis, etc.) is suppressed.
Therefore, in the reaction step, by carrying out the reaction while heating at a predetermined temperature, it is possible to improve the efficiency of introducing the sulfo group into the hydroxyl group of the cellulose fiber while suppressing damage to the cellulose fiber contained in the supplied fiber raw material. Can be done. Moreover, as will be described later, the sulfo group can be appropriately introduced into a predetermined hydroxyl group of the cellulose fiber in a short time.

The fiber raw material to be supplied to the reaction step is not particularly limited as long as it contains water as described above. For example, the fiber raw material to be supplied to the reaction step may have a high water content after the contact step, or may be dehydrated or the like to lower the water content before being supplied to the reaction step. Alternatively, the water content may be further lowered by a drying treatment or the like. In other words, the fiber raw material to be supplied to the reaction step is not particularly limited as long as it is in a state other than that containing no water, that is, in a non-absolute state having a water content of 1% or more.

In the present specification, such a non-dehydrated fiber raw material having a water content of 1% or more is referred to as a state containing water (that is, a wet state), and is a state in which the reaction solution is impregnated or the like. Not only those that have been dehydrated to some extent, but also those that have been dried to some extent are referred to as wet states in the present specification.
In the present specification, the term "absolutely dry" means a state in which the moisture content is lower than 1%. The drying treatment step of making the product absolutely dry means, for example, a step of reducing the pressure with a desiccator containing a desiccant such as calcium chloride or diphosphorus pentoxide. That is, the step of drying the fiber raw material before supplying it to the reaction step in the specification of the present application is not a drying treatment step of making it absolutely dry.

The state in which the fiber raw material is impregnated with the reaction solution when supplied to the reaction step is, for example, a state in which the reaction solution is brought into contact with the fiber material so that water drips, that is, a state in which the water content is close to 100%. It may be.
Further, a state in which the fiber raw material supplied to the reaction step has water removed from the fiber raw material after the contact step to some extent means that the fiber is in an absolutely dry state when supplied to the reaction step (fibers when supplied to the reaction step). It refers to a state in which the water content of the raw material is not lower than 1%), and is not particularly limited as long as the water content is 1% or more. In such a method of removing water from the fiber raw material after the contact step to some extent, the fiber raw material after the contact step may be subjected to a treatment such as dehydration as described above, or a drying treatment may be performed after the treatment such as dehydration. Alternatively, the fiber raw material after the contact step may be directly dried. In this case, since the water is removed to some extent, there is an advantage that the handleability and operability are improved. As the dehydration treatment, for example, a general treatment method such as suction dehydration or centrifugal dehydration can be adopted, and the water content of the fiber raw material when supplied to the reaction step is adjusted to be about 20% to 80%. can do. Further, as the drying treatment, for example, a drying treatment using a general device such as a dryer can be adopted, so that the water content of the fiber raw material after the drying treatment is 1% or more and less than 20%. Can be adjusted.

The water content in the present specification can be calculated by the following formula.

Moisture content (%) = 100- (solid content weight (g) of fiber raw material / weight of fiber raw material (g) at the time of water content measurement after contact step) × 100

The solid content weight (g) of the fiber raw material is the dry weight of the fiber raw material itself to be measured. For example, a fiber raw material containing about 50% of water content is previously dried at 105 ° C. for 2 hours using a dryer with respect to 2 g of the dry weight of the fiber raw material supplied to the reaction step. The given value can be used.
The weight (g) of the fiber raw material at the time of measuring the water content after the contact step is the weight of the fiber raw material at the time of measuring after the contact step. For example, the weight of the fiber raw material when supplied to the above-mentioned reaction step, the weight of the fiber raw material after the dehydration treatment after the contact step, the weight of the fiber raw material after the drying treatment, and the like can be mentioned.

(Reaction temperature in the reaction process)
The reaction temperature in the reaction step is not particularly limited as long as it is a temperature at which a sulfo group can be introduced into the cellulose fibers constituting the fiber raw material while suppressing the thermal decomposition and hydrolysis reactions of the fibers.
Specifically, the fiber raw material after the contact step may be directly or indirectly heated while satisfying the above requirements. Examples of such a method include a hot press method using a known dryer, a vacuum dryer, a microwave heating device, an autoclave, an infrared heating device, and a heat press machine (for example, AH-2003C manufactured by AS ONE Corporation). Etc. can be adopted. In particular, since gas may be generated in the reaction step, it is preferable to use a circulation blower type dryer.

The shape of the fiber raw material after the contact step is not particularly limited, but it is preferable to heat the fiber raw material in the form of a sheet or in a loosened state to some extent using the above equipment or the like because the reaction can be promoted uniformly. ..

The reaction temperature in the reaction step is not particularly limited as long as the above requirements are satisfied.
For example, the ambient temperature is preferably 250 ° C. or lower, more preferably 200 ° C. or lower, and even more preferably 180 ° C. or lower.
When the atmospheric temperature at the time of heating becomes higher than 250 ° C., thermal decomposition occurs as described above, and the progress of discoloration of the fibers becomes faster. On the other hand, when the reaction temperature is lower than 100 ° C., the reaction time tends to be long.
Therefore, from the viewpoint of workability, the reaction temperature (specifically, the ambient temperature) during heating is 100 ° C. or higher and 250 ° C. or lower, more preferably 100 ° C. or higher and 200 ° C. or lower, and further preferably 100 ° C. or higher and 180 ° C. or lower. Adjust so that.

(Reaction time in reaction process)
The heating time (that is, reaction time) when the above heating method is adopted as the reaction step is not particularly limited as long as the sulfo group can be appropriately introduced into the cellulose fiber as described above.

For example, the reaction time in the reaction step is adjusted to be 1 minute or more when the reaction temperature is adjusted to be within the above range. More specifically, it is preferably 5 minutes or more, more preferably 10 minutes or more, and further preferably 20 minutes or more.
When the reaction time is shorter than 1 minute, it is presumed that the substitution reaction of the sulfo group with respect to the hydroxyl group of the cellulose fiber has hardly proceeded. On the other hand, even if the heating time is too long, the amount of sulfo groups introduced tends not to be improved.
That is, the reaction time in the reaction step may be such that a part of the hydroxyl groups of the cellulose fibers in the fiber raw material can be replaced with a sulfo group by bringing the reaction solution into contact with the fiber raw material. By reacting the sulfonated pulp fiber prepared through this reaction step with the above reaction solution, the fiber length retention rate (%) before and after the reaction can be maintained high (see FIGS. 4 and 6). ).
Therefore, the reaction time when the above heating method is adopted as the reaction step is not particularly limited, but is preferably 5 minutes or more and 300 minutes or less, and more preferably 5 minutes or more and 120 minutes or less from the viewpoint of reaction time and operability. It is better to do it.

In particular, in order to ensure that the dispersion liquid in which the sulfonated fine cellulose fibers obtained after the micronization treatment described later exhibits excellent viscosity, the sulfonated pulp fibers after the reaction are predetermined in the reaction step. It is preferable to prepare it in a state. Specifically, in the reaction step, the sulfonated pulp fiber obtained after the heating reaction is prepared so that the rate of change in the degree of polymerization is smaller than that of the pulp (fiber raw material) subjected to the heating reaction. That is, the sulfonated pulp fiber is prepared so as to maintain a high degree of polymerization and crystallinity with respect to the pulp (fiber raw material) to be subjected to the heating reaction. In other words, it is prepared so that the maintenance rate of the degree of polymerization and the degree of crystallinity after the reaction is high.
For example, the sulfonated pulp fiber has a degree of polymerization ratio (polymerization degree ratio before and after the reaction (polymerization degree after the reaction / polymerization degree before the reaction)) of 50% or more with respect to the pulp (fiber raw material) to be subjected to the heating reaction. Is. The degree of polymerization ratio before and after this reaction (degree of polymerization after reaction / degree of polymerization before reaction) is preferably 55% or more, more preferably 60% or more, still more preferably 80% or more. That is, the rate of change in the fiber state of the sulfonated pulp fiber is small in the degree of polymerization before and after the reaction. Conversely, the maintenance rate of the degree of polymerization after the reaction is high. Therefore, excellent viscosity can be exhibited in the dispersion liquid in which the sulfonated fine cellulose fibers after defibration obtained in the micronization treatment step described later are dispersed.
Regarding the crystallinity, for example, the sulfonated pulp fiber has a crystallinity (that is, a crystallinity ratio before and after the reaction (crystallinity after the reaction / reaction) with respect to the pulp (fiber raw material) to be subjected to the heating reaction. It is 80% or more in the previous crystallinity)). The crystallinity ratio (crystallinity after the reaction / crystallinity before the reaction) before and after this reaction is preferably 85% or more, more preferably 90%. That is, the sulfonated pulp fiber has a small rate of change in crystallinity before and after the reaction. Conversely, the maintenance rate of the crystallinity after the reaction is high. Therefore, excellent viscosity can be exhibited in the dispersion liquid in which the sulfonated fine cellulose fibers after defibration obtained in the micronization treatment step described later are dispersed.
More specifically, the mixing ratio of the sulfonate contained in the reaction solution and urea and / or its derivative is adjusted in the contact step so that the degree of polymerization and crystallinity are maintained in a high state in the reaction step. .. For example, the concentration ratio is preferably adjusted to be within the range of 8: 1 to 1: 5, and more preferably 4: 1 to 1: 2.5. Further, the sulfonate agent is preferably sulfamic acid from the viewpoint of adjusting the degree of polymerization ratio and the degree of crystallinity. (See Tables 14 and 15)

(Sulfonizing agent)
The sulfonate agent in the reaction step is not particularly limited as long as it is a compound having a sulfo group.
For example, sulfamic acid, sulfamate, sulfyl compounds having a sulfonyl group having two oxygen covalently bonded to sulfur, and the like can be mentioned. As the sulfonate agent, these compounds may be used alone, or two or more kinds may be mixed and used.
The sulfonate agent is not particularly limited as long as it is a compound as described above, but it has a lower acidity than sulfuric acid or the like, a high efficiency of introducing a sulfo group, a low cost, and a high safety, so from the viewpoint of handleability , Sulfamic acid is preferably used.

(Urea and its derivatives)
Of the urea and its derivatives in the reaction step, the urea derivative is not particularly limited as long as it is a compound containing urea.
For example, carboxylic acid amide, complex compound of isocyanate and amine, thiamide and the like can be mentioned. Urea and its derivative may be used alone or in combination of both. Further, as the urea derivative, the above compound may be used alone, or two or more kinds may be mixed and used.
Urea and its derivatives are not particularly limited as long as they are the above-mentioned compounds, but it is preferable to use urea from the viewpoint of handleability because it is low in cost, has little influence on the environmental load, and is highly safe.

(Fiber raw material)
The fiber raw material used in the method for producing a sulfonated pulp fiber is not particularly limited as long as it contains cellulose as described above.
For example, what is generally called pulp may be used, or one containing cellulose isolated from sea squirts, seaweed, etc. can be used as a fiber raw material, but if it is composed of cellulose molecules, it can be used. , Anything can be used.
Examples of the above-mentioned pulp include wood-based pulp (hereinafter simply referred to as wood pulp), melted pulp, cotton-based pulp such as cotton linter, straw, bagus, 楮, sansho, hemp, kenaf, and fruits. Non-wood pulp, used newspaper pulp, used paper pulp produced from used magazine paper, used cardboard, etc., but are not limited to these. From the viewpoint of easy availability, wood pulp is easy to use as a fiber raw material.

There are various types of this wood pulp, but the use is not particularly limited. For example, papermaking pulp such as softwood kraft pulp (NBKP), hardwood kraft pulp (LBKP), and thermomechanical pulp (TMP) can be mentioned.
When the above-mentioned pulp is used as the fiber raw material, one of the above-mentioned types of pulp may be used alone, or two or more of them may be mixed and used.

(Drying process)
As described above, the state of the fiber raw material when it is supplied to the reaction step may be a state in which water is contained when it is supplied to the reaction step, and if such a state is maintained, the contact step and the reaction step A drying step may be included between the two.
This drying step is a step that functions as a pretreatment step of the reaction step, and is a step of reducing the water content of the fiber raw material after the contact step.

Here, it is desirable that the fiber raw material after the drying step is adjusted so that the water content is 1% or more. When the fiber raw material in a state where the water content of the fiber raw material after the drying step is lower than 1%, that is, in a state of being dried until it becomes an absolutely dry state is supplied to the reaction step, the hydrogen bond between the fibers in the fiber raw material is formed due to the absolute dry state. It acts strongly and may make it difficult for the sulfonated reaction in the reaction step to proceed properly. Therefore, in the drying step, it is desirable to adjust the water content of the fiber raw material after the drying step to be 1% or more.

Further, if the drying step is provided, the following advantages can be obtained.
If the water content of the fiber raw material when it is supplied to the reaction step is high, there is a possibility that a part of sulfamic acid, urea, etc. may be hydrolyzed by the heating reaction in the reaction step, and the reaction efficiency may decrease. In some cases, an undesired reaction may occur as a fiber raw material for micronization. Therefore, from the viewpoint of suppressing the possibility of damage during the heating reaction, a drying step of lowering the water content of the fiber raw material may be provided before the reaction step.
By providing the drying step, in the reaction step of the next step, the possibility of the above-mentioned obstacles can be suppressed, the reaction time of the esterification reaction can be shortened, and the operability can be improved. That is, by providing the drying step, the water in the reaction liquid adhering to the fiber raw material after the contact step can be appropriately removed when it is supplied to the reaction step, so that the fiber when it is supplied to the reaction step can be obtained. The concentration of sulfamic acid in the raw material can be increased. Therefore, in the reaction step, there is an advantage that the esterification reaction between the hydroxyl group in the fiber raw material and sulfamic acid can be more easily promoted.

In the drying step, the method is not particularly limited as long as the water content of the fiber raw material after the drying step is adjusted to be 1% or more as described above. For example, a dryer may be used to adjust the water content of the fiber raw material after the drying step so that it is in an equilibrium state with the water content in the atmosphere, or the water content is 15% or less, 10% or less, and further. May be adjusted to be up to about 5%.

Here, the equilibrium state in the present specification means a state in which the water content in the atmosphere and the water content in the raw material in the treatment facility apparently do not enter and exit. Specifically, it means a state in which the amount of change in weight measured twice in succession after drying for a certain period of time is within 1% of the weight at the start of drying (however, the weight of the second time). The measurement should be at least half of the drying time required for the first time).

The drying temperature in the drying step is not particularly limited, but it is desirable to dry at a temperature lower than the heating temperature of the heating reaction in the reaction step. If the ambient temperature during heating is higher than 100 ° C., decomposition of the sulfonate and the like may occur. On the other hand, if the ambient temperature during heating is lower than 20 ° C., it takes time to dry. Therefore, the drying temperature in the drying step is, for example, preferably an atmospheric temperature of 100 ° C. or lower, more preferably 20 ° C. or higher and 100 ° C. or lower, and further preferably 50 ° C. or higher and 100 ° C. or lower. That is, the atmospheric temperature during drying in the drying step is preferably 100 ° C. or lower, and is preferably adjusted to 20 ° C. or higher from the viewpoint of operability.

(Washing process)
After the reaction step in the chemical treatment step of the sulfonated pulp fiber production method, a washing step of washing the fiber raw material after introducing the sulfo group may be included.
The surface of the fiber raw material after the introduction of the sulfo group is acidic due to the influence of the sulfonate agent. In addition, an unreacted reaction solution is also present. Therefore, the handleability can be improved by providing a washing step of surely terminating the reaction and removing excess reaction solution to make it in a neutral state.

