WO2015087868A1

WO2015087868A1 - Cellulose fibers and method for producing same, ultrafine cellulose fiber dispersion and method for producing same, and method for producing ultrafine cellulose fibers

Info

Publication number: WO2015087868A1
Application number: PCT/JP2014/082533
Authority: WO
Inventors: 明磯貝; 賢志高市
Original assignee: 国立大学法人東京大学
Priority date: 2013-12-10
Filing date: 2014-12-09
Publication date: 2015-06-18
Also published as: JP2015113376A

Abstract

Provided is, for example, a method for producing cellulose fibers, which includes: an oxidation step of obtaining cellulose oxide fibers by oxidizing a cellulosic raw material in a reaction liquid that contains an N-oxyl compound and a co-oxidizing agent; a reduction step of obtaining reduced cellulose oxide fibers by reducing the cellulose oxide fibers in a reaction liquid that contains a reducing agent; and a drying step of drying the reduced cellulose oxide fibers. Cellulose fibers obtained by drying the reduced cellulose oxide fibers can be finely dispersed in a solvent.

Description

Cellulose fiber and production method thereof, fine cellulose fiber dispersion and production method thereof, and production method of fine cellulose fiber

The present invention relates to a cellulose fiber that can be finely dispersed in a solvent even after being dried, a fine cellulose fiber dispersion using the cellulose fiber as a raw material, a fine cellulose fiber thereof, a molded article comprising the fine cellulose fiber, and these It relates to a manufacturing method.

Fine cellulose fibers (hereinafter sometimes referred to as “cellulose nanofibers”), which are nano-sized materials, use cellulose, an abundantly existing biomass, as an oxidation catalyst using N-oxyl compounds as an oxidation catalyst. And then finely dispersed (hereinafter referred to as “nanodispersion”) by mechanical fibrillation treatment that imparts a shearing force in water to the oxidized cellulose (hereinafter sometimes referred to as “oxidized cellulose fiber”). Sometimes obtained). The oxidized cellulose nanofiber dispersion in which the oxidized cellulose fibers are nano-dispersed can be used as a thickening agent as it is or in the form of a gel combined with other materials. In addition, a material such as a sheet, a film, a foam, and an airgel can be produced by drying the oxidized cellulose nanofiber dispersion as it is or by combining it with another material (for example, Patent Documents). 1). The oxidized cellulose nanofiber is a bio-based nanofiber with a uniform width and a high aspect ratio, and has an excellent nanodispersibility in water due to a large specific surface area, high strength, and introduced carboxyl groups. There are features. Therefore, it is expected to be used in various fields such as an oxygen barrier film, a general-purpose plastic reinforcing material, a medical material, a cell culture substrate, a catalyst carrier, an adsorbent, and a separating material.

However, the aqueous dispersion of oxidized cellulose nanofibers (hereinafter sometimes referred to as “oxidized cellulose nanofiber dispersion” or “cellulose nanofiber dispersion”) has a solid content concentration of 0.1% by mass to 5%. Mass% is very low. Therefore, when transporting the oxidized cellulose nanofiber dispersion used for producing a product using the oxidized cellulose nanofiber, there is a problem that a large amount of water is transported and the cost for transport is high. In addition, when the oxidized cellulose nanofiber dispersion is stored, there is a problem that it must be refrigerated or treated with a preservative as a countermeasure against microorganisms.

As a countermeasure to the above problem, it is conceivable to transport the oxidized cellulose fiber dried and having a solid content concentration increased to 90% or more. However, even when a gentle drying method such as freeze drying is used, once dried, there is a problem that a cellulose nanofiber dispersion cannot be produced even under severe dispersion treatment conditions. .
If the nano-dispersion is not possible, there is a problem that the characteristics of the oxidized cellulose nanofiber such as uniform ultra-fine width, high aspect ratio, gel and film transparency are not exhibited.

As another countermeasure, fibrous oxidized cellulose before defibration and nano-dispersion treatment (width 0.01 mm to 0.06 mm, length 0.1 mm to 5 mm, wood cellulose fiber before oxidation treatment) Squeezed in the washing and filtration process, and the solid concentration was raised to about 10% to 40% (that is, containing 90% to 60% water) in an undried state. It is conceivable to carry. If it is the said undried oxycellulose, a cellulose nanofiber dispersion can always be manufactured by the fibrillation process in water. However, there is still a problem that the amount of water is still large even in an undried state, and the cost for transportation is high, and that preservative measures during storage are necessary.