This washing step is not particularly limited as long as the fiber raw material after introducing the sulfo group can be made substantially neutral.
For example, a method of washing with pure water or the like until the fiber raw material after introducing the sulfo group becomes neutral can be adopted.
Further, neutralization cleaning using alkali or the like may be performed. When such neutralization cleaning is performed, examples of the alkaline compound contained in the alkaline solution include an inorganic alkaline compound and an organic alkaline compound. Examples of the inorganic alkali compound include alkali metal hydroxides, carbonates and phosphates. Examples of the organic alkali compound include ammonia, an aliphatic amine, an aromatic amine, an aliphatic ammonium, an aromatic ammonium, a heterocyclic compound, and a hydroxide of a heterocyclic compound.

<Manufacturing method of sulfonated fine cellulose fiber>
As shown in FIG. 1, the sulfonated fine cellulose fiber is made by supplying the sulfonated pulp fiber prepared by using the sulfonated pulp fiber manufacturing method as described above to the micronization treatment step in the sulfonated fine cellulose fiber manufacturing method. Obtained by doing.

Then, in the sulfonated fine cellulose fiber manufacturing method, if the sulfonated pulp fiber supplied to the micronization treatment step is prepared so as to be in a predetermined fiber state as described above, the dispersion liquid is subjected to the micronization treatment. It is possible to prepare sulfonated fine cellulose fibers that can impart excellent viscosity. The thickening effect of such a dispersion is a phenomenon caused by having a sulfo group at the C6 position. Therefore, in order to impart excellent viscosity to the dispersion liquid when dispersed, it is important to prepare sulfonated fine cellulose fibers in which a sulfo group is preferentially introduced at the C6 position.

(Miniaturization process)
The micronization treatment step in the sulfonated fine cellulose fiber production method is a step of micronizing the sulfonated pulp fiber into fine fibers having a predetermined size (for example, nano level).
The processing apparatus used in this miniaturization processing step is not particularly limited as long as it has the above functions.
For example, a low pressure homogenizer, a high pressure homogenizer, a grinder (stone mill type crusher), a ball mill, a cutter mill, a jet mill, a short shaft extruder, a twin shaft extruder, an ultrasonic stirrer, a household mixer, etc. can be used. , The processing device is not limited to these devices.
Of these, it is desirable to use a high-pressure homogenizer in that the force can be applied evenly to the material and the homogenization is excellent, but the device is not limited to this.

When a high-pressure homogenizer is used in the miniaturization treatment step, the sulfonated pulp fibers obtained by the above-mentioned production method are supplied in a state of being dispersed in a water-soluble solvent such as water. In the following, a solution in which sulfonated pulp fibers are dispersed is referred to as a slurry.

The solid content concentration of the sulfonated pulp fiber of this slurry is not particularly limited. For example, a solution adjusted so that the solid content concentration of the sulfonated pulp fiber of this slurry is 0.1% by mass to 20% by mass may be supplied to a processing apparatus such as a high-pressure homogenizer.
For example, when a slurry adjusted so that the solid content concentration of the sulfonated pulp fiber is 0.5% by mass is supplied to a processing device such as a high-pressure homogenizer, the sulfonated fine cellulose fiber having the same solid content concentration becomes a water-soluble solvent. A dispersion liquid in a dispersed state can be obtained. That is, in this case, it is possible to obtain a dispersion liquid adjusted so that the solid content concentration of the sulfonated fine cellulose fibers is 0.5% by mass.

(Relationship between miniaturization treatment and water retention)
Further, the water retention degree of the sulfonated pulp fiber supplied in the miniaturization treatment step is not particularly limited as long as it is adjusted so as to be easily miniaturized by the above apparatus or the like.

For example, from the viewpoint of miniaturization processing efficiency and reduction of energy consumption, it is desirable to use sulfonated pulp fibers prepared to have a high degree of water retention. From these viewpoints, the water retention rate of the sulfonated pulp fiber is preferably adjusted to 150% or more. In particular, it is preferable to use one prepared so as to be higher than 200%, more preferably 220% or more, still more preferably 250%, even more preferably 300% or more, still more preferably. It is preferable to use the one prepared so as to be 500%. On the other hand, when the water retention rate is higher than 10,000%, the recovery rate of the sulfonated pulp fiber after the sulfonate treatment tends to decrease.

Therefore, from the viewpoint of miniaturization efficiency and recovery rate, the water retention of the sulfonated pulp fiber when supplied to the miniaturization treatment step is preferably 150% to 10,000%, more preferably 200% to 10%. It is 000%, more preferably 220% to 10,000%, even more preferably 250% to 5,000%, and even more preferably 250% to 2,000%.

When the sulfonated pulp fiber used in the miniaturization treatment step has a high degree of water retention, the following advantages can also be obtained.

The higher the water retention level of the sulfonated pulp fiber used in the miniaturization treatment step, the more the fiber swells, so that the fiber is easily loosened.
Therefore, as described above, it is possible not only to improve the miniaturization efficiency of the defibrator or the like used in the pulverization processing step, but also to suppress the occurrence of problems such as fiber clogging in the defibrator or the like used. Therefore, smooth miniaturization (defibration) can be performed, so that a higher concentration pulp fiber can be processed by a defibrator or the like.

Moreover, since smooth miniaturization (defibration) can be performed, the time required for the miniaturization processing step can be further shortened. For example, when a defibrator is used, miniaturization can be performed with a small number of passes.

Here, conventionally, when a high-pressure homogenizer is used as a defibrator for defibration treatment, there is a problem that the higher the defibration pressure of the high-pressure homogenizer, the larger the processing capacity drops. For example, when a general-purpose machine that performs defibration processing at a defibration pressure of 100 MPa or more is used in order to produce fibers of a desired size, the processing amount per hour is extremely high at several hundred liters. The manufacturing efficiency is poor. On the other hand, if this defibration pressure is applied at several tens of MPa, the amount of processing per hour can be several thousand L, which is an order of magnitude higher. However, since the defibration pressure is set low, there is a problem that the fibers cannot be defibrated to a desired size. That is, conventionally, in the defibration treatment of pulp, the defibration treatment with a lower defibration pressure and a smaller number of treatments has been required.
In the sulfonated pulp fiber of the present embodiment, the defibration property can be improved by adjusting the water retention degree, and in the method for producing the sulfonated pulp fiber of the present embodiment, the water retention degree is adjusted to be excellent. Since the sulfonated pulp fiber having defibration property can be produced, the above-mentioned problems in the defibration treatment can be appropriately solved.

In particular, in order for the dispersion liquid in which the sulfonated fine cellulose fibers are dispersed to exhibit excellent viscosity, it is important that the sulfo group is preferentially introduced into the C6 position of the sulfonated fine cellulose fibers. It is as follows. Then, in order to appropriately prepare the sulfonated fine cellulose fiber exhibiting such a function, it is important to grasp the fiber state before and after defibration.
Specifically, in the sulfonated fine cellulose fiber manufacturing method, the sulfonated fine cellulose fiber obtained after the defibration treatment step has a larger rate of change in the degree of polymerization than the sulfonated pulp fiber subjected to the defibration treatment. Have been prepared. That is, the sulfonated fine cellulose fiber is prepared so that the degree of polymerization is lower than that of the sulfonated pulp fiber to be subjected to the defibration treatment. In other words, it is prepared so that the maintenance rate of the degree of polymerization after the defibration treatment (miniaturization treatment) is low.
For example, the sulfonated fine cellulose fiber has a degree of polymerization ratio (degree of polymerization after the fine treatment / degree of polymerization before the fine treatment) of 85% or less with respect to the sulfonated pulp fiber to be subjected to the defibration treatment. Preferably, the degree of polymerization ratio (degree of polymerization after the pulverization treatment / degree of polymerization before the pulverization treatment) before and after the defibration treatment is 80% or less, and more preferably 70% or less.
As described above, the sulfonated fine cellulose fiber has a large rate of change in the degree of polymerization before and after defibration (conversely, a small retention rate after polymerization before and after defibration), so that the sulfonated fine cellulose fiber is finely sulfonated. There is a tendency that the viscosity of the dispersion liquid when the cellulose fibers are dispersed can be increased.

Further, in the sulfonated fine cellulose fiber manufacturing method, the sulfonated fine cellulose fiber obtained after the defibration treatment step is prepared so that the rate of change in the degree of crystallization is larger than that of the sulfonated pulp fiber subjected to the defibration treatment. ing. That is, the sulfonated fine cellulose fiber is prepared so that the crystallinity is lower than that of the sulfonated pulp fiber to be subjected to the defibration treatment. In other words, it is prepared so that the maintenance rate of the crystallinity after the defibration treatment (miniaturization treatment) is low.
For example, the sulfonated fine cellulose fiber has a crystallinity ratio (crystallinity after the finening treatment / crystallinity before the finening treatment) of 75% or less with respect to the sulfonated pulp fiber to be subjected to the defibration treatment. Is. The crystallinity ratio (crystallinity after the pulverization treatment / crystallinity before the pulverization treatment) before and after the defibration treatment is preferably 70% or less, and more preferably 60% or less.
As described above, the sulfonated fine cellulose fiber has a large rate of change in crystallinity before and after defibration (conversely, a decrease in the maintenance rate of crystallinity before and after defibration). There is a tendency that the viscosity of the dispersion liquid when the fine cellulose fibers are dispersed can be increased.

Therefore, by using this production method, the amount of sulfur introduced is adjusted to be within a predetermined range, the introduction position of sulfonation is adjusted to be preferentially performed at the C6 position, and the degree of polymerization and / or crystallinity is adjusted. A sulfonated fine cellulose fiber adjusted so that the degree is within a predetermined range is obtained. Then, when the sulfonated fine cellulose fiber is dispersed in a solution such as water, it is possible to impart a viscosity of a predetermined value or more to the dispersion liquid.

The fiber shape of the sulfonated fine cellulose fiber described above is a phenomenon caused by having a sulfo group at the C6 position, and the reason for this will be described in detail in Examples described later.

The sulfonated pulp fiber of the present invention and the derivative pulp of the present invention can be produced by using the method for producing a sulfonated pulp fiber of the present invention, and the present invention can be produced by using the method for producing a sulfonated fine cellulose fiber of the present invention. It was confirmed that the sulfonated fine cellulose fiber of the present invention could be produced. Further, it was confirmed that the prepared sulfonated pulp fiber of the present invention and the sulfonated fine cellulose fiber of the present invention have predetermined characteristics.

<Experiment 1>
In Experiment 1, softwood kraft pulp (NBKP) (average fiber length 2.6 mm) was used as the fiber raw material. In the following, NBKP used in the experiment will be simply described as pulp.
The pulp was washed with a large amount of pure water, drained with a 200-mesh sieve, the solid content concentration was measured, and the pulp was subjected to an experiment without drying.

(Chemical treatment process)
Pulp was added to the reaction solution prepared as follows and stirred to form a slurry.
The step of adding this pulp to the reaction solution to form a slurry corresponds to the contact step in the chemical treatment step of the method for producing sulfonated pulp fiber of the present embodiment.

(Preparation of reaction solution)
The sulfonate and urea and / or its derivatives were prepared to have the following concentrations.
In Experiment 1, sulfamic acid (purity 98.5%, manufactured by Fuso Chemical Industries) was used as the sulfonate, and urea solution (purity 99%, manufactured by Wako Pure Chemical Industries, Ltd., model number; special grade reagent) was used as urea or a derivative thereof. )It was used.
The mixing ratio of the two is 4: 1 (1: 0.25), 2: 1 (1: 0.5), 1: 1, 1: 2.5 in the concentration ratio (g / L). The mixture was mixed to prepare an aqueous solution. Specifically, sulfamic acid and urea were mixed as follows.
Sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/50, 200/100, 200/200, 200/500, 50/25, 100/50, 200/100

An example of preparation of the reaction solution is shown below.
100 ml of water was added to the container. Then, 20 g of sulfamic acid and 10 g of urea were added to this container to prepare a reaction solution having a sulfamic acid / urea ratio ((g / L) / (g / L)) of 200/100 (1: 0.5). .. That is, urea was added so as to be 50 parts by weight with respect to 100 parts by weight of sulfamic acid.

(Contact process)
2 g (dry weight) of pulp was added to the prepared reaction solution.
For example, in the case of a reaction solution having a sulfamic acid / urea ratio ((g / L) / (g / L)) of 200/100 (1: 0.5), sulfamic acid is added to 100 parts by weight of pulp. It was prepared to be 1000 parts by weight. Urea was adjusted to be 500 parts by weight.

As Comparative Example 1 (“drying step conditional”) and Comparative Example 2 (“drying step unconditional”), a comparative sample (sulfamic acid / urea ratio ((g)) in which urea was not added to the reaction solution at a sulfamic acid concentration of 200 g / L. / L) / (g / L)) = 200/0) was prepared. Comparative Example 1 and Comparative Example 2 were subjected to the same operations as those of the other experimental examples except that urea was not added.
As the blank pulp, NBKP (BL) which was not in contact with the reaction solution was used.

The slurry prepared by adding pulp to the reaction solution was stirred for 10 minutes using a stirrer. After stirring, the slurry was suction filtered using a filter paper (No. 2). Suction filtration was performed until the solution stopped dripping. After suction filtration, the pulp was peeled off from the filter paper, and the filtered pulp was placed in a dryer (manufactured by Isuzu Seisakusho, model number; VTR-115) in which the temperature of the constant temperature bath was set to 50 ° C. and dried until the water content became equilibrium. .. That is, the dried product before the heating reaction was supplied to the next heating reaction step. In the following, the conditions under which this drying is performed are simply referred to as "conditions for the drying process".

The step of bringing the pulp into contact with the reaction solution corresponds to the contact step in the chemical treatment step of the method for producing sulfonated pulp fiber of the present embodiment. The step of suction-filtering the slurry corresponds to the dehydration treatment step in the chemical treatment step of the method for producing sulfonated pulp fibers of the present embodiment. Then, the step of drying the pulp after filtration corresponds to the drying step in the chemical treatment step of the method for producing sulfonated pulp fiber of the present embodiment.

It should be noted that both the "drying step conditional" pulp that was dried under the above conditions before the heating reaction and the "drying step unconditional" pulp that was not dried under the above conditions before the heating reaction were carried out in this manner. Corresponds to the form of non-dry pulp. In addition, the water content of the pulp prepared under any of the conditions of "conditional drying step" and "unconditional drying step" was 1% or more.

The water content was calculated using the following formula. Further, in the evaluation method of the equilibrium state, after drying for 1 hour in the above-mentioned dryer in which the temperature of the constant temperature bath is set to 50 ° C., the amount of change in the weight twice measured continuously is the weight at the start of drying. The state of being within 1% was regarded as the equilibrium state (however, the second weight measurement was set to more than half of the drying time required for the first time).

Moisture content (%) = 100- (Pulp solid content weight (g) / Pulp weight (g) when measuring water content after contact with reaction solution) x 100

The solid content weight (g) of the pulp refers to the dry weight of the pulp itself to be measured, and in this experiment, 2 g of the dry pulp used in the experiment corresponds to it. The weight of the dried pulp was measured by using the above-mentioned dryer to dry the pulp at a temperature of 105 ° C. for 2 hours.
In this experiment, the pulp weight after suction dehydration and the pulp weight after drying correspond to the pulp weight (g) at the time of measuring the water content after contacting with the reaction solution.
In the experiment, the water content of the pulp after suction filtration was 50% to 80%, all of which were 80% or less. The water content of the pulp after drying under the “conditional drying process” was about several% to 10% (drying temperature 50 ° C.).

(Reaction process)
Then, this dried pulp was subjected to the heating reaction step of the next step to carry out the heating reaction.
A dryer (manufactured by Isuzu Seisakusho, model number; VTR-115) was used for the heating reaction.
The reaction conditions of the heating reaction were as follows.
Constant temperature bath temperature: 100 ° C, 120 ° C, 140 ° C, heating time: 5 minutes, 25 minutes, 60 minutes, 120 minutes

This heating reaction corresponds to the reaction step in the chemical treatment step of the method for producing sulfonated pulp fiber of the present embodiment. Further, the temperature of the reaction condition in the heating reaction corresponds to the reaction temperature of the reaction step in the chemical treatment step of the method for producing the sulfonated pulp fiber of the present embodiment, and the heating time of the reaction condition in the heating reaction is the heating time of the present embodiment. It corresponds to the reaction time of the reaction step in the chemical treatment step of the method for producing sulfonated pulp fiber.

After the heating reaction, the reacted pulp was washed with pure water until it became neutral to prepare a sulfamic acid / urea-treated pulp (Examples 1 to 16).

The step of washing the reacted pulp with pure water until it becomes neutral corresponds to the washing step in the chemical treatment step of the method for producing sulfonated pulp fiber of the present embodiment.
Further, the prepared sulfamic acid / urea-treated pulp corresponds to the derivative pulp of the present embodiment, and the reactive pulp fiber constituting the sulfamic acid / urea-treated pulp corresponds to the sulfonated pulp fiber of the present embodiment. That is, the sulfamic acid / urea-treated pulp corresponding to the derivative pulp of the present embodiment is an aggregate of only the sulfamic acid / urea-treated pulp fibers which are the reactive pulp fibers corresponding to the sulfonated pulp fibers of the present embodiment. ..

When the drying step was omitted, the pulp was peeled off from the filter paper after suction filtration and subjected to the heating reaction as it was. That is, it was directly supplied to the heating reaction in the next step without drying as described above before the heating reaction. The reaction conditions for the heating reaction in the next step were the same as described above. In the following, the condition in which the drying is not performed is simply referred to as “drying step unconditional” (Examples 17 to 22).

(Miniaturization process)
Then, the prepared sulfamic acid / urea-treated pulp was nano-sized (miniaturized) using a high-pressure homogenizer (manufactured by GEA Nirosoabi Co., Ltd., model number; Panda Plus 200) to prepare nanocellulose.
The treatment conditions for the high-pressure homogenizer were as follows.
The solid content concentration of the sulfamic acid / urea-treated pulp in the slurry supplied to the high-pressure homogenizer was adjusted to be 0.5% by mass. The defibration pressure of the high-pressure homogenizer was 120 to 140 MPa.
Each sulfamic acid / urea-treated pulp was treated with a high-pressure homogenizer three times (3 passes) to prepare nanocellulose fibers.

The defibration operation using this high-pressure homogenizer corresponds to the miniaturization treatment step in the method for producing sulfonated fine cellulose fibers of the present embodiment. Then, the prepared nanocellulose fiber corresponds to the sulfonated fine cellulose fiber of the present embodiment.

(Pulp yield (%))
The yield of pulp before and after the chemical treatment was calculated from the following formula.
The pulp after the chemical treatment was recovered using a 300 mesh wire.

Yield (%) = (solid content weight (g) of pulp recovered after the chemical treatment step / solid content weight (g) of pulp charged before the chemical treatment step) × 100

In this experiment, 2 g of the dried pulp used in the experiment corresponds to "the solid content weight (g) of the pulp prepared before the chemical treatment step".

(Elemental analysis (sulfur))
The sulfur content in the pulp after the chemical treatment was determined by combustion ion chromatography. The measuring method was measured according to the measuring conditions of IEC 62321.
Combustion device: Mitsubishi Chemical Analytech Co., Ltd., model number: AQF-2100 H
Ion chromatograph: Thermo Fisher Scientific, model number; ICS-1600

(Measurement of water retention)
The water retention of the fiber after the chemical treatment was measured by TAPPI No. as shown below. It was carried out in accordance with 26.
The degree of water retention means that the pulp slurry to be measured is dehydrated in a container called a centrifuge cup, placed in a centrifugal sedimentation tube together with the container, centrifuged at a centrifugal force of 3000 G for 15 minutes, and then remains in the pulp. It is a value expressed as a ratio to the weight of the sample after drying.
In this experiment, the centrifugal cup was a cup of PVC pipe with 300 mesh wire (outer diameter 3.4 cm, inner diameter 2.6 cm, length 7.5 cm, mesh attached inside 1.8 cm from the bottom). Was used. A KUBOTA KR / 702 type centrifuge manufactured by Kubota Seisakusho Co., Ltd. was used for the centrifugation.

First, the washed pulp (sulfamic acid / urea-treated pulp) after the sulfonate treatment is dehydrated with a 300-mesh wire mesh colander so that the solid content of the pulp is in the range of 1 to 10%, and the solid content is 0.5 g. Pulp. Place the pulp in a centrifugal cup, perform suction filtration, and stop suction when water is drawn from the pulp surface. Then, centrifugal dehydration (3000 G, 15 minutes) was performed, and the water retention was calculated from the ratio of the weight of wet pulp on the mesh in the centrifugal cup to the weight of pulp after drying using the following formula. The internal temperature during the centrifugation was 20 ° C. ± 5 ° C.

Water retention (%) = 100 x (wet pulp weight (g) after centrifugation-dry pulp weight (g)) / dry pulp weight (g)

(Observation of fiber morphology using FE-SEM)
The surface observation of the pulp after the chemical treatment was carried out using FE-SEM (manufactured by JEOL Ltd., model number; JSM-7610). For the sample, the solvent of the fine fiber dispersion was replaced with t-butyl alcohol, and the sample was freeze-dried and coated with osmium for observation.

(Measurement of fiber orientation)
The FE-SEM image of the pulp was image-analyzed to evaluate the fiber orientation.
FiberOri8s03 was used as the image analysis software. This software is also used to academically evaluate the fiber orientation on the paper surface.

(Measurement of whiteness)
The whiteness was measured according to JIS P 8148: 2001 paper, paperboard and pulp-ISO whiteness (diffuse blue light reflectance).
As the sample used for the measurement, the pulp after the chemical treatment was washed with water and freeze-dried.
For the measurement of whiteness, the pulp of the prepared sample was set in an ISO whiteness meter (manufactured by Nippon Denshoku Kogyo Co., Ltd .: PF-10), and the whiteness was measured.

(Observation of fiber morphology and measurement of fiber width using SPM)
The nanocellulose fibers treated with the high-pressure homogenizer were prepared with pure water to a solid content concentration of 0.001 to 0.005% by mass, and spin-coated on a silica substrate coated with PEI (polyethyleneimine).
Observation of the nanocellulose fibers on the silica substrate was performed using a scanning probe microscope (manufactured by Shimadzu Corporation, model number; SPM-9700).
The fiber width was measured by randomly selecting 20 fibers in the observation image.

(Measurement of haze value and measurement of total light transmittance)
For the measurement of the haze value and the measurement of the total light transmittance, a measurement solution prepared by using pure water for nanocellulose fibers and having a solid content concentration of 0.5% by mass was used.
In the micronization treatment step, those prepared so that the solid content concentration (processed pulp solid content concentration) of the sulfamic acid / urea-treated pulp in the slurry supplied to the high-pressure homogenizer is 0.5% by mass are micro-treated. The solid content concentration of the nanocellulose fibers in the dispersion obtained later is also 0.5% by mass, which is the same. Therefore, this dispersion was directly used for measurement with the solid content concentration of the nanocellulose fibers set to 0.5% by mass without any adjustment.

A predetermined amount is separated from the prepared measurement solution, and an integrating spherical shape (ISN-470 manufactured by JASCO Corporation) is attached to a spectrophotometer (manufactured by JASCO Corporation, model number; V-570) to obtain the haze value. The measurement and total light transmittance were measured as follows. The measurement method was based on the method of JIS K 7105.
A quartz cell containing pure water was used as a blank measurement value, and the light transmittance of 0.5% by mass of the nanocellulose dispersion was measured. The measurement wavelength range was 380 to 780 nm.
The total light transmittance (%) and the haze value (%) were calculated from the numerical values obtained by the spectrophotometer using the attached calculation software.

The measurement solution used in the spectrophotometer corresponds to the dispersion in the method for producing sulfonated fine cellulose fibers of the present embodiment.

(Measurement of degree of polymerization)
According to JIS P 8215 (1998), the intrinsic viscosity (intrinsic viscosity) of the nanocellulose fiber was measured with reference to the method A of the intrinsic viscosity of the nanocellulose fiber. As a change at the time of measurement, pulp and nanocellulose fiber were used as raw materials in a solid content measurement experiment of 0.1 g, and the average value of three measurements was taken as the measured value. Then, from each intrinsic viscosity (η), the degree of polymerization (DP) of the nanocellulose fiber was calculated by the following formula. Since this degree of polymerization is the average degree of polymerization measured by the viscosity method, it is sometimes referred to as "viscosity average degree of polymerization".

DP = 1.75 × [η]

(Result of Experiment 1)
(Experimental results of sulfamic acid / urea-treated pulp)
Tables 1 and 2 are characteristic tables of sulfamic acid / urea-treated pulp fibers. Table 1 shows Examples 1 to 16, BL and Comparative Example 1. Table 2 shows Examples 17 to 22, BL and Comparative Example 2.

Table 1 is a characteristic table of sulfamic acid / urea-treated pulp fibers under the condition of drying before the heating reaction (conditions in the drying step) (Examples 1 to 16).
Table 2 is a characteristic table of sulfamic acid / urea-treated pulp fibers under the condition that the pulp fibers were not dried before the heating reaction (unconditional drying step) (Examples 17 to 22).

FIGS. 2 to 6 specifically show the characteristics of the sulfamic acid / urea-treated pulp fiber.
FIG. 2 shows the amount of sulfur introduced (mmol / g) and the degree of water retention (%) of the sulfamic acid / urea-treated pulp fiber obtained under the condition of the drying step, and the sulfamic acid / urea ratio of the reaction solution ((g / L)). It is a graph which showed the relationship with / (g / L)) (Examples 13 to 16, Comparative Example 1).
FIG. 3 shows the water retention (%) of the sulfamic acid / urea-treated pulp fiber obtained under no conditions in the drying step and the sulfamic acid / urea ratio ((g / L) / (g / L)) of the reaction solution. It is a graph which showed the relationship (Example 17-22, comparative example 2).
FIG. 4 (A) shows the pulp fiber length (mm) of the sulfamic acid / urea-treated pulp fiber obtained under the condition of the drying step and the sulfamic acid / urea ratio of the reaction solution ((g / L) / (g / L). )), And FIG. 4 (B) shows the fiber length retention rate (%) before and after the chemical treatment of the sulfamic acid / urea-treated pulp fibers obtained under the condition of the drying step and the reaction solution. It is a graph which showed the relationship with the sulfamic acid / urea ratio ((g / L) / (g / L)) of (Examples 13 to 16, Comparative Example 1).
FIG. 5 is a graph showing the relationship between the amount of sulfur introduced (mmol / g) and the reaction temperature of the sulfamic acid / urea-treated pulp fibers obtained under the condition of the drying step (Examples 1 to 12).
FIG. 6A is a graph showing the relationship between the fiber length (mm) of the sulfamic acid / urea-treated pulp fiber obtained under the condition of the drying step, the reaction temperature, and the treatment time, and FIG. 6B is a graph. It is a graph which showed the relationship between the fiber length maintenance rate (%), the reaction temperature, and the treatment time before and after the chemical treatment of the sulfamic acid / urea-treated pulp fiber obtained under the condition of the drying step (Examples 1 to 12). ..

From the experimental results, by adjusting the mixing ratio of urea in the concentration ratio of sulfamic acid and urea, the amount of sulfur introduced (mmol / g) is 0 regardless of "conditional drying process" or "unconditional drying process". It was confirmed that sulfamic acid / urea-treated pulp fibers (for example, see FIG. 2) adjusted to .56 mmol / g to 0.97 mmol / g could be prepared.

As shown in FIG. 2 or 3, the water retention rate is 250 by adjusting the mixing ratio of urea in the concentration ratio of sulfamic acid and urea regardless of “drying process conditional” or “drying process unconditional”. It was confirmed that the sulfamic acid / urea-treated pulp fiber controlled in the range of% to 4600% could be prepared. That is, it was confirmed that by adjusting the concentration ratio of sulfamic acid and urea, sulfamic acid / urea-treated pulp fibers in which the amount of sulfur introduced and the degree of water retention were controlled could be prepared.
From FIGS. 2 and 3, the amount of sulfur introduced and the degree of water retention of the sulfamic acid / urea-treated pulp fiber tended to be similar, and it was inferred that there was some relationship between the two. ..

As shown in FIG. 4, it was confirmed that a sulfamic acid / urea-treated pulp fiber having a longer fiber length than that of Comparative Example 1 in which urea was not mixed could be prepared. That is, it was confirmed that by mixing urea in the manufacturing process, sulfamic acid / urea-treated pulp fibers in which shortening of fibers by sulfamic acid was prevented could be prepared.
Moreover, it was confirmed that the sulfamic acid / urea-treated pulp fibers in which the fiber length after the reaction was maintained to be substantially the same as that before the reaction could be prepared.

As shown in FIGS. 5 and 6, it was confirmed that the sulfamic acid / urea-treated pulp fiber in which the amount of sulfur introduced and the fiber length were controlled could be prepared by adjusting the reaction temperature and the heating time.
As shown in FIG. 5, in order to increase the amount of sulfur introduced into the sulfamic acid / urea-treated pulp fiber to 0.5 mmol / g or more, it may be 15 minutes or more under the condition of 120 ° C. or 140 ° C. However, it was confirmed that under the condition of low temperature of 100 ° C., it should be 35 minutes or more.
Further, as shown in FIG. 6, it was confirmed that in order to increase the fiber length of the sulfamic acid / urea-treated pulp fiber, those under a low temperature condition are preferable.

FIG. 7 is a surface enlarged photograph (50,000 times) of a sulfamic acid / urea-treated pulp fiber (with a drying process, reaction conditions: temperature 120 ° C., time 25 minutes).
7 (A) to 7 (D) show sulfamic acid / urea ratios of 200/50 (1: 0.25), 200/100 (1: 0.5), 200/200 (1: 1), and 200, respectively. It is a surface enlarged photograph of / 500 (1: 2.5) (Examples 13 to 16).
FIG. 7 (E) is a surface enlarged photograph of NBKP (BL) shown as a comparative example.

The amounts of sulfur introduced into the sulfamic acid / urea-treated pulp fibers shown in FIGS. 7 (A) to 7 (D) are (A) 0.56 mmol / g, (B) 0.84 mmol / g, and (C) 0.97 mmol / g, respectively. , (D) was 0.65 mmol / g.
The water retention levels of the sulfamic acid / urea-treated pulp fibers shown in FIGS. 7A to 7D were (A) 980%, (B) 1920%, (C) 1120%, and (D) 250%, respectively.

Tables 3, 8 and 9 show the relationship between the sulfamic acid / urea-treated pulp fibers and the degree of orientation of the surface fibers (Examples 13 to 16, BL).
Table 3 shows the relationship between the orientation of the sulfamic acid / urea-treated pulp fiber and the surface fiber, and FIG. 8 shows the relationship between the orientation of the surface fiber of the sulfamic acid / urea-treated pulp fiber and the sulfamic acid / urea. It is a graph showing.