In addition, as a method for producing a thickening cellulose fiber that can be easily redispersed in water, an aqueous cleaning solution containing 50 to 75% of a polar solvent other than water and a cellulose after oxidation has been used, and a pH of 5. A method of drying after purification under conditions of 5 or more has been proposed (for example, see Patent Document 2). However, the thickening cellulose fiber obtained by the above proposal has low transparency of the dispersion and cannot be said to be sufficiently dispersed, and repeated washing and drying using a polar solvent is an environmental burden. From the viewpoint of cost and cost, there is a problem that it cannot be said that it is suitable for practical use.

Therefore, even if it is once dried, it can be finely dispersed in a solvent in the same manner as when prepared from an undried state, and the cost for transportation can be reduced. The current situation is that there is a strong demand for rapid development of a manufacturing method that can be easily manufactured with a small load.

Japanese Patent No. 4998981 JP 2013-104133 A

This invention makes it a subject to solve the said various problems in the past and to achieve the following objectives. In other words, the present invention is a cellulose that can be finely dispersed in a solvent, even when it is once dried, as in the case of being prepared from an undried state, can reduce transportation costs, and has excellent storage stability. Fiber, manufacturing method of cellulose fiber which can easily manufacture cellulose fiber with small environmental load, fine cellulose fiber dispersion using the cellulose fiber and manufacturing method thereof, and using the fine cellulose fiber dispersion It aims at providing the manufacturing method of a fine cellulose fiber.

Means for solving the problems are as follows. That is,
<1> An oxidation step in which an oxidized cellulose fiber is obtained by oxidizing a cellulosic raw material in a reaction solution containing an N-oxyl compound and a co-oxidant;
A reduction step of reducing the oxidized cellulose fibers in a reaction solution containing a reducing agent to obtain reduced oxidized cellulose fibers;
A drying step of drying the reduced oxidized cellulose fiber,
The cellulose fiber obtained by drying the reduced oxidized cellulose fiber can be finely dispersed in a solvent.
<2> A cellulose fiber produced by the production method according to <1> and capable of being finely dispersed in a solvent.
<3> Cellulose fibers that can be finely dispersed in a solvent after drying,
After drying the cellulose fiber at 105 ° C. for 3 hours, the cellulose fiber is diluted with water to a concentration of 0.1% by mass to obtain a 40 mL dispersion, and the dispersion is placed in a 50 mL container. After defibrating for 2 minutes at 7,500 rpm using a cylindrical homogenizer, when the fiber is defibrated for 8 minutes with an ultrasonic homogenizer while cooling around the vessel with ice water, the light transmittance at a wavelength of 600 nm of the dispersion is It is a cellulose fiber characterized by having a birefringence of 80% or more.
<4> A dispersion step of dispersing in a solvent at least one of the cellulose fiber produced by the method for producing a cellulose fiber according to <1> and the cellulose fiber according to any one of <2> to <3>. It is a manufacturing method of the fine cellulose fiber dispersion characterized by including.
<5> A fine cellulose fiber dispersion in which cellulose fibers are finely dispersed in a solvent,
The cellulose fiber is a cellulose fiber that can be finely dispersed in a solvent after drying,
After drying the cellulose fiber at 105 ° C. for 3 hours, the cellulose fiber is diluted with water to a concentration of 0.1% by mass to obtain a 40 mL dispersion, and the dispersion is placed in a 50 mL container. After defibrating for 2 minutes at 7,500 rpm using a cylindrical homogenizer, when the fiber is defibrated for 8 minutes with an ultrasonic homogenizer while cooling around the vessel with ice water, the light transmittance at a wavelength of 600 nm of the dispersion is It is a fine cellulose fiber dispersion characterized by having a birefringence of 80% or more.
<6> A drying step of drying at least one of the fine cellulose fiber dispersion produced by the production method according to <4> and the fine cellulose fiber dispersion described in <5>, This is a method for producing fine cellulose fibers.

According to the present invention, the conventional problems can be solved and the object can be achieved, and even if it is once dried, it can be finely dispersed in a solvent in the same manner as when prepared from an undried state. Cellulose fibers that can be reduced in transportation costs and have excellent storage stability, a cellulose fiber production method that can easily produce the cellulose fibers with a low environmental load, and fine cellulose using the cellulose fibers A fiber dispersion and a method for producing the same, and a method for producing fine cellulose fibers using the fine cellulose fiber dispersion can be provided.