FIG. 9 is a surface enlarged photograph (100,000 times) of a sulfamic acid / urea-treated pulp fiber (with a drying step, reaction conditions: temperature 120 ° C., time 25 minutes) (Examples 13 to 16).
9 (A) to 9 (D) show sulfamic acid / urea ratios of 200/50 (1: 0.25), 200/100 (1: 0.5), 200/200 (1: 1), and 200, respectively. It is a surface enlarged photograph of / 500 (1: 2.5).
FIG. 9 (E) is a surface enlarged photograph of NBKP (BL) shown as a comparative example.
The orientations of the sulfamic acid / urea-treated pulp fibers shown in FIGS. 9A to 9D are (A) 1.18, (B) 1.04, (C) 1.10, and (D) 1.30, respectively. Met.

In this measurement method, it was judged that the degree of orientation (orientation strength) of 1.1 or less is non-oriented, 1.1 to 1.2 is slightly oriented, and 1.2 or more is strongly oriented. ..

From this experimental result, it is possible to prepare a sulfamic acid / urea-treated pulp fiber in which the orientation of the fiber on the surface is randomized by lowering the mixing ratio of urea in the reaction solution in the concentration ratio of sulfamic acid and urea. Was confirmed. On the contrary, it was confirmed that by increasing the mixing ratio of urea, sulfamic acid / urea-treated pulp fibers in a state in which the orientation of the fibers on the surface were arranged could be prepared. That is, it was confirmed that by adjusting the concentration ratio of sulfamic acid and urea, sulfamic acid / urea-treated pulp fibers capable of controlling the fiber orientation on the surface can be prepared.

In addition, from the results of this experiment, it was confirmed that the degree of orientation of the surface fibers of the sulfamic acid / urea-treated pulp fibers can be used as an index indicating the degree of fibrillation of the sulfamic acid / urea-treated pulp fibers. Since it was confirmed that the degree of orientation and the degree of water retention show a specific tendency when the sulfamic acid / urea ratio is around 200/100 (see, for example, FIGS. 2 and 8), the degree of water retention is adjusted. By doing so, it was confirmed that the fibrillation of the sulfamic acid / urea-treated pulp fiber could be controlled.

FIG. 10 is a diagram confirming the ease of defibration treatment of the sulfamic acid / urea-treated pulp fiber, and shows the result of using the sulfamic acid / urea-treated pulp fiber under the “conditional drying process” as a representative. It is a thing.
As shown in FIG. 10 (A), it was confirmed that sulfamic acid / urea-treated pulp fibers having an average fiber width of 20 nm or less can be obtained by defibrating 3 times (3 passes). On the other hand, fine fibers that have not been chemically treated (that is, NBKP of blank pulp) have an average fiber width of 30 nm to 50 nm even after 20 times of defibration (20 passes), and those having an average fiber width of 20 nm or less can be obtained. I couldn't.
The photograph of FIG. 10 shows the measurement status of the fiber width in the observed image by observing the fine fibers after defibration with an FE-SEM. A 100,000-fold magnified photograph was used to measure the fiber width. As a method of measuring the fiber width in the image (for example, the width of the fiber indicated by the white arrow in FIG. 10), two diagonal lines are drawn on the observation image, and two straight lines passing through the intersections of the diagonal lines are arbitrarily drawn. The width of the fibers intersecting these straight lines was visually measured. The average fiber width was determined from the average value of 50 fibers.

Table 4 shows the relationship between the sulfamic acid / urea-treated pulp fiber and the whiteness under the “conditional drying process”, and FIG. 11 is a graph showing the relationship between the sulfamic acid / urea ratio and the whiteness. (Examples 13 to 16, Comparative Example 1, BL).

From Table 4 and FIG. 11, it was confirmed that by mixing urea with the reaction solution, sulfamic acid / urea-treated pulp fibers in which the coloring of the fibers by sulfamic acid was suppressed could be prepared.
In addition, it was confirmed that sulfamic acid / urea-treated pulp fibers having controlled whiteness can be prepared by adjusting the mixing ratio of urea in the concentration ratio of sulfamic acid and urea.

(Experimental results of nanocellulose fiber)
Table 5 is a characteristic table of nanocellulose fibers under “conditional drying process” (Examples 23 to 39).
Table 6 is a characteristic table of nanocellulose fibers in the “drying step unconditional” (Examples 40 to 55).

Table 5 is a characteristic table of the nanocellulose fibers obtained under the conditions of drying (conditions under the drying process). In Table 5, Example 39 is obtained by preparing sulfamic acid / urea-treated pulp fibers under “drying step conditions” as in other examples (for example, Example 36), and then refining the pulp fibers. Further, in Table 5, since the sulfamic acid / urea ratio ((g / L) / (g / L)) of Example 39 and Example 36 are both 2: 1, they are adjacent to each other to confirm the relationship. Was displayed.
Table 6 is a characteristic table of the nanocellulose fibers obtained under the condition of no drying (unconditional drying step). In Table 6, the table below is a miniaturized version of Examples 17 to 20 in Table 2, and Examples 40 to 51 in the above table are the same as other Examples (for example, Example 17). Sulfamic acid / urea-treated pulp fibers are prepared under "unconditional drying process" and then refined.

12 to 14 show concrete characteristics of nanocellulose.
FIG. 12 shows the total light transmittance (%) and haze value (%) of the nanocellulose fibers obtained under the condition of the drying step and the sulfamic acid / urea ratio ((g / L) / (g / L) of the reaction solution. )) Is a graph showing the relationship with (Examples 35 to 38, Comparative Example 3).
FIG. 13 shows the total light transmittance (%) and haze value (%) of the nanocellulose fibers obtained under no conditions in the drying step and the sulfamic acid / urea ratio ((g / L) / (g / L) of the reaction solution. )) Is a graph showing the relationship with (Examples 52 to 55, Comparative Example 4).
FIG. 14 shows the degree of polymerization of the nanocellulose fibers obtained under the condition of the drying step (that is, the one corresponding to the average fiber length of the nanocellulose fibers) and the sulfamic acid / urea ratio of the reaction solution ((g / L) / (. It is a figure which showed the relationship with g / L)) (Example 35-38, BL, Comparative Example 3).

As Comparative Example 3 and Comparative Example 4, a comparative sample (sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/0) in which the reaction solution had a sulfamic acid concentration of 200 g / L and urea was not added was prepared. Prepared. The same operation as in the other experimental examples was performed except that urea was not added.

From the results of this experiment, as shown in Tables 5 and 6, it was confirmed that the average fiber width of the nanocellulose fibers could all be adjusted to 20 nm or less.
As shown in Tables 5, 6, 12, and 13, when the solid content concentration of the nanocellulose fibers in the measurement solution (that is, the dispersion) is adjusted to 0.5% by mass, all light transmission is transmitted. The rate (%) is 90% or more, and the haze value (%) is 42.7% and 23.9% in some cases, but all others are 20% or less. It was confirmed that 15% or less of nanocellulose fibers could be prepared in most cases. That is, regardless of "conditional drying process" or "unconditional drying process", the obtained nanocellulose fibers can improve the dispersibility in the dispersion and can prepare nanocellulose fibers having extremely high transparency. Was confirmed. The transparency of the dispersion is obtained by evaluating the transparency of the dispersion by the total light transmittance and the turbidity of the dispersion by the haze value. In other words, highly transparent nanocellulose fibers and highly water-retaining sulfamic acid, except when the pulp supplied to the reaction process is dry without moisture (that is, with a moisture content of less than 1%). / It was confirmed that urea-treated pulp fibers could be prepared.

In a commercially available resin film for which transparency is required, the total light transmittance (%) of the methacrylic film having high transparency is about 90%, and the haze value of the polyethylene film which is a general-purpose resin. Since (%) was about 20%, it was confirmed that the nanocellulose fibers obtained in the experiment had the same or higher quality as the conventional commercially available products.

As shown in FIG. 14, it was confirmed that the nanocellulose fibers could be prepared so as to have a degree of polymerization of 386 to 478. It was confirmed that this value was obtained under the condition of only sulfamic acid and could be higher than that of the nanocellulose fiber (Comparative Example B). That is, it was confirmed that nanocellulose fibers having an improved degree of polymerization (that is, fiber length) can be obtained by mixing urea in the reaction solution. In other words, it was confirmed that nanocellulose fibers that are easily entangled between the fibers can be prepared.
When the degree of polymerization was 400 and the axial length of one glucose molecule was about 5 Å (about 0.5 nm), it was confirmed that nanocellulose fibers having a fiber length of about 200 nm could be obtained.

Table 7 shows the experimental results when a compound similar to sulfamic acid was used as the reaction solution (Example 53, Comparative Example 5, BL).

In this experiment, sulfate (ammonium hydrogensulfate) was used as a compound similar to sulfamic acid. The experimental method was the same except that ammonium hydrogensulfate was used instead of sulfamic acid.
As shown in Table 7, in Comparative Example 5, the sulfate (ammonium hydrogensulfate) / urea-based pulp fiber could not be defibrated when the number of defibration was 3 times (3 passes).
In addition, Table 7 shows Example 53 of Table 6 for comparison.

From the results of this experiment, urea does not or does not perform the same function as the sulfamic acid / urea system (for example, function as a catalyst) in sulfonation using sulfate (ammonium hydrogensulfate). It was confirmed that it was not functioning sufficiently.
Therefore, in the sulfamic acid / urea system, the miniaturization efficiency can be improved and the degree of sulfonation can be improved as compared with the case of sulfonation using a sulfate (ammonium hydrogensulfate). Was confirmed.

<Experiment 2>
In Experiment 2, it was confirmed that by adjusting the water retention of the sulfamic acid / urea-treated pulp fiber, the sulfamic acid / urea-treated pulp fiber that can be easily defibrated can be prepared.

To evaluate the ease of defibration, the sulfamic acid / urea-treated pulp (Examples 13 to 16, Comparative Example 1) obtained in (Experiment 1) was prepared so that the solid content concentration was 0.2% by mass. The slurry was supplied to a high-pressure homogenizer and evaluated based on the fiber residual ratio contained in the dispersion liquid in which the prepared nanocellulose fibers were dispersed (Examples 56 to 59, Comparative Example 6).
In addition, the total light transmittance (%) and the haze value (%) at such solid content concentration were also confirmed.

The conditions for the high-pressure homogenizer were as follows.
First, preliminary defibration was performed using a high-pressure homogenizer (manufactured by Kos Nijuichi Co., Ltd., model number; N2000-2C-045 type). The preliminary defibration was performed at a defibration pressure of 10 MPa with two defibration cycles and at 50 MPa with one defibration frequency. Then, the slurry obtained by performing this preliminary defibration was subjected to a high-pressure homogenizer to prepare nanocellulose fibers. The defibration pressure at this time was set to 60 MPa, which is about half that of (Experiment 1).
As the device other than the high-pressure homogenizer, the device used in (Experiment 1) was used.
Further, in the measurement method of Experiment 2, the explanation overlapping with (Experiment 1) will be omitted.

(Fiber residual rate (%))
The fiber residual ratio (%) of the undefibrated fibers contained in the prepared dispersion containing the nanocellulose fibers was calculated based on the measured fibers in the solid content of 0.05 g before and after the defibration treatment.

The device used was a fiber tester (manufactured by Lorenzen & Betley Co., Ltd.).
First, a fiber that can be measured in 0.05 g of solid content from a slurry prepared by using the above apparatus to prepare a sulfamic acid / urea-treated pulp before defibration treatment so that the solid content concentration is 0.2% by mass. We measured how many of them existed.
Then, using the above-mentioned apparatus, it was measured how many measurable fibers were present in the solid content of 0.05 g from the dispersion liquid of the nanocellulose fibers after the defibration treatment.
Then, the fiber residual ratio (%) was calculated from the following formula.

Fiber residual rate (%) = (measured value after defibration treatment / measured value before defibration treatment) x 100

(Result of Experiment 2)
Tables 8 and 15 show the relationship between the water retention rate (%), the fiber residual rate (%), and the number of high-pressure homogenizer passes of the sulfamic acid / urea-treated pulp fibers prepared under the “drying process condition”. (Examples 56 to 59).
When the fiber residual ratio (%) was 1% or less, the fibers contained in the dispersion could not be visually confirmed.

As shown in Table 8 and FIG. 15, it was confirmed that the higher the water retention rate (%) of the sulfamic acid / urea-treated pulp fibers, the lower the fiber residual rate (%) (Examples 56 to 59).
In the sulfamic acid / urea-treated pulp in which the sulfamic acid / urea-treated pulp fibers having a water retention rate (%) of 980%, 1120% and 1920% are aggregated, the defibration pressure is 60 MPa or less and the number of defibration is once (1 pass). It was confirmed that nanocellulose fibers with high transparency can be obtained by the treatment.
Moreover, even in the case of sulfamic acid / urea-treated pulp in which sulfamic acid / urea-treated pulp fibers having a water retention rate (%) of 250% are aggregated, nanocellulose fibers having high transparency after being defibrated twice (2 passes). It was confirmed that

Further, as shown in Tables 9 and 16, if the water retention (%) of the sulfamic acid / urea-treated pulp fibers is higher than that of Comparative Example D (water retention 180%), the fiber is defibrated once (1 pass). It was confirmed that nanocellulose fibers having a high total light transmittance (%) could be prepared (Examples 56 to 59, Comparative Example 6).

As shown in FIG. 17, it was confirmed that nanocellulose fibers having a haze value (%) of 15% or less can be prepared by the treatment with two defibration times (2 passes). In particular, when the water retention (%) of the sulfamic acid / urea-treated pulp fiber is 1000% or more, nanocellulose fibers having a haze value (%) of 5% or less are prepared by one-time defibration (1 pass) treatment. It was confirmed that this was possible (Examples 56 to 59, Comparative Example 6).

In Comparative Example 6, the dispersion obtained after the defibration treatment was in a turbid state containing a large amount of precipitate. Then, as shown in FIGS. 16 and 17, the haze value (%) of Comparative Example 6 was almost 100%, and the total light transmittance (%) was 40% or less. Therefore, under this condition. It was confirmed that Comparative Example D could not be properly defibrated by defibration.
Further, even when defibration was performed by increasing the number of defibration (number of passes), sufficient defibration results could not be obtained in Comparative Example 6.

From the experimental results of Experiment 2, by adopting a manufacturing method in which urea is mixed with the reaction solution, sulfamic acid / urea can be easily defibrated even at a low defibration pressure not expected by the conventional technique. It was confirmed that treated pulp fibers could be prepared.
Moreover, the water retention (%) of the sulfamic acid / urea-treated pulp fiber is higher than that of Comparative Example 6 (water retention 180%), and the sulfur introduction amount of the sulfamic acid / urea-treated pulp fiber is 0.42 mmol / of the comparative example. It was confirmed that highly transparent nanocellulose fibers could be easily prepared if the amount was adjusted to be higher than g.
In particular, if the water retention (%) of the sulfamic acid / urea-treated pulp fiber is adjusted to 1000% or more, the haze value (%) can be easily obtained with a defibration pressure of 60 MPa or less and one defibration frequency (1 pass). It was confirmed that nanocellulose fibers having a value of 5% or less and having excellent transparency could be prepared.

<Experiment 3>
In Experiment 3, the effect of the solid content concentration of the sulfamic acid / urea-treated pulp fiber on the defibration treatment of the prepared nanocellulose fiber was confirmed.

In this experiment, a reaction solution having a sulfamic acid / urea ratio ((g / L) / (g / L)) of 200/100 (1: 0.5) was used and the above-mentioned production method (with drying step). Reaction conditions: Sulfamic acid / urea-treated pulp fibers (Example 14) prepared at a temperature of 120 ° C., a time of 25 minutes, and a water retention rate of 1920%) had solid content concentrations of 0.5% by mass and 0.2% by mass, respectively. The slurry prepared so as to be supplied to a high-pressure homogenizer. Then, the quality of the obtained nanocellulose fibers was evaluated by the total light transmittance (%), the haze value (%), and the number of undefibrated fibers after defibration (Examples 60 to 61).

The total light transmittance (%) and the haze value (%) were measured by the same method as in (Experiment 1).
The number of undefibrated fibers is measured in 0.05 g of solid content by measuring the undefibrated fibers in 0.05 g of solid content after the defibration treatment with a fiber tester (manufactured by Lorenzen & Bettley Co., Ltd.). The number of possible fibers was measured.

(Result of Experiment 3)
The experimental results of Experiment 3 are shown in Table 10 and FIG. 18 (Examples 60 to 61).
Table 10 and FIG. 18 confirm the solid content concentration of the sulfamic acid / urea-treated pulp fiber in the slurry supplied to the high-pressure homogenizer and the effect on the obtained nanocellulose fiber.

As shown in Table 10 and FIG. 18, the total light transmittance (%) was about 100% and the haze value (%) was 5% or less. In addition, the number of undefibrated fibers was 30 or less in each of the treatments with one defibration (1 pass), and there was a large difference in the solid content concentration (0.5% by mass and 0.2% by mass). Was not confirmed.
Therefore, the solid content concentration of the sulfamic acid / urea-treated pulp fibers in the slurry supplied to the high-pressure homogenizer affects the ease of defibration in the range of 0.2% by mass to 0.5% by mass. I was able to confirm that there was no such thing. Moreover, it was confirmed that the quality of the nanocellulose fibers prepared at these solid content concentrations does not affect the quality within this solid content concentration range.

<Experiment 4>
In Experiment 4, it was confirmed that the sulfur in the sulfamic acid / urea-treated pulp fibers and the nanocellulose fibers was caused by the sulfo group.

In Experiment 4, the state of sulfur in the sulfamic acid / urea-treated pulp fiber prepared by the same method as in (Experiment 1) was measured by a Fourier transform infrared spectrophotometer (FT-IR, JASCO Corporation). Manufactured by, model number: FT / IR-4200) and confirmed using the above-mentioned combustion ion chromatograph.
Further, the prepared sulfamic acid / urea-treated pulp fiber was micronized by the method of (Experiment 1) to prepare nanocellulose fiber, and the state of sulfur of the prepared nanocellulose fiber was measured by an electric conductivity meter (DKK CORPORATION). Confirmed using the company, CONDUCTIVITY METER, model number AOL-10).

In Experiment 4, a sulfamic acid / urea-treated pulp was prepared under the following conditions in the same manner as in (Experiment 1).
Reaction solution: Sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/200
The pulp and the reaction solution were brought into contact with each other and dried at 50 ° C. (“drying step conditional”). Then, the heating reaction was carried out under the conditions of 120 ° C. and 25 minutes. After the heating reaction, the reacted pulp was thoroughly washed until it became neutral to prepare a sulfamic acid / urea-treated pulp fiber.
In Experiment 4, the pulp after the heating reaction was washed by the following method so that the reaction solution physically adsorbed on the pulp fibers after the heating reaction did not exist.
First, the pulp was added to a saturated aqueous sodium hydrogen carbonate solution until the pulp after the heating reaction became neutral, and the mixture was stirred for 10 minutes to neutralize the pulp. Then, the neutralized pulp was washed with a large amount of pure water and dried to prepare a sulfamic acid / urea-treated pulp fiber (Example 62). The aggregate of the sulfamic acid / urea-treated pulp fibers is the sulfamic acid / urea-treated pulp.

On the other hand, Comparative Example 7 was prepared by the same method as in Experimental Example 4 including the washing method, except that the heating reaction step was not performed.

(FT-IR measurement)
The FT-IR measurement was performed by the ATR method.
The measurement conditions were a measurement wave number range of 600 to 4000 cm ^-1 , and the number of integrations was 100. As the sample, a sample washed after sulfonate treatment and dried at 105 ° C. was used.

(Measurement of electrical conductivity)
In the treatment with an ion exchange resin, a strongly acidic ion exchange resin (manufactured by Organo Corporation, Amber Jet 1024; conditioned) with a volume ratio of 1/10 is added to a slurry containing 0.2% by mass of nanocellulose fibers and shaken for 1 hour. Finally processed. Then, it was poured onto a mesh having a mesh size of 200 μm to separate the resin and the slurry.
In titration using alkali, the value of electrical conductivity indicated by the mixed solution of the nanocellulose fiber-containing slurry and the sodium hydroxide aqueous solution while adding 0.5 N sodium hydroxide aqueous solution to the nanocellulose fiber-containing slurry after ion exchange. The change in was measured.

(Nuclear magnetic resonance (NMR) measurement)
The NMR of the sulfamic acid / urea-treated pulp was measured.
For the measurement, the sulfamic acid / urea-treated pulp prepared in (Experiment 1) (sulfamic acid / urea ratio ((200 g / L) / (200 g / L)), sulfur introduction amount 0.97 mmol / g), "drying step" Conditional ”, Example 15) was used.

The NMR measurement conditions are as follows.
The measurement was performed by the HSQC method using adiabatic pulp using NMR (Agilent Technologies, Inc., model number Agent 400 DD2, resonance frequency 400 MHz) at a total number of times of 480 times. In addition, deuterated DMSO was used as an internal standard, and the central peak was adjusted to F1 axis (13C): 39.5 ppm and F2 axis (1H): 2.49 ppm. Analysis software (Vnmrj 4.2) manufactured by Agilent Technologies Co., Ltd. was used for data analysis.
After the sulfonate treatment, the washed and dried sulfamic acid / urea-treated pulp was pulverized with a ball mill to prepare pulverized pulp. As for the ball mill crushing conditions, a small planetary ball mill (P-7 manufactured by Frisch) was used, and the crushing treatment was performed three times at 600 rpm for 20 minutes.
The crushed pulp (30 g) was dispersed in a deuterated DMSO solvent (0.7 ml) and subjected to ultrasonic treatment for 30 minutes to prepare a sample for NMR measurement.
As an internal standard, deuterated DMSO (manufactured by Wako Pure Chemical Industries, Ltd., model number: dimethyl sulfoxide-d6) was used.
For the blank, filter paper (manufactured by ADVANTEC, circular qualitative filter paper model number: No. 2) was used as cotton cellulose, and the same treatment as the above-mentioned sulfamic acid / urea-treated pulp was performed and subjected to NMR measurement.

(Result of Experiment 4)
Table 11 shows the measurement results of the amount of sulfur introduced into the sulfamic acid / urea-treated pulp fiber measured by the combustion ion chromatograph (Example 62, Comparative Example 7).

As shown in Table 11, the amount of sulfur introduced in the sulfamic acid / urea-treated pulp fiber was 0.97 mmol / g, and the amount of sulfur introduced in Comparative Example 7 was 0.01 mmol / g.

From the results of this experiment, as shown in Comparative Example 7, it was confirmed that the sulfamic acid physically adsorbed on the pulp fibers could be washed away almost completely by washing. That is, it was confirmed that the sulfamic acid / urea-treated pulp fibers had almost no sulfur physically adsorbed due to adsorption of the reaction solution, unwashed residue, or the like.

Further, since the sulfur introduction amount of the sulfamic acid / urea-treated pulp fiber was 0.97 mmol / g even after washing, the sulfur contained in the sulfamic acid / urea-treated pulp fiber was not physically adsorbed but reacted. It was speculated that sulfamic acid in the liquid chemically reacted with the hydroxyl groups of the cellulose fibers constituting the sulfamic acid / urea-treated pulp fibers and existed as sulfur that could not be washed or removed.

FIG. 19 shows the measurement result of FT-IR.
From FIG. 19, in the sulfamic acid / urea-treated pulp fiber (Example 62), peaks derived from S = O and SO, which are considered to be derived from the sulfo group, are observed at around 1200 cm-1 and 800 cm-1, while they are observed. In Comparative Example 7, these peaks could not be confirmed.
From this experimental result, in the sulfamic acid / urea-treated pulp fiber, a sulfo group is introduced into the hydroxyl group of the cellulose fiber constituting the sulfamic acid / urea-treated pulp fiber, and therefore, FT-IR and combustion ion chromatograph measurement are performed. It was inferred that the sulfur content could be confirmed.

FIG. 20 shows the measurement result of the electric conductivity measurement.
From FIG. 20, it was confirmed that the nanocellulose fiber-containing slurry after ion exchange can be neutralized and titrated with an aqueous sodium hydroxide solution. The titration curve was also the same as that when the strong acid was neutralized with a strong base.
From this experimental result, it was suggested that a strong acid group bond was introduced into the nanocellulose fiber. Based on the measurement results of electrical conductivity, the amount of sulfo group introduced into the nanocellulose fiber was 1 mmol / g (the amount of NaOH dropped at the inflection point in FIG. 20 is the amount of solid content of the fine cellulose fiber used in the experiment. It was confirmed that it was almost the same as the measurement result (0.97 mmol / g) obtained by the combustion ion chromatography method (calculated by dividing by).

FIG. 21 shows the results of NMR measurement of sulfamic acid / urea-treated pulp fibers.
As shown in FIG. 21, since the peaks of carbon and hydrogen at the C6 position of cellulose in the cellulose fibers constituting the sulfamic acid / urea-treated pulp fiber are shifted to the low magnetic field side, the hydroxyl group at the C6 position is sulfonated. It was suggested that

Comparing the peaks of sulfamic acid / urea-treated pulp fibers (spectral diagram above FIG. 21) with the peaks of unmodified cellulose (cotton cellulose) (spectrum diagram below FIG. 21), cellulose was obtained in both measurement results. Peaks derived from carbon and hydrogen at the 6th position of the glucose unit constituting the above (C: around 60 ppm, H: peaks detected around 3.5 to 3.8 ppm) were detected. On the other hand, in the sulfamic acid / urea-treated pulp fiber, a peak not present in the unmodified cellulose was detected at a position on the lower magnetic field side than the peak derived from carbon and hydrogen at the 6-position. In this peak, the hydroxyl group at the 6-position of the glucose unit is sulfonated, so that the hydroxyl group bonded to the carbon at the 6-position is about C: 64 to 65 ppm and H: about 3.8 to 4.1 by chemical treatment. It is thought that this is due to the chemical shift to.
From these results, it was suggested that the hydroxyl group at the 6-position of the glucose unit constituting cellulose was sulfonated in the sulfamic acid / urea-treated pulp fiber.

When Ando et al. Esterified cellulose in coniferous wood, the esterified peaks derived from carbon and hydrogen at the C6 position had a lower magnetic field than the peaks derived from the unmodified C6 hydroxyl group of the glucose unit. Since it has been reported that it appears on the side (ACS Sustainable Chem. Eng. 2017, 5, 1755-1762), the sulfamic acid / urea-treated pulp fiber prepared by this production method also has a hydroxyl group at the 6-position of the glucose unit. Is sulfonated, which is considered to shift to the low magnetic field side as described above.

Further, as shown in (Experiment 1), the nanocellulose fibers prepared by finely treating the sulfamic acid / urea-treated pulp fibers prepared by this production method are "conditional in the drying process" and "unconditional in the drying process". Regardless, it had high transparency, and the fiber width was 20 nm or less under all conditions.
This is because the sulfamic acid / urea-treated pulp fibers prepared by this method have a high-density charge repulsion effect because the hydroxyl group at the C6 position exposed on the microfibrils is intensively sulfonated. Was speculated. Therefore, even when the sulfamic acid / urea-treated pulp fibers prepared by this production method are subjected to a simple defibration treatment, nanocellulose fibers exhibiting high transparency and high dispersibility could be produced. Think of it.

From the experimental results of Experiment 4, it was confirmed that only sulfur in which sulfur in the reaction solution was chemically bonded can be present in the sulfamic acid / urea-treated pulp fiber. Then, it was confirmed that this sulfur is a strongly acidic group derived from S = O and SO. In other words, it was confirmed that the measured sulfur was due to the sulfo group chemically bonded to the hydroxyl group of the cellulose fiber constituting the sulfamic acid / urea-treated pulp fiber.
Therefore, it was confirmed that the sulfamic acid / urea-treated pulp fiber prepared by this production method was introduced in a state where the sulfo group was chemically bonded to the hydroxyl group of the cellulose fiber constituting the sulfamic acid / urea-treated pulp fiber. did it.
Further, it was confirmed that in the sulfamic acid / urea-treated pulp fiber prepared by this production method, the hydroxyl group at the C6 position among the hydroxyl groups of the cellulose fibers constituting the sulfamic acid / urea-treated pulp fiber was sulfonated. That is, by using this production method, the sulfo group can be preferentially introduced into the hydroxyl group at the C6 position rather than the hydroxyl group at the C2 position or the C3 position in the cellulose fiber. Therefore, by using this production method, it is possible to prepare a pulp fiber in which dissolution and cleavage of the cellulose fiber are suppressed as compared with a pulp fiber in which a sulfo group is introduced into the hydroxyl groups at the C2 and C3 positions in the cellulose fiber. It was confirmed that it was possible to prepare pulp fibers capable of producing nano-cellulose fibers having high transparency by performing defibration treatment.

<Experiment 5>
In Experiment 5, it was confirmed that the sulfamic acid / urea-treated pulp fiber did not have a urethane bond based on urea in the reaction solution.

In Experiment 5, sulfamic acid / urea-treated pulp fibers were prepared by the same method as in (Experiment 4) (Example 63).
The nitrogen content in the prepared sulfamic acid / urea-treated pulp fibers was measured using an elemental analyzer (PerkinElmer Japan Co., Ltd., 2400II CHNS / O).
As a comparative example, the nitrogen content in untreated NBKP (BL) was measured using the above elemental analyzer.

(Result of Experiment 5)
Table 12 shows the measurement results of the nitrogen content in the sulfamic acid / urea-treated pulp fiber and NBKP (Example 63, BL).

As shown in Table 12, the prepared sulfamic acid / urea-treated pulp fiber (Example 63) did not show an increase in nitrogen content as compared with NBKP (BL).

From the experimental results of Experiment 5, it can be confirmed that the sulfamic acid / urea-treated pulp fibers prepared by this production method do not have urethane bonds introduced even when urea is used in the reaction solution in the chemical treatment step. It was.

Here, in the prior art, it has been reported that when urea is used during the chemical modification of pulp, urethane bonds such as carbamate are formed in the chemically modified pulp. It has been reported that the formation of this urethane bond improves the dispersibility of the cellulose fibers and improves the transparency of the nanocellulose dispersion obtained after defibration.
However, since the introduction of urethane bonds was not confirmed in the sulfamic acid / urea-treated pulp fibers, the urea in the reaction solution in this production method is a sulfamic acid / urea-treated pulp by a mechanism different from that of the conventional technique. It was presumed that it was acting on the fibers.
In other words, it was presumed that the urea used in the reaction solution of the chemical treatment step in this production method did not contribute to the improvement of cellulose defibration in sulfamic acid / urea-treated pulp fibers and the transparency in nanocellulose fibers. ..

<Experiment 6>
In Experiment 6, it was confirmed from the viewpoint of crystal morphology that the sulfamic acid / urea-treated pulp fibers suppressed damage to the fibers due to chemical treatment.
In (Experiment 1), it was confirmed that damage to the fiber due to chemical treatment was suppressed from the viewpoint of maintaining the fiber length.

In Experiment 6, the sulfamic acid / urea-treated pulp fiber was prepared under the following conditions in the same manner as in (Experiment 1).
Reaction solution: Sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/50
Reaction solution: Sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/100
Reaction solution: Sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/200
Reaction solution: Sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/500

The pulp and the reaction solution were brought into contact with each other and dried at 50 ° C. (“drying step conditional”). Then, the heating reaction was carried out under the conditions of 120 ° C. and 25 minutes. The pulp after the heating reaction was added to a saturated aqueous sodium hydrogen carbonate solution until it became neutral, and the mixture was stirred for 10 minutes to neutralize the pulp, and then the neutralized pulp was washed with a large amount of pure water. Then, it was dried using a freeze-dryer (manufactured by EYELA, model number: FDU-1200) to prepare a sulfamic acid / urea-treated pulp fiber (Examples 64-67).
In Experiment 6, a freeze-dryer was used because the crystal part may be damaged by heat and the original crystallinity may not be exhibited.