FIG. 1 is a graph showing the results of measuring the light transmittance of the dispersions of Examples 1 and 2 and Comparative Example 1. FIG. 2 is a photograph confirming the state of light transmission of the dispersions of Example 1 and Comparative Example 1. FIG. 3 is a photograph observing the birefringence of the dispersions of Example 1 and Comparative Example 1. FIG. 4 is a graph showing the results of measuring the ultraviolet absorption spectrum of Test Example 1. FIG. 5 is a graph showing the results of measuring the light transmittance of the dispersion in Test Example 2-1. FIG. 6 is a graph showing the results of measuring the ultraviolet absorption spectrum of Test Example 2-2.

(Cellulose fiber and production method thereof)
The cellulose fiber of this invention can be suitably manufactured with the manufacturing method of the cellulose fiber of this invention. Hereinafter, the cellulose fiber of this invention is demonstrated with description of the manufacturing method of the cellulose fiber of this invention.

<Method for producing cellulose fiber>
The method for producing a cellulose fiber of the present invention includes at least an oxidation step, a reduction step, and a drying step, and further includes other steps such as a further oxidation step as necessary.

<< Oxidation process >>
The oxidation step is a step of obtaining oxidized cellulose fibers by oxidizing a cellulosic material in a reaction solution containing an N-oxyl compound and a co-oxidant.

-Cellulosic materials-
The cellulose-based raw material is not particularly limited and may be appropriately selected depending on the intended purpose. For example, softwood pulp, hardwood pulp, cotton pulp such as cotton linter or cotton lint, straw pulp, bagasse pulp, etc. Non-wood pulp, bacterial cellulose, cellulose isolated from sea squirt, cellulose isolated from seaweed, and the like. These may be used individually by 1 type and may use 2 or more types together.
The cellulosic material may be subjected to a treatment for increasing the surface area such as beating.

There is no restriction | limiting in particular as the dispersion medium of the said cellulose raw material in the said reaction liquid, According to the objective, it can select suitably, For example, water etc. are mentioned.
There is no restriction | limiting in particular as a density | concentration of the said cellulose raw material in the said reaction liquid, According to the objective, it can select suitably.

-N-oxyl compound-
The N-oxyl compound is not particularly limited and may be appropriately selected depending on the intended purpose. For example, ““ Cellulose ”Vol. 10, 2003, pages 335-341. Shibata and A.I. Examples include the compounds described in “The Catalytic Oxidation of Cellulose Using TEMPO Derivatives: HPSEC and NMR Analysis of Oxidation Products” by Isogai. These may be used individually by 1 type and may use 2 or more types together.
Specific examples of the N-oxyl compound include 2,2,6,6-tetramethylpiperidine-N-oxyl (hereinafter sometimes referred to as “TEMPO”), 4-acetamido TEMPO, 4-carboxy-TEMPO, 4-phosphonooxy-TEMPO and the like can be mentioned.
The content of the N-oxyl compound in the reaction solution is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include a catalyst amount.

-Co-oxidizer-
The co-oxidant is not particularly limited and may be appropriately selected depending on the intended purpose. For example, hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogen acid or a salt thereof, hydrogen peroxide And perorganic acids. These may be used individually by 1 type and may use 2 or more types together.
Specific examples of the co-oxidant include sodium hypochlorite and sodium hypobromite.
There is no restriction | limiting in particular as content of the said co-oxidant in the said reaction liquid, According to the objective, it can select suitably.

-Other ingredients-
The reaction liquid may contain other components other than the above-described cellulose-based material, N-oxyl compound, and co-oxidant.
There is no restriction | limiting in particular as said other component, According to the objective, it can select suitably, For example, a bromide, iodide, or a mixture thereof etc. are mentioned.

--Bromide, iodide, or a mixture thereof--
There is no restriction | limiting in particular as said bromide and iodide, According to the objective, it can select suitably, For example, an alkali metal bromide, an alkali metal iodide, etc. are mentioned. These may be used individually by 1 type and may use 2 or more types together.
There is no restriction | limiting in particular as content of the said bromide, iodide, or these mixtures in the said reaction liquid, According to the objective, it can select suitably.

The conditions such as pH of the reaction solution, reaction temperature, pressure, and reaction time in the oxidation step are not particularly limited and can be appropriately selected depending on the purpose.

-Oxidized cellulose fiber-
The oxidized cellulose fiber obtained by the oxidation step has a carboxyl group content of 0.8 mmol / g to 2.2 mmol / g and an aldehyde group content of 0.8 mmol / g or less.
The amount of carboxyl group and aldehyde group in the oxidized cellulose fiber is determined according to “T. Saito and A. Isogai”, “TEMPO-mediated oxidation of native cellulose. The effect of oxidative conditions in chemistry and chemistry. Biomacromolecules, Vol. 5, pp. 1983 to 1989, 2004 ”, and can be measured by an additional oxidation treatment with sodium chlorite and conductivity titration.

Moreover, by selecting the conditions for the oxidation step, an oxidized cellulose fiber that does not contain an aldehyde group can be obtained without performing a later-described additional oxidation step.
The conditions for the oxidation step not containing the aldehyde group are not particularly limited. For example, “S. Saito, M. Hirota, N. Tamura, S. Kimura, H. Fukuzumi, L. Heux, A. Isogai,“ Individualization. of nano-sized plant cells fibers by direct surface carboxylating using TEMPO catalyst unneutral conditions, Biomacromolecules, Vol. 10, pp. 1992-1996, 2009 ”can be appropriately selected.

<<< Additional oxidation process >>>
A further oxidation step may be included between the oxidation step and a reduction step described later.
The additional oxidation step is a step of further oxidizing the oxidized cellulose fiber obtained in the oxidation step with sodium chlorite.
The conditions for the additional oxidation process are not particularly limited. For example, “T. Saito and A. Isogai”, “TEMPO-mediated oxidation of native cellulose chemistry and the conditions of oxidative conditions for chemistry. ", Biomacromolecules, Vol. 5, pp. 1983 to 1989, 2004 ”can be appropriately selected.
Oxidized cellulose fibers not containing an aldehyde group can be obtained by oxidizing the aldehyde group generated in a small amount at the C6 position to a carboxyl group by the additional oxidation step.

The oxidized cellulose fiber obtained in the oxidation step or the oxidized cellulose fiber obtained in the additional oxidation step may be used in a reduction step described later after suction filtration washing with water.
Since the oxidized cellulose fibers are not dispersed evenly to the nanofiber unit at this stage, they can be washed by a normal water washing-suction filtration washing method.
Specific examples of the washing method include a method of washing and washing with at least one of suction filtration and centrifugation. The number of times of washing may be one time or a plurality of times. The unreacted cooxidant and various byproducts can be removed by the washing.

<< Reduction process >>
The reduction step is a step of reducing the oxidized cellulose fibers in a reaction solution containing a reducing agent to obtain reduced oxidized cellulose fibers.
In the oxidation step, a ketone group is generated at the C2 position and the C3 position in the oxidized cellulose fiber as a side reaction. In addition, when weakly alkaline oxidation reaction conditions are used, a small amount of an aldehyde group is generated at the C6 position in addition to the above-described ketone group. In addition, when the oxidation step is performed using TEMPO, NaClO, and NaClO ₂ that are weakly acidic to neutral, there is no aldehyde at the C6 position of the oxidized cellulose fiber. Further, when the oxidation step is performed using TEMPO, NaBr, and NaClO with weak alkalinity, and then the additional oxidation step is performed, the aldehyde group at the C6 position of the oxidized cellulose fiber does not exist.
In the reduction step, at least a part of the ketone group and / or aldehyde group is converted to an alcoholic hydroxyl group. That is, in the reduced oxidized cellulose fiber obtained in the reduction step, the amount of the ketone group or the amount of both the ketone group and the aldehyde group is less than the amount in the oxidized cellulose fiber.

-Oxidized cellulose fiber-
The oxidized cellulose fiber is an oxidized cellulose fiber obtained by the oxidation process described above.
There is no restriction | limiting in particular as content of the said oxidized cellulose fiber in the said reaction liquid, According to the objective, it can select suitably.

-Reducing agent-
The reducing agent is not particularly limited and may be appropriately selected depending on the intended purpose. For example, sodium borohydride, thiourea, hydrosulfite, sodium bisulfite, sodium cyanoborohydride, lithium borohydride Etc. These may be used individually by 1 type and may use 2 or more types together.
Among the reducing agents, sodium borohydride is preferable because of excellent selective reactivity.

The solvent in the reaction solution is preferably water.
There is no restriction | limiting in particular as content of the said reducing agent in the said reaction liquid, Although it can select suitably according to the objective, 0.001g or more is preferable with respect to the said dry oxidized cellulose fiber, and 0 0.01 g or more is more preferable.

The said reaction liquid may contain other components other than the oxidized cellulose fiber mentioned above and a reducing agent.
The other components are not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately selected according to the purpose.