The crystal structure of the prepared sulfamic acid / urea-treated pulp fiber was measured using an X-ray diffractometer (manufactured by Rigaku Co., Ltd., model: Ultima IV). The crystallinity was determined by the Segal method.
As a comparative example, the crystal structure of the NBKP fiber prepared by freeze-drying the untreated NBKP (BL) was measured by the same method as the above method.

Conditions for X-ray diffractometer X-ray source: Copper tube voltage: 40 kV
Tube current: 40mA
Measurement range: Diffraction angle 2θ = 10 ° to 30 °
X-ray scan speed: 2 ° / min

Calculation of crystallinity With the diffraction intensity of 2θ = 10 ° to 30 ° as the baseline of the X-ray diffraction result, the diffraction intensity of the 002 surface of 2θ = 22.6 ° and the diffraction of the amorphous part of 2θ = 18.5 ° The crystallinity (%) was calculated from the strength by the following formula.
Crystallinity (%) = ((I22.6-I18.5) /I22.6) x 100
I22.6: 2θ = 22.6 °, diffraction intensity of 002 surface I18.5: 2θ = 18.5 °, diffraction intensity of amorphous part

(Result of Experiment 6)
Table 13 shows the crystallinity and crystal structure of the sulfamic acid / urea-treated pulp fibers (Examples 64-67, BL).
FIG. 22 shows a representative example of the X-ray diffraction result of the sulfamic acid / urea-treated pulp fiber (reaction solution: sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/100 treated. Example 65) is shown.

As shown in Table 13, it was confirmed that the crystallinity was as high as 60% or more regardless of which reaction solution was used to prepare the sulfamic acid / urea-treated pulp.
Further, from the X-ray diffraction result of FIG. 22, it was confirmed that the crystal structure of the sulfamic acid / urea-treated pulp retains the same type I as that of the untreated NBKP.

From the experimental results of Experiment 6, it was confirmed that the sulfamic acid / urea-treated pulp prepared by this production method had an suppressed effect on the crystal structure and crystallinity even when chemically treated. .. That is, a sulfamic acid / urea-treated pulp has been prepared in which damage to fibers has been confirmed to be suppressed from both the viewpoint of fiber length and the viewpoint of crystal morphology even when chemically treated. I was able to confirm that.
Therefore, the sulfamic acid / urea-treated pulp fiber prepared by this production method can introduce a sulfo group into the hydroxyl group of the cellulose fiber constituting the sulfamic acid / urea-treated pulp fiber by chemical treatment, and can be added to the fiber by chemical treatment. It was confirmed that the damage was properly suppressed.

<Experiment 7>
In Experiment 7, the relationship between the degree of polymerization and the degree of crystallinity before and after defibration of the sulfamic acid / urea-treated pulp fiber and the nanocellulose fiber prepared by this production method was confirmed.

Sulfamic acid / urea-treated pulp fibers and nanocellulose fibers were prepared by the same production method as (Experiment 1) (“drying step conditional”) (Examples 68 to 71).
The nanocellulose fiber was prepared by using a sulfamic acid / urea-treated pulp fiber using a high-pressure homogenizer (manufactured by Kos Nijuichi Co., Ltd., model number; N2000-2C-045 type) until the fiber became invisible.
The degree of polymerization was measured by the same method as that shown in (Experiment 1). The crystallinity was measured by the same method as that shown in (Experiment 6). The nanocellulose fiber was prepared by using a sulfamic acid / urea-treated pulp fiber with a high-pressure homogenizer (manufactured by Kos Nijuichi Co., Ltd., model number; N2000-2C-045 type) until the fiber became invisible.

For the X-ray diffraction measurement of the sulfamic acid / urea-treated pulp fibers, those having a crystallinity of 77.4% (Example 69) before defibration in Table 15 were provided. Further, for the X-ray diffraction measurement of the nanocellulose fibers, those having a crystallinity of 52.0% (Example 70) after defibration in Table 15 were provided.

(Result of Experiment 7)
The measurement results of the degree of polymerization before and after defibration are shown in Table 14 (Examples 68 to 71).
The crystallinity and crystal structure before and after defibration are shown in Table 15 (Examples 68 to 71, BL).
The X-ray diffraction results are shown in FIG. 23 (Example 69, Example 70).

From the experimental results in Table 14, it was confirmed that the degree of polymerization of the fibers was reduced by the defibration treatment, but when this production method was used, the degree of polymerization of the nanocellulose fibers after defibration was as high as 54% to 82%. It is expected that the fiber length of the nanocellulose fibers will be longer than the general level due to this.
Further, from the experimental results of FIG. 23, it was confirmed that the crystal structure remained unchanged as type I before and after the defibration treatment. Further, from the experimental results in Table 15, it was confirmed that the crystallinity, which was 70% or more before defibration, decreased to about 42.1 to 52.0% after defibration.
Therefore, it was confirmed that when the defibration treatment of this production method was used, the crystallinity of the fibers changed before and after the defibration while maintaining the crystal structure.

<Experiment 8>
In Experiment 8, the relationship between the total light transmittance (%) and haze value (%) of the nanocellulose fibers prepared by this production method and the viscosity and TI value was confirmed.

In Experiment 8, sulfamic acid / urea-treated pulp (sulfamic acid / urea ratio ((200 g / L) / (500 g / L)) prepared by the same production method as in (Experiment 1), sulfur introduction amount 0.65 mmol / g, It was obtained by supplying a slurry prepared with a water retention degree of 250%, "conditional drying step", and Example 16) so that the solid content concentration was 0.5% by mass to the high-pressure homogenizer used in (Experiment 2). The viscosity of the dispersion of nanocellulose fibers was measured using a B-type viscometer (LVDV-I Prime, manufactured by Eiko Seiki Co., Ltd.) (Examples 72 to 77).

The measurement conditions for viscosity measurement were as follows.
The rotation speed is 6 rpm, the measurement temperature is 25 ° C., the measurement time is 3 minutes, and the spindle is No. 64

The defibration conditions were as follows.
The defibration pressure by the high-pressure homogenizer is 30 MPa, and the number of passes in the defibration process is 5 defibration times (5 passes), 7 defibration times (7 passes), 9 defibration times (9 passes), and defibration. The number of times was 11 (11 passes), the number of defibration was 15 (15 passes), and the number of defibration was 20 (20 passes).

The total light transmittance (%) and haze value (%) of the nanocellulose fibers obtained for each number of passes were measured by the same method as in (Experiment 1).
In addition, the thixotropy index (TI value) of the obtained nanocellulose fibers was measured for each number of passes.
The TI value was calculated using the above-mentioned B-type viscometer at rotation speeds of 6 rpm and 60 rpm, and the respective viscosities were calculated by the following formulas.

TI value = (viscosity at 6 rpm) / (viscosity at 60 rpm)

In addition, the fiber morphology of the nanocellulose fibers after defibration was observed using SPM.
In the SPM measurement, the fiber morphology of the nanocellulose fibers at each number of defibration was measured using a scanning probe microscope by the same method as the method shown in (Experiment 1).

(Experimental result of Experiment 8)
The experimental results of Experiment 8 are shown in Table 16.
FIG. 24 shows, as a representative, an observation photograph of Example 37.

As shown in Table 16, the range of viscosity measurement was 11748 to 17846 mPa · s. The TI value was 6 to 8.
Further, as shown in FIG. 24, it was confirmed that the nanocellulose fibers after defibration had a small fiber width and the fiber length was maintained to a certain length.
From this experimental result, it was confirmed that the prepared nanocellulose fiber had a narrow fiber width, and the degree of polymerization and the fiber length of the fiber were maintained to some extent. That is, it was confirmed that the prepared nanocellulose fiber had a high aspect ratio.
Further, as shown in Table 16, nanocellulose having a very high transparency with a haze value of 22.7% or less even when the defibration treatment is performed at a low defibration pressure of 30 MPa by a high-pressure homogenizer. It was confirmed that the fiber could be prepared.
Therefore, from the experimental results of Experiment 8, it was confirmed that nanocellulose fibers having a narrow fiber width and a long fiber length can be prepared by using this production method. Moreover, it was confirmed that such nanocellulose fibers having extremely high transparency can be prepared at a very low defibration pressure of 30 MPa.

<Experiment 9>
In Experiment 9, the relationship between the fiber width and the transparency of the nanocellulose fibers prepared by this production method was confirmed.

In Experiment 9, the haze value and total light transmittance are measured for the effect on transparency when the fiber width of the nanocellulose fiber is adjusted to be larger than 20 nm and when it is adjusted to be 20 nm or less. Confirmed by.

Nanocellulose fibers having a fiber width of 20 nm or less are sulfamic acid / urea-treated pulp fibers prepared by the same manufacturing method as in (Experiment 1) (sulfamic acid / urea ratio ((200 g / L) / (200 g / L))). , Sulfur introduction amount 0.97 mmol / g, water retention degree 1120%, Example 15), "drying step conditional") was prepared so that the solid content concentration was 0.5% by mass in (Experiment 2). It was prepared by supplying it to the high-pressure homogenizer used (defibration pressure 60 MPa) (Example 78).
For nanocellulose fibers with a fiber width of 30 nm to 50 nm, a high-pressure homogenizer (20 passes at a defibration pressure of 130 MPa) using a slurry prepared by adjusting NBKP to a solid content concentration of 0.5% by mass in (Experiment 1). ) To prepare (Comparative Example 8).
The fiber width of the nanocellulose fiber was measured using SPM in the same manner as in (Experiment 1). The measurement at that time was performed in the dynamic mode.
The haze value (%) and the total light transmittance (%) were measured by the same method as shown in (Experiment 1).

(Result of Experiment 9)
The experimental results of Experiment 9 are shown in Table 17 (Example 78, Comparative Example 8).

As shown in Table 17, the haze value of the nanocellulose fibers prepared so as to be 20 nm or less (see FIG. 24) (Example 78) was 1.1%, which was significantly lower than 20%. The haze value of the one prepared so that the fiber width was larger than 30 nm (Comparative Example 8) was 50% or more. That is, it was confirmed that the fiber width greatly contributes to the transparency of the nanocellulose fiber, and the haze value (that is, transparency) fluctuates greatly when the fiber width is about 30 nm.
Here, in wood pulp, cellulose microfibrils having a diameter of about 3 nm are generally bundled to form a structure. Since the cellulose microfibrils are firmly bonded to each other by hydrogen bonds, it is not possible to defibrate the cellulose microfibrils by mechanical treatment alone. Therefore, in order to defibrate wood pulp in microfibril units, it is necessary to introduce a functional group even on the surface of cellulose microfibrils and use a chargeable repulsive force. In particular, the hydroxyl group at the C6 position of the cellulose microfibrils is arranged so as to protrude three-dimensionally (see FIG. 21).
Therefore, by using this production method, a sulfo group can be selectively introduced into the hydroxyl group at the C6 position arranged so as to protrude three-dimensionally, so that a pulp fiber that is easily defibrated can be produced. I think it was. Then, it is considered that by defibrating the pulp fibers using this production method, nanocellulose fibers having high dispersibility and high transparency could be prepared by charge repulsion.

<Experiment 10>
In Experiment 10, the influence of the heating method on the heating reaction was confirmed.

In Experiment 10, sulfamic acid / urea-treated pulp fibers were prepared by the same method as in (Experiment 1) except that the hot press method using a heat press machine (model number: AH-2003C) manufactured by AS ONE Corporation was used as the heating reaction. Was prepared (Example 79).
The nanocellulose fiber was prepared by the same method as in (Experiment 1) (Comparative Example 9).
The haze value (%) and total light transmittance (%) of the prepared nanocellulose fibers were measured by the same method as shown in (Experiment 1).

The conditions of the hot press method are as follows.
100 ml of the reaction solution (sulfamic acid / urea ratio ((200 g / L) / (200 g / L))) prepared in the same manner as in (Experiment 1) was uniformly sprayed onto 20 g of an NBKP sheet having a basis weight of 15 g / m ^2. , 50 ° C. (“drying step conditional”). Then, it is sandwiched between hot presses heated to 120 ° C. and the heating reaction is allowed to proceed for 5 minutes. After the heating reaction, neutralization, washing, and defibration treatment were performed in the same manner as in (Experiment 1).
In the defibration treatment, first, preliminary defibration was performed using a high-pressure homogenizer (manufactured by Kos Nijuichi Co., Ltd., model number; N2000-2C-045 type). The preliminary defibration was performed at a defibration pressure of 10 MPa with two defibration cycles and at 50 MPa with one defibration frequency. Then, the slurry obtained by performing this preliminary defibration was subjected to a high-pressure homogenizer to prepare nanocellulose fibers. The defibration pressure at this time was set to 60 MPa, which is about half that of (Experiment 1).

(Result of Experiment 10)
The experimental results of Experiment 10 are shown in Table 18 (Example 79, Comparative Example 9).

As shown in Table 18, it was confirmed that if the hot press method is used in the heating reaction of this production method, defibration can be appropriately performed even if the heating time is 5 minutes. Moreover, it was confirmed that the prepared nanocellulose fiber had excellent transparency.

<Experiment 11>
In Experiment 11, the maximum amount of sulfur introduced into the sulfamic acid / urea-treated pulp fiber and the nanocellulose fiber when the chemical treatment step in this production method was performed only once was confirmed.

20 g (dry weight) of pulp was added to 700 g of the reaction solution (sulfamic acid / urea ratio ((200 g / L) / (200 g / L))) prepared in the same manner as in (Experiment 1). That is, it was prepared so that 10 g of the reaction solution was supported as a solid content with respect to 1 g (dry weight) of pulp. The prepared pulp (10 g of the reaction solution (as a solid content) with respect to 1 g of pulp (dry weight)) was dried using the same dryer as in (Experiment 1) in which the temperature of the constant temperature bath was set to 50 ° C. "Drying process conditional").
Then, the dried pulp was placed in a dryer in which the temperature of the constant temperature bath was set to 160 ° C. in the same manner as in (Experiment 1), and a heating reaction was carried out for 60 minutes.
After the heating reaction, the pulp taken out from the dryer was put into a saturated aqueous sodium hydrogen carbonate solution, stirred for 10 minutes, and then washed with pure water until it became neutral to prepare a sulfamic acid / urea-treated pulp.
Next, the sulfamic acid / urea-treated pulp was defibrated using the same high-pressure homogenizer as in (Experiment 2) with a slurry prepared so that the solid content concentration was 0.5% by mass to prepare nanocellulose fibers. (Example 80).

The sulfur content in the pulp after the chemical treatment was measured by the same method as in (Experiment 1).
The haze value and the total light transmittance were measured by the same method as in (Experiment 1).

(Result of Experiment 11)
The experimental results of Experiment 11 are shown in Table 19 (Example 80).

As shown in Table 19, when this production method is used, when a reaction solution (solid content) is supported in an amount of 10 times that of 1 g of pulp, 1.7 mmol / g is applied to the sulfamic acid / urea-treated pulp fiber. It was confirmed that sulfur can be introduced.
From the results of Experiment 11, it is possible to control the amount of sulfur introduced into the sulfamic acid / urea-treated pulp fiber by controlling the amount of the reaction solution (solid content) supported, the reaction temperature, and the reaction time by using this production method. I was able to confirm that there was.
Further, as shown in Table 19, it was confirmed that the nanocellulose fibers obtained by defibrating the prepared sulfamic acid / urea-treated pulp fibers had high transparency.