-PH-
The pH of the reaction solution is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 7 to 11, more preferably 9 to 10, and particularly preferably 10. When the pH is in a more preferable range, the amount of ketone groups or the amount of ketone groups and aldehyde groups in the reduced oxidized cellulose fiber can be reduced, and when the pH is in a particularly preferable range, Even when the amount of reducing agent used is reduced, it is advantageous in that the amount of ketone groups or the amount of ketone groups and aldehyde groups in the reduced oxidized cellulose fiber can be further reduced.

There is no restriction | limiting in particular as reaction temperature in the said reduction | restoration process, According to the objective, it can select suitably, For example, it can be 4 to 40 degreeC.
There is no restriction | limiting in particular as a pressure in the said reduction | restoration process, According to the objective, it can select suitably, For example, it can be set as a normal pressure.
There is no restriction | limiting in particular as reaction time in the said reduction | restoration process, Although it can select suitably according to the objective, 1 hour or more is preferable and 5 hours or more are more preferable.
The reduction step is preferably performed while stirring the reaction solution.

The reduced-type oxidized cellulose fiber obtained in the reduction step is preferably used in a drying step described later after washing.
The reduced oxidized cellulose fibers are not dispersed evenly to the nanofiber unit at this stage, and can be washed by a normal washing method.
Specific examples of the cleaning method include the same methods as those described in the above oxidation step.

<< Drying process >>
The drying step is a step of drying the reduced oxidized cellulose fiber.

There is no restriction | limiting in particular as said drying method, According to the objective, it can select suitably, For example, the drying method using an oven dryer, the freeze-drying method, the spray-drying method etc. are mentioned.
The drying conditions are not particularly limited and may be appropriately selected depending on the purpose.

<< Other processes >>
The other steps are not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately selected according to the purpose.

<Cellulose fiber>
The cellulose fiber of the present invention can be suitably produced by the above-described method for producing a cellulose fiber of the present invention, and can be finely dispersed in a solvent even after drying.
There is no restriction | limiting in particular as a drying degree of the said cellulose fiber, According to the objective, it can select suitably.

-Fine dispersion-
The cellulose fibers can be finely dispersed in water at a solid content of 0.01% by mass to 5% by mass after drying at 105 ° C. for 3 hours.
The drying conditions at 105 ° C. for 3 hours are generally the absolutely dry conditions for cellulose fibers.

Whether or not the cellulose fiber can be finely dispersed in a solvent can be confirmed, for example, as follows.

--- Light transmission ---
The cellulose fiber (reduced oxidized cellulose fiber obtained in the drying step) is dried at 105 ° C. for 3 hours. After the drying, the cellulose fiber is diluted with water to a concentration of 0.1% by mass to obtain a 40 mL dispersion. The dispersion was placed in a 50 mL centrifuge tube (polypropylene; manufactured by Corning) and used as it was by using a double-cylindrical homogenizer (blade diameter 1.5 cm, Microtech Nichion NS-56). Defibration treatment is performed at 500 rpm for 2 minutes. Next, after the defibrating treatment with the double cylinder type homogenizer, the surroundings of the container are immediately cooled with ice water as they are, and the ultrasonic homogenizer (US-300T, manufactured by Nippon Seiki Co., Ltd., probe tip 7 mm, output 300 W, 19.5 kHz) is used for 8 minutes. Perform defibrating treatment.
In the treatment with the ultrasonic homogenizer, in order to avoid the temperature rise of the dispersion due to the ultrasonic treatment, a cycle of ultrasonic treatment for 2 minutes and standing and cooling for 1 minute is repeated, and the total ultrasonic treatment time is reached. For 8 minutes.
The whole dispersion having a cellulose fiber concentration of 0.1% by mass obtained as described above (a dispersion without removing any defibrated material. There is no defibrated material after complete nano-dispersion. Light transmittance at a wavelength of 600 nm (hereinafter sometimes referred to as “transmittance”) is measured, and if the light transmittance is 80% or more, it is finely dispersed (nanodispersed). I can judge. When the light transmittance does not reach 80%, it can be determined that the fiber contains undefibrated components that are not finely dispersed.

--- Birefringence--
Whether or not the cellulose fibers can be finely dispersed in a solvent can also be confirmed by confirming whether or not the cellulose fiber dispersion exhibits birefringence.
As a method for confirming the birefringence, for example, the dispersion prepared by the measurement of the “light transmittance” (if there is undefibrated residue, removed by centrifugation) is placed between orthogonal polarizing plates. It can be confirmed by observing the birefringence.

-Amount of ketone group, amount of aldehyde group-
The cellulose fiber of the present invention is a reduced oxidation in which the amount of the ketone group or the amount of the ketone group and the aldehyde group is reduced by the reduction step compared to the amount in the oxidized cellulose fiber after the oxidation step or the additional oxidation step. Cellulose fiber.
The reduced oxidized cellulose fiber can be refined in water (nanodispersion) even after the drying step.
In the reduced oxidized cellulose fiber, the method for confirming that the amount of the ketone group or the amount of the ketone group and the aldehyde group is reduced is not particularly limited and can be appropriately selected according to the purpose. For example, it can be confirmed by measuring an ultraviolet absorption spectrum according to the following procedure.

--- Preparation of fine dispersion-
The cellulose fiber is dried at 105 ° C. for 3 hours. After the drying, the cellulose fiber is diluted with water to a concentration of 0.1% by mass to obtain a 40 mL dispersion. The dispersion was placed in a 50 mL centrifuge tube (polypropylene; manufactured by Corning) and used as it was by using a double-cylindrical homogenizer (blade diameter 1.5 cm, Microtech Nichion NS-56). Defibration treatment is performed at 500 rpm for 2 minutes. Next, after the defibrating treatment with the double cylinder type homogenizer, the surroundings of the container are immediately cooled with ice water as they are, and the ultrasonic homogenizer (US-300T, manufactured by Nippon Seiki Co., Ltd., probe tip 7 mm, output 300 W, 19.5 kHz) is used for 8 minutes. A defibrating treatment is performed to prepare a dispersion having a cellulose fiber concentration of 0.1% by mass.
In the treatment with the ultrasonic homogenizer, in order to avoid the temperature rise of the dispersion due to the ultrasonic treatment, a cycle of ultrasonic treatment for 2 minutes and standing and cooling for 1 minute is repeated, and the total ultrasonic treatment time is reached. For 8 minutes.
The concentration of the cellulose fiber in the dispersion can be appropriately selected within the range of 0.05% by mass to 0.5% by mass.

Subsequently, in order to remove the undisentangled cellulose fibers in the dispersion, the undissolved cellulose fibers are removed by centrifuging with a centrifuge at 12,000 G for 10 minutes while leaving the container. A supernatant containing no cellulose fibers is obtained. Here, when the absorbance at a wavelength of 600 nm of the dispersion subjected to the defibration treatment in water is less than 80%, and the weight ratio of the undefibrated portion removed by centrifuging and removing the dispersion is 10% or more. The cellulose fiber contained in the dispersion is judged as “cannot be nanodispersed in water”.

--- Preparation of fine cellulose fiber film--
The supernatant is poured into a petri dish, dried in a drier, and peeled from the petri dish to obtain a fine cellulose fiber film (hereinafter sometimes referred to as “cast film”).
The injection amount of the supernatant is adjusted so that the thickness of the cast film is 5 μm to 50 μm. The cast film has a density of 1 g / cm ³ to 1.6 g / cm ³ . The film thickness of the cast film may be adjusted by adjusting the size of the petri dish.
There is no restriction | limiting in particular as a material of the said petri dish, According to the objective, it can select suitably, For example, a polystyrene etc. are mentioned.
The temperature of the dryer is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably room temperature to 50 ° C., more preferably 40 ° C.
The drying period is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 3 days to 6 days, and more preferably 5 days.

--Measurement of UV absorption spectrum--
The cast film is heated at 105 ° C. for 3 hours and then cooled at room temperature to obtain a dry cast film.
The ultraviolet absorption spectrum (range of 190 nm to 400 nm) of the dried cast film is measured.