<Experiment 12>
In Experiment 12, it was confirmed that heating was performed with pulp added to the reaction solution (Comparative Example 10).

In Experiment 12, 2 g (dry weight) of pulp was added to 100 ml of the reaction solution (sulfamic acid / urea ratio ((200 g / L) / (200 g / L))) prepared in the same manner as in (Experiment 1). , 100 mL of a slurry having a solid content concentration of 2% by mass of pulp was prepared.
This slurry was heated at 120 ° C. for 2 hours using an autoclave (manufactured by Tomy Seiko Co., Ltd., model number BS-235).

(Result of Experiment 12)
Since the pulp in the slurry taken out from the autoclave was visually grayed, it was presumed that the whiteness and water retention were very low.

<Experiment 13>
In Experiment 13, among the hydroxyl groups of the cellulose fibers constituting the sulfonated pulp, the effect of the introduction site of the sulfo group on the fibrillation property was confirmed.

The transparency and viscosity of the nanocellulose fibers were measured by the same methods as in (Experiment 1) and (Experiment 8), respectively.

In Experiment 13, as Comparative Examples 11 to 13, nanocellulose fibers in which a sulfo group was introduced into the C2-C3 position of the cellulose fibers were prepared based on a conventional method.

In Comparative Example 11, a solid content of 5 g of NBKP (pulp) manufactured by Marusumi Paper Co., Ltd. having a solid content concentration of 20% was added to an aqueous sodium periodate solution having a known concentration, and the final concentration was 38 mM of periodic acid and pulp solid content. The product prepared to have a concentration of 2% was heated in a water bath set at 55 ° C. for 3 hours. Then, it was washed with a large amount of pure water and filtered and dehydrated. Next, sodium periodate-treated pulp was added to an aqueous solution of sodium disulfite having a known concentration so that the solid content concentration was 2% (sodium disulfite at this time was adjusted to 28 mM), and the temperature was brought to room temperature. And left for 72 hours. After the reaction, it was washed with a large amount of pure water and used for the experiment. The defibration treatment was performed using a high-pressure homogenizer (manufactured by Yoshida Kikai Kogyo Co., Ltd., model number NV30-FA). As for the defibration conditions, the solid content concentration of the pulp was set to 0.5%, and the pulp was treated 4 times at 60 MPa.

Comparative Example 12 was carried out in the same manner as in Comparative Example 11 except that the concentrations of the periodic acid and the sodium disulfite aqueous solution were increased 1.5 times to 57 mM, and the reaction time in the sodium disulfite aqueous solution was set to 50 hours.

Comparative Example 13 was carried out in the same manner as in Comparative Example 11 except that the concentrations of the periodic acid and the aqueous sodium sulfite solution were increased 3.0 times.

In Example 81, sulfamic acid / urea-treated pulp was prepared under the following conditions in the same manner as in (Experiment 1).
Reaction solution: Sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/200
The pulp and the reaction solution were brought into contact with each other and dried at 50 ° C. (“drying step conditional”). Then, the heating reaction was carried out under the conditions of 120 ° C. and 25 minutes. After the heating reaction, the reacted pulp was thoroughly washed until it became neutral to prepare a sulfamic acid / urea-treated pulp fiber. The prepared sulfamic acid / urea-treated pulp fibers were adjusted to a solid content concentration of 0.5%, and defibrated using a high-pressure homogenizer (manufactured by Yoshida Kikai Kogyo Co., Ltd., model number NV30-FA) to prepare nanocellulose fibers.
As shown in Table 20, the defibration pressure and the number of passes were prepared as 4 passes in total, that is, the first 2 passes were 10 MPa, the next 1 pass was 50 MPa, and the last 1 pass was 60 MPa.

(Result of Experiment 13)
Table 20 shows the effect of the introduction position of the sulfo group on the defibration property (Example 81, Comparative Examples 11 to 13).

Table 20 shows the defibability of sulfamic acid / urea-treated pulp fibers having a sulfo group introduced at the C6 position (Example 81) and pulp having a sulfo group introduced at the C2-C3 position (Comparative Examples 11 to 13). Shows the effect of.
In pulp in which a sulfo group is introduced at the C2-C3 position, the transparency of the obtained nanocellulose fiber tends to increase as the amount of the sulfo group introduced increases (0.3 → 1.0 → 1.7 mmol / g). It was observed. On the other hand, the sulfamic acid / urea-treated pulp fiber (Example 81) in which the sulfo group was introduced at the C6 position was 1.0 mmol / g, and a transparent nanocellulose fiber was obtained.
Comparing Example 81 with the same amount of sulfo group introduced and Comparative Example 12, in Example 81, the nano having a total light transmittance of 96% or more and a haze of 20% or less when the sulfo group was introduced at the C6 position. While cellulose fibers were obtained, in Comparative Example 12 in which the sulfo group was introduced at the C2-C3 position, the haze value after defibration was 20% or more, and the transparency was low.
From these results, the sulfamic acid / urea-treated pulp fiber in which the C6 position of the hydroxyl groups of the cellulose fibers constituting the sulfonated pulp was sulfonated was more transparent than the one in which the C2-C3 position was sulfonated. It can be said that it is high and has excellent defibrillation properties.

<Experiment 14>
In Experiment 14, the effects of the sulfonation step and the defibration treatment step on the fiber shape and viscosity of the nanocellulose fibers were confirmed from the characteristics of the nanocellulose fibers obtained by various production methods.

The degree of polymerization and the degree of crystallinity of the nanocellulose fibers were measured in the same manner as in (Experiment 1) and (Experiment 6), respectively.

In the experiment, sulfamic acid / urea-treated pulp fibers were prepared under the following conditions in the same manner as in (Experiment 1).
Reaction solution (for Example 82): Sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/50, Reaction solution (for Example 83): Sulfamic acid / urea ratio ((g / g /) L) / (g / L)) = 200/100, reaction solution (for Example 84): sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/200, reaction solution (implementation) For Example 85): Sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/500
The pulp and the reaction solution were brought into contact with each other and subjected to a heating reaction under the same conditions as in (Experiment 13) (“drying step condition”) and then washed to prepare a sulfamic acid / urea-treated pulp fiber. Nanocellulose fibers were prepared from the prepared sulfamic acid / urea-treated pulp fibers using a high-pressure homogenizer in the same manner as in (Experiment 13).
A high-pressure homogenizer (manufactured by GEA Nirosoabi Co., Ltd., model number; Panda Plus 200) was used as a sample for measuring the degree of polymerization, and defibration was performed at 120 to 140 MPa for 3 passes.
A high-pressure homogenizer (manufactured by Kos Nijuichi Co., Ltd., model number; N2000-2C-045 type) was used as a sample for measuring the degree of crystallinity, and after defibrating twice at 10 MPa and once at 50 MPa, until the fibers disappeared at 60 MPa. Defibered.

As a comparative example, Comparative Examples 14 and 15 were prepared by the same manufacturing method as in Comparative Examples 11 and 13 of (Experiment 13). Comparative Example 16 was prepared by the following production method.
The degree of polymerization and crystallinity of the nanocellulose fibers of Comparative Examples 14 to 16 were measured in the same manner as in Examples.

In Comparative Example 16, sulfonated pulp and nanocellulose fibers were prepared as a sample whose introduction location was unknown by the following method. This method was carried out with reference to International Publication No. 2018/20295.
9 g (96%) of sulfuric acid and 11 g (99%) of urea were dissolved in 5 g of pure water to prepare a sulfonated solution. 23 g of this solution was impregnated with 10 g of NBKP having a water content of 10%. As NBKP, an NBKP sheet (moisture content of 50%) manufactured by Marusumi Paper Co., Ltd. was dried in a dryer heated to 105 ° C. and then allowed to stand in the air. The pulp impregnated with the sulfonated solution was allowed to stand overnight at room temperature and heated in a dryer at 150 ° C. for 15 minutes for sulfonation. After the sulfonate treatment, it was neutralized with sodium hydrogen carbonate, washed with a large amount of pure water, and used for the experiment. The defibration treatment was performed using a high-pressure homogenizer (manufactured by Yoshida Kikai Kogyo Co., Ltd., model number NV30-FA). Under the defibration conditions, the solid content concentration of the pulp was set to 0.5%, and the pulp was treated three times at 50 MPa.
The degree of polymerization and the degree of crystallinity were measured by the same method as in the examples.

(Result of Experiment 14)
Table 21 shows the degree of polymerization and crystallinity of pulp (sulfamic acid / urea-treated pulp fiber) and nanocellulose fiber before and after sulfonated and before and after defibration treatment.

It is generally said that the viscosity of nanocellulose fibers is affected by the fiber shape such as fiber length and crystallinity. Therefore, based on the finding that it is possible to develop the desired viscosity by setting the parameters in the fiber shape to appropriate values, the relationship between the fiber length and rigidity of the nanocellulose fiber and the increase in the viscosity of the dispersion liquid. It was confirmed. That is, with respect to the nanocellulose fibers that exhibit high viscosity of the dispersion, the fiber length was determined from the viewpoint of the degree of polymerization, and the rigidity of the fibers was determined from the viewpoint of the degree of crystallinity.

The above relationship will be described with reference to the results in Table 21.
First, the sulfonated pulp will be described.
In Comparative Examples, in Comparative Examples 14 and 15 which are the same production method, both the degree of polymerization and the degree of crystallinity were significantly reduced before and after sulfonation. Further, in Comparative Example 16 prepared by another method, the decrease was also large.
On the other hand, in Examples 82 to 85 obtained by the production method according to the present invention, no significant decrease was confirmed in the degree of polymerization and the degree of crystallinity before and after sulfonation. In Examples 82 to 85, the degree of polymerization maintenance rate after the reaction (degree of polymerization maintenance rate) was 50% or more in the degree of polymerization before and after sulfonation. That is, in Examples 82 to 85, the degree of polymerization ratio (degree of polymerization after reaction / degree of polymerization before reaction), which is the ratio of the degree of polymerization before and after the reaction, was 50% or more before and after sulfonation. The degree of polymerization ratio of this sulfonated pulp is synonymous with the degree of polymerization maintenance rate, which is the maintenance rate of the degree of polymerization after the reaction in the sulfonated pulp, and corresponds to the degree of polymerization ratio of the sulfonated pulp fibers in the embodiment.
Further, in Examples 82 to 85, the crystallinity maintenance rate after the reaction (crystallinity maintenance rate) was 80% or more in the crystallinity before and after the sulfonate. That is, in Examples 82 to 85, the crystallinity ratio (crystallinity after reaction / crystallinity before reaction), which is the ratio of crystallinity before and after the reaction, was 80% or more before and after sulfonation. .. The crystallinity ratio of this sulfonated pulp is synonymous with the crystallinity maintenance rate, which is the maintenance rate of the crystallinity after the reaction in the sulfonated pulp, and corresponds to the crystallinity ratio of the sulfonated pulp fibers in the embodiment. To do.

Next, the nanocellulose fiber will be described.
In Comparative Examples, in Comparative Examples 14 and 15 which are the same production method, no significant decrease in the degree of polymerization and crystallinity was confirmed before and after defibration. In addition, no significant decrease was confirmed in Comparative Example 16 prepared by another method.
On the other hand, in Examples 82 to 85 obtained by the production method according to the present invention, both the degree of polymerization and the degree of crystallinity of the sulfonated pulp before and after defibration were significantly reduced. In addition, defibration in the experiment is synonymous with defibration treatment or miniaturization treatment, and both notations mean the same. In addition, defibration may be referred to as defibration treatment or miniaturization treatment.
In Examples 82 to 85, in the polymerization before and after defibration, the degree of polymerization maintenance rate (polymerization degree maintenance rate) of the nanocellulose fibers after defibration is eventually higher than the degree of polymerization of the sulfonated pulp before defibration. Was less than 85%. That is, in Examples 82 to 85, the degree of polymerization ratio (the degree of polymerization after the pulverization treatment / the degree of polymerization before the pulverization treatment), which is the ratio of the degree of polymerization before and after the defibration treatment before and after the defibration treatment (miniaturization treatment). ) Was 85% or less. The degree of polymerization ratio of the nanocellulose fibers is synonymous with the degree of polymerization maintenance rate, which is the maintenance rate of the degree of polymerization of the nanocellulose fibers after defibration, and corresponds to the degree of polymerization ratio of the sulfonated fine cellulose fibers in the embodiment.
Further, in Examples 82 to 85, in the crystallinity before and after defibration, the maintenance rate of the crystallinity of the nanocellulose fibers after defibration (crystallinity maintenance rate) is the same as that of the sulfonated pulp before defibration. All were 75% or less with respect to the crystallinity. That is, in Examples 82 to 85, the crystallinity ratio (crystallinity after the defibration treatment / before the pulverization treatment), which is the ratio of the crystallinity before and after the defibration treatment (miniaturization treatment) before and after the defibration treatment (miniaturization treatment). Crystallinity) was 75% or less. The crystallinity ratio of the nanocellulose fibers is synonymous with the crystallinity maintenance rate, which is the maintenance rate of the crystallinity of the nanocellulose fibers after defibration, and the crystallinity ratio of the sulfonated fine cellulose fibers in the embodiment. Corresponds to.

Further, as shown in Table 20 of (Experiment 13), although the nanocellulose fibers of Comparative Examples 12 and 13 had some transparency, the viscosity was 1000 mPa · s or less, and it could not be said that the viscosity was high. On the other hand, in Example 81 obtained by the production method of the present invention, it was confirmed that the dispersion liquid exhibited high transparency and had a high viscosity of 10,000 mPa · s to 20,000 mPa · s. ..

In addition, from the results of this experiment (Experiment 14) and the previous experiment (Experiment 13), the reduction rates of the degree of polymerization and crystallinity before and after the reaction and before and after the defibration in each step (cellulose step and defibration treatment step) It was confirmed that it affects the viscosity of the obtained nanocellulose fiber. Such a phenomenon was well correlated with the place where the sulfo group was introduced.
As shown in Table 21, when Examples 82 to 85 in which the C6 position is intensively sulfonated and Comparative Examples 14 to 16 in which the C2-C3 position is sulfonated are compared, both of them are finally obtained nanos. The degree of polymerization and crystallinity of the cellulose fibers were significantly lower than those of the raw material pulp (pulp before sulfonation).
However, looking at the changes in each step, before and after the sulfonation reaction to the C6 position in Examples 82 to 85, the degree of polymerization and crystallinity of the sulfonated pulp after the reaction were higher than that of the raw material pulp before sulfonation. It did not change much compared to the degree and crystallinity. On the other hand, before and after the sulfonation reaction to the C2-C3 position of Comparative Examples 14 to 16, the degree of polymerization and crystallinity of the sulfonated pulp after the reaction were the degree of polymerization and crystallinity of the raw material pulp before sulfonation. Both were significantly reduced compared to the degree.
Further, when viewed before and after the defibration treatment, before and after the defibration of Examples 82 to 85 in which the sulfo group was introduced at the C6 position, the degree of polymerization and crystallinity of the nanocellulose fibers after defibration were before defibration. Both the degree of polymerization and the degree of crystallinity of the sulfonated pulp were significantly reduced. On the other hand, before and after defibration of Comparative Examples 14 to 16 in which the sulfo group was introduced at the C2-C3 position, the degree of polymerization and crystallinity of the nanocellulose fibers after defibration were different from those of the sulfonated pulp before defibration. There was not much change compared to the degree of polymerization and crystallinity of.

These facts are that the degree of polymerization and the degree of crystallization of the sulfonated nanocellulose fiber depend on the place where the sulfo group is introduced (C6 position, C2-C3 position) even if the final obtained values are the same. , It can be seen that the magnitude of the change in the value before and after each step (raw pulp → sulfonated pulp (sulfamic acid / urea-treated pulp fiber) → nanocellulose fiber) is different. That is, it is presumed that the influence on the fiber shape in each step (sulfonation, defibration treatment) differs depending on the place where the sulfo group is introduced. As a result, it was presumed that there was a difference in viscosity even in the dispersion liquid in which the obtained nanocellulose fibers were dispersed.
In summary, from the results of (Experiment 13) and (Experiment 14), the reaction of the sulfo group to the C2-C3 position shows the effect of lowering the viscosity of the nanocellulose fiber, whereas the reaction of the sulfo group to the C6 position is shown. It can be seen that the reaction leads to the result showing the effect of increasing the viscosity of the nanocellulose fiber.

Considering the above results from the viewpoint of fiber shape, it is generally said that the degree of polymerization is reduced by cutting and disintegrating the fiber length, and the degree of crystallinity is reduced by breaking and defibrating the fiber.
<Sulfonation reaction>
Looking at the changes after polymerization, in the sulfonated pulp of the present invention in which the sulfo group was introduced at the C6 position and the comparative example in which the sulfo group was introduced at the C2-C3 position, both the degree of polymerization decreased before and after sulfonation. It was. However, since the reduction rate of the comparative example in which the sulfo group was introduced at the C2-C3 position is larger than that of the sulfonated pulp of the present invention in which the sulfo group is introduced at the C6 position, the comparative example is the sulfonate of the present invention. It is presumed that the fibers are cut and broken more than the pulp.
Looking at the change in crystallinity, this also decreases as in the degree of polymerization. However, since the comparative example in which the sulfo group was introduced at the C2-C3 position was significantly reduced as compared with the sulfonated pulp of the present invention in which the sulfo group was introduced at the C6 position, the comparative example moved to the C2-C3 position. It was speculated that the cause was that the fibers were damaged by the chemical reaction of sulfonated and the crystalline region was broken.
<Miniaturization processing>
Before and after the defibration step, the nanocellulose fiber (sulfonated nanocellulose fiber) of the present invention in which the sulfo group was introduced at the C6 position has a degree of polymerization and a crystallinity as compared with the comparative example in which the sulfo group is introduced at the C2-C3 position. Both were greatly reduced. It is considered that this phenomenon is caused by the mechanical force of the defibration treatment, which promotes the defibration of the fibers and reduces the degree of polymerization and crystallinity of the nanocellulose fibers after defibration. That is, in the nanocellulose fiber of the present invention in which the sulfo group is introduced at the C6 position, the degree of polymerization and the degree of crystallinity in the sulfonated step do not change so much and decrease in the defibration step. It is considered that the decrease in crystallinity is mainly due to the influence of defibration. On the other hand, in the comparative example in which the sulfo group was introduced at the C2-C3 position, both the degree of polymerization and the degree of crystallinity in the sulfonate step were significantly reduced, so that the fibers had already collapsed at this time, and as a result, the defibration treatment was performed. It is probable that the decrease in the degree of polymerization and the degree of crystallinity before and after was small.

In the results of Comparative Example 16 in Table 21, the degree of polymerization and the degree of crystallinity were significantly reduced before and after the sulfonation reaction as in Comparative Examples 14 and 15 in which the sulfo group was introduced into the C2-C3 position. The maintenance rates before and after defibration showed high values. From this, it is presumed that the sulfo group was preferentially introduced at the C2-C3 position rather than the C6 position in the production method of Comparative Example 16. As a result, in the production method of Comparative Example 16, as in the other Comparative Examples, as shown in Table 20 of (Experiment 13), only nanocellulose fibers having a low viscosity could be obtained as the dispersion liquid. It is inferred that.

That is, it was confirmed that in the sulfonated pulp, the introduction location of the sulfo group (C6 position or C2-C3 position) can be grasped based on the amount of change in the degree of polymerization and the degree of crystallinity before and after the sulfonate reaction. .. Then, it was confirmed that the introduction location of the sulfo group (C6 position or C2-C3 position) in the sulfonated nanocellulose fiber can be grasped based on the amount of change in the degree of polymerization and the degree of crystallinity before and after the defibration treatment.
Specifically, if any of the following conditions is satisfied, it can be determined that the pulp is a sulfonated pulp or a sulfonated nanocellulose fiber in which a sulfo group is introduced at the C6 position.
(A) The degree of polymerization of the sulfonated pulp after the reaction in the reaction step of sulfonate is 50% or more in the degree of polymerization ratio (degree of polymerization after reaction / degree of polymerization before reaction) with respect to the pulp before reaction. is there.
(B) The crystallinity of the sulfonated pulp after the reaction in the reaction step of sulfonation is the crystallinity ratio (crystallinity after reaction / crystallinity before reaction) with respect to the pulp before reaction. It is 80% or more.
(C) The degree of polymerization of the nanocellulose fibers after the defibration treatment (fine treatment) of the sulfonated pulp is the degree of polymerization ratio (the degree of polymerization after the fine treatment / the degree of polymerization after the fine treatment) with respect to the sulfonated pulp before the defibration treatment. The degree of polymerization before the micronization treatment) is 85% or less.
(D) The crystallinity of the nanocellulose fibers after the defibration treatment (fine treatment) of the sulfonated pulp is the crystallinity ratio (crystals after the fine treatment) with respect to the sulfonated pulp before the defibration treatment. The degree of conversion / crystallinity before the finening treatment) is 75% or less.
Then, by using this production method, the sulfonation reaction to the C2-C3 position is suppressed, and the sulfonated pulp and the sulfonated nanocellulose fiber in which the C6 position is mainly reacted can be obtained. In particular, the nanocellulose fibers obtained by this production method have high transparency and / or high viscosity in the dispersion liquid when dispersed in a solution.

As described above, by using this production method, it is possible to provide nanocellulose fibers for use in which the dispersion liquid exhibits high viscosity.
In particular, the degree of polymerization ratio and / or crystallinity ratio before and after the reaction in the sulfonate reaction, and the degree of polymerization ratio and / or crystallinity ratio before and after defibration (before and after the pulverization treatment) when preparing the nanocellulose fiber. If it is prepared so as to be within the above range, it is possible to provide nanocellulose fibers in which the dispersion liquid can exhibit high viscosity in a state of being dispersed in the solution.
Further, when the solution to be dispersed itself has transparency, it is possible to provide nanocellulose fibers capable of exhibiting high viscosity of the dispersion while maintaining the transparency of the dispersion. it can.
The sulfonated pulp obtained by this production method has a predetermined amount of sulfur introduced, a water retention level equal to or higher than a predetermined value, and nanocellulose fibers (sulfone) obtained by introducing a sulfo group into the C6 position after defibration. It was confirmed that it is important in chemical fine cellulose fiber). Then, it was confirmed that the obtained nanocellulose fiber (sulfonated fine cellulose fiber) has a predetermined amount of sulfur introduced and the introduction of the sulfo group into the C6 position is important for increasing the viscosity of the dispersion liquid. ..

The sulfonated pulp fiber, derivative pulp, sulfonated fine cellulose fiber, sulfonated fine cellulose fiber manufacturing method and sulfonated pulp fiber manufacturing method of the present invention are various in the industrial field, the food field, the medical field, the cosmetic field and the like. It can be suitably used for many purposes in the field, and can also be suitably used as a raw material for composite materials used in these fields.

Claims (26)

Pulp fiber for fine cellulose fiber used to increase the viscosity of dispersion liquid.
The pulp fiber is
A part of the hydroxyl group of the cellulose fiber is replaced with a sulfo group.
While maintaining the fiber shape, the amount of sulfur introduced due to the sulfo group is higher than 0.42 mmol / g, and the water retention of the pulp fiber is 250% or more.
A sulfonated pulp fiber, wherein the hydroxyl group at the C6 position of at least a part of the glucose units constituting the cellulose fiber is substituted with the sulfo group. The pulp fiber is
The sulfonated pulp fiber according to claim 1, which has a cellulose type I crystal structure as a crystal structure, has a crystallinity of 70% or more, and has a degree of polymerization of 400 or more. Pulp consisting of multiple fibers
The plurality of fibers
A derivative pulp comprising the sulfonated pulp fiber according to claim 1 or 2. Cellulose fiber is a finely divided fine cellulose fiber,
This is for increasing the viscosity of the dispersion liquid in which the fine cellulose fibers are dispersed.
The fine cellulose fiber is
A part of the hydroxyl group is replaced with a sulfo group, the amount of sulfur introduced due to the sulfo group is higher than 0.42 mmol / g, and the average fiber width is 20 nm or less.
The hydroxyl group at the C6 position of at least a part of the glucose units constituting the cellulose fiber is substituted with the sulfo group.
The viscosity measured by rotating the dispersion liquid dispersed in water at a solid content concentration of 0.5% by mass at 20 ° C., rotation speed 6 rpm, and 3 minutes using a B-type viscometer is 10,000 mPa · s. The sulfonated fine cellulose fiber characterized by the above. Fine cellulose fibers
The sulfonated fine cellulose fiber according to claim 4, wherein the haze value in the dispersion liquid dispersed in water at a solid content concentration of 0.5% by mass is 20% or less. The sulfonated fine cellulose fiber according to claim 4 or 5, wherein the total light transmittance of the dispersion liquid dispersed in water at a solid content concentration of 0.5% by mass is 90% or more. The fine cellulose fiber is
The sulfonated fine cellulose fiber according to claim 4, 5 or 6, which has a cellulose type I crystal structure as a crystal structure, has a crystallinity of 55% or less, and has a degree of polymerization of 500 or less. The fine cellulose fiber is
The sulfonated fine cellulose fiber according to claim 4, 5, 6 or 7, wherein the sulfonated pulp fiber according to any one of claims 1 or 2 is made finer. A method for producing a sulfonated pulp fiber in which the hydroxyl group at the C6 position of at least a part of glucose units constituting the cellulose fiber is replaced with the sulfo group.
It includes a chemical treatment step of chemically treating the pulp.
The chemical treatment process
A contact step of contacting the pulp fibers constituting the pulp with a reaction solution prepared by dissolving sulfamic acid and urea in water.
The non-absolutely dry pulp after the contact step is supplied to the reaction step, and in the reaction step, a step of introducing a sulfo group into a part of the hydroxyl groups of cellulose constituting the pulp fiber is performed in order, and in the reaction step. ,
A step of heating the pulp fibers in contact with the reaction solution after the contact step at a reaction temperature of 100 ° C. to 180 ° C. and a reaction time of 1 minute or more to proceed the reaction is included.
The degree of polymerization of the obtained sulfonated pulp fiber
A method for producing a sulfonated pulp fiber, wherein the degree of polymerization ratio before and after the reaction (degree of polymerization after the reaction / degree of polymerization before the reaction) is 50% or more. The method for producing a sulfonated pulp fiber according to claim 9, wherein the degree of polymerization of the sulfonated pulp fiber obtained after the reaction is 400 or more. The crystallinity of the sulfonated pulp fiber obtained after the reaction is
The method for producing a sulfonated pulp fiber according to claim 9 or 10, wherein the crystallinity ratio before and after the reaction (crystallinity after the reaction / crystallinity before the reaction) is 80% or more. The method for producing a sulfonated pulp fiber according to claim 9, 10 or 11, wherein the crystallinity of the sulfonated pulp fiber obtained after the reaction is 70% or more. The reaction solution is
The sulfonated pulp fiber according to claim 9, 10, 11 or 12, wherein sulfamic acid and urea are contained in a concentration (g / L) ratio of 4: 1 to 1: 2.5. Manufacturing method. The method for producing a sulfonated pulp fiber according to claim 9 to 13, wherein the non-absolutely dry pulp supplied to the reaction step is in a water-containing state. The method for producing a sulfonated pulp fiber according to claims 9 to 14, wherein the non-absolutely dry pulp supplied to the reaction step has a water content of 1% or more. The method for producing a sulfonated pulp fiber according to claims 9 to 15, further comprising a washing step of washing the pulp after the reaction step. This is a method for producing a sulfonated fine cellulose fiber in which the hydroxyl group at the C6 position of at least a part of the glucose units constituting the cellulose fiber is substituted with the sulfo group.
It is a method of sequentially performing a chemical treatment step of chemically treating the pulp and a miniaturization treatment step of refining the pulp after the chemical treatment step.
The pulp after the chemical treatment step contains sulfonated pulp fibers produced by the production method according to any one of claims 8 to 14.
In the miniaturization processing step,
The step of finely dividing the pulp containing the sulfonated pulp fiber in a state of being dispersed in a water-soluble solvent so that the solid content concentration becomes 0.1% by mass to 20% by mass is included.
The degree of polymerization of the obtained sulfonated fine cellulose fiber is 85% or less in the degree of polymerization ratio (degree of polymerization after micronization treatment / degree of polymerization before micronization treatment) before and after micronization. Method for producing cellulose fiber. The method for producing a sulfonated fine cellulose fiber according to claim 17, wherein the degree of polymerization of the sulfonated fine cellulose fiber obtained after the fine treatment is 500 or less. The crystallinity of the sulfonated fine cellulose fibers after the micronization treatment is
The sulfonated fine cellulose fiber according to claim 17 or 18, wherein the crystallinity ratio before and after the refinement (crystallinity after the refinement treatment / crystallinity before the refinement treatment) is 75% or less. Manufacturing method. The method for producing a sulfonated fine cellulose fiber according to claim 17, 18 or 19, wherein the crystallinity of the sulfonated fine cellulose fiber obtained after the fine treatment is 55% or less. This is a method for producing sulfonated fine cellulose fibers in which pulp containing a plurality of pulp fibers is subjected to a micronization treatment step and the hydroxyl group at the C6 position of at least a part of glucose units constituting the cellulose fibers is replaced with the sulfo group. ,
The plurality of pulp fibers
The sulfonated pulp fiber produced by the production method according to any one of claims 9 to 16 is contained.
In the miniaturization processing step,
The step of finely dividing the pulp containing the sulfonated pulp fiber in a state of being dispersed in a water-soluble solvent so that the solid content concentration becomes 0.1% by mass to 20% by mass is included.
The degree of polymerization of the obtained sulfonated fine cellulose fiber is 85% or less in the degree of polymerization ratio (degree of polymerization after micronization treatment / degree of polymerization before micronization treatment) before and after micronization. Method for producing cellulose fiber. The method for producing a sulfonated fine cellulose fiber according to claim 21, wherein the degree of polymerization of the sulfonated fine cellulose fiber obtained after the fine treatment is 500 or less. The crystallinity of the sulfonated fine cellulose fibers after the micronization treatment is
The sulfonated fine cellulose fiber according to claim 21 or 22, wherein the crystallinity ratio before and after the refinement (crystallinity after the refinement treatment / crystallinity before the refinement treatment) is 75% or less. Manufacturing method. The method for producing a sulfonated fine cellulose fiber according to claim 21, 22 or 23, wherein the crystallinity of the sulfonated fine cellulose fiber obtained after the fine treatment is 55% or less. In the miniaturization processing step
The method for producing a sulfonated fine cellulose fiber according to claim 21, 22, 23 or 24, wherein the sulfonated pulp fiber has a water retention rate of 250% or more. The sulfonated fine cellulose fiber obtained after the micronization treatment is
The sulfonated fine cellulose fiber is measured by rotating the sulfonated fine cellulose fiber in a dispersion liquid in which the solid content concentration is 0.5% by mass by rotating at 20 ° C., a rotation speed of 6 rpm, and 3 minutes using a B-type viscometer. The method for producing a sulfonated fine cellulose fiber according to claims 21 to 25, which has a viscosity of 10,000 mPa · s or more.