--- Confirmation that the amount of ketone groups or the amount of ketone groups and aldehyde groups has been reduced ---
The amount of aldehyde group and ketone group in the original cellulose fiber can be measured from the absorbance value of the ultraviolet absorption spectrum.
Specifically, when the C2-position and C3-position ketone groups are present in the original cellulose fiber, the absorbance at 290 nm of the ultraviolet absorption spectrum increases. Further, when an aldehyde group is present in the original cellulose fiber, the absorbance at 260 nm of the ultraviolet absorption spectrum increases. On the other hand, when the amount of sodium borohydride added to the oxidized cellulose fiber is sufficient in the reduction step (for example, when 0.01 g of sodium borohydride is added to 1 g of oxidized cellulose fiber) There are no ketone groups or aldehyde groups in the cellulose fiber, and no peak is observed at 290 nm and 260 nm when the ultraviolet absorption spectrum is measured.
The ultraviolet absorbance of the cast film affects the thickness of the film (the greater the thickness of the film, the greater the absorbance and the smaller the thickness). Therefore, by dividing the absorbance by the thickness of the film, it is possible to evaluate and compare with the normalized absorbance (standardized conditions). Specifically, the absorbance at 290 nm and 260 nm is corrected to the absorbance per 1 μm thickness of the cast film, and evaluated and compared.
However, when hexeneuronic acid groups are present in the dry cast film, absorption is observed at 235 nm. In this case, since the absorbance at 260 nm is overestimated, the value obtained by correcting the absorbance at 260 nm to the absorbance per 1 μm thickness of the dry cast film is corrected by multiplying by 0.7.
The cellulose fiber of the present invention is a value obtained by correcting the absorbance of the dry cast film at wavelengths of 290 nm and 260 nm to the absorbance per 1 μm thickness of the dry cast film (however, in the measurement of the ultraviolet absorption spectrum, it is derived from hexene uronic acid groups). When the absorption at 235 nm is observed, the value obtained by correcting the absorbance at 260 nm to the absorbance per 1 μm thickness of the dry cast film is a value obtained by multiplying the corrected value by 0.7). , Both are preferably 0.020 or less.

In addition, the amount of aldehyde groups and ketone groups in cellulose fibers by the above method can be applied to undried cellulose fibers.
Since the aldehyde group amount and the ketone group amount in the undried cellulose fiber and the dried cellulose fiber can be measured by the above method, whether or not the reduction step has been performed on the unknown cellulose fiber sample. Can be determined.

Even when the cellulose fiber of the present invention is once dried, it can be finely dispersed in a solvent in the same manner as when prepared from an undried state, so that the cost for transportation can be reduced. Excellent storage stability.

(Fine cellulose fiber dispersion and production method thereof)
The fine cellulose fiber dispersion of the present invention can be suitably produced by the method for producing a fine cellulose fiber dispersion of the present invention. Hereinafter, the fine cellulose fiber dispersion of the present invention will be described together with the description of the method for producing the fine cellulose fiber dispersion of the present invention.

<Method for producing fine cellulose fiber dispersion>
The method for producing a fine cellulose fiber dispersion of the present invention includes at least a dispersion step, and further includes other steps as necessary.

<< dispersion process >>
The said dispersion | distribution process is a process of disperse | distributing the cellulose fiber of this invention mentioned above in the solvent. The cellulose fiber can be finely dispersed by the dispersing step.

-solvent-
The solvent is not particularly limited and may be appropriately selected depending on the intended purpose. Water, alcohols, ethers, ketones, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide Etc. These may be used individually by 1 type and may use 2 or more types together.
Specific examples of the alcohols include methanol, ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, methyl cellosolve, ethyl cellosolve, ethylene glycol, glycerin and the like.
Specific examples of the ethers include ethylene glycol dimethyl ether, 1,4-dioxane, tetrahydrofuran and the like.
Specific examples of the ketones include acetone and methyl ethyl ketone.
Among the solvents, water is preferable.

-dispersion-
The dispersion means used in the dispersion step (hereinafter also referred to as “defibration means”) is not particularly limited and may be appropriately selected depending on the intended purpose. For example, a screw mixer, paddle mixer, disperser Type mixer, turbine type mixer, homomixer under high speed rotation, high pressure homogenizer, super high pressure homogenizer, double cylinder type homogenizer, ultrasonic homogenizer, water flow collision type disperser, beater, disk type refiner, conical type refiner, double Examples thereof include a disk type refiner, a grinder, and a twin-screw kneader.

The conditions for the dispersion step are not particularly limited and may be appropriately selected depending on the purpose. For example, the above-mentioned “light transmittance” column and “fine amount of ketone group, amount of aldehyde group” “fine” Examples of the conditions for the preparation of the dispersion described in the column “Preparation of dispersion”.
By the dispersion step, the above-described cellulose fiber of the present invention is finely dispersed, and a fine cellulose fiber dispersion in which the fine cellulose fiber is dispersed is obtained.
The fine cellulose fibers are cellulose single microfibrils having a width of about 2 nm to 5 nm and a length of about 0.2 μm to 5 μm.

(Fine cellulose fiber and method for producing fine cellulose fiber)
The fine cellulose fiber of this invention can be suitably manufactured with the manufacturing method of the fine cellulose fiber of this invention. Hereinafter, the fine cellulose fiber of this invention is demonstrated with description of the manufacturing method of the fine cellulose fiber of this invention.

<Method for producing fine cellulose fiber>
The manufacturing method of the fine cellulose fiber of this invention includes a drying process at least, and also includes another process as needed.

<< Drying process >>
The drying step is a step of drying the fine cellulose fiber dispersion of the present invention described above.
There is no restriction | limiting in particular as said drying method, It can carry out similarly to the drying process in the manufacturing method of the cellulose fiber of this invention mentioned above.
Fine cellulose fibers can be obtained by the drying step.

The fine cellulose fiber can be suitably used in various fields such as an oxygen-preventing membrane, a general-purpose plastic reinforcing material, a medical material, a cell culture substrate, a catalyst carrier, an adsorbent, and a separating material.

(Fine cellulose fiber molded body and production method thereof)
The said fine cellulose fiber molded object can be suitably manufactured with the manufacturing method of the following fine cellulose fiber molded objects. Hereinafter, the said fine cellulose fiber molded object is demonstrated with description of the manufacturing method of a fine cellulose fiber molded object.

<Manufacturing method of fine cellulose fiber molding>
The manufacturing method of the said fine cellulose fiber molded object includes at least the process of removing a liquid component, hold | maintaining the fine cellulose fiber dispersion of this invention mentioned above in the predetermined shape, and also includes another process as needed.

The method for removing the liquid component while holding the fine cellulose fiber dispersion in a predetermined shape is not particularly limited and may be appropriately selected depending on the purpose. For example, the fine cellulose fiber dispersion may be selected on a substrate such as a glass plate. Examples include a method of forming a film by removing the liquid component of the dispersion by a drying method such as natural drying, air blowing drying, or vacuum drying after casting the cellulose fiber dispersion.
A fine cellulose fiber molded body can be obtained by peeling the film from the substrate.

Moreover, it is good also as a fine cellulose fiber molded object by forming a fine cellulose fiber layer on the molded object using the said fine cellulose fiber dispersion.
There is no restriction | limiting in particular as said molded object, According to the objective, it can select suitably, For example, foil-like articles, such as a film, a sheet | seat, a woven fabric, and a nonwoven fabric which have desired shape and magnitude | size, desired shape, and A three-dimensional container such as a box or a bottle can be used.
There is no restriction | limiting in particular as a material of the said molded object, According to the objective, it can select suitably, For example, paper, paperboard, a plastics, a metal, these composites etc. are mentioned.
The structure of the molded product may be a single layer or multiple layers.

There is no restriction | limiting in particular as a method to provide the said fine cellulose fiber dispersion on the said molded object, According to the objective, it can select suitably, For example, the apply | coating method, the spraying method, the immersion method etc. are mentioned.
Further, a fine cellulose fiber molded body formed in a film shape may be bonded to the surface of the molded product. There is no restriction | limiting in particular as the said bonding method, According to the objective, it can select suitably, For example, the method of using an adhesive agent, the heat sealing | fusion method, etc. are mentioned.

(Fine cellulose fiber composite and its production method)
The said fine cellulose fiber composite body can be suitably manufactured with the manufacturing method of the following fine cellulose fiber composite bodies. Hereinafter, the said fine cellulose fiber composite is demonstrated with description of the manufacturing method of a fine cellulose fiber composite.

<Method for producing fine cellulose fiber composite>
The method for producing the fine cellulose fiber composite includes at least a step of preparing a dispersion liquid obtained by mixing the above-described fine cellulose fiber dispersion of the present invention and a liquid material containing the composite material. And other steps.

The material of the composite is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include synthetic polymers such as polyvinyl alcohol, nylon (registered trademark), polypropylene, polyethylene terephthalate, and polyester. .
The synthetic polymer can be dissolved in an organic solvent and spun (solution spinning) or shaped into a film.
Therefore, by using a dispersion obtained by mixing the fine cellulose fiber dispersion and a liquid material containing the synthetic polymer, a fibrous molded article or a film-like molded article that is the fine cellulose fiber composite is obtained. be able to.
Also, a monomer and the fine cellulose fiber dispersion are mixed in an organic solvent, and the monomer is polymerized to synthesize a polymer, thereby forming a composite of the fine cellulose fiber and the synthetic polymer. You can also.

Hereinafter, the present invention will be specifically described with reference to examples and the like, but the present invention is not limited to these examples and the like.

Example 1
<Oxidation process>
After dispersing softwood bleached kraft pulp (corresponding to 4 g in dry mass), 62.4 mg of TEMPO, and 0.4 g of sodium bromide in 400 mL of distilled water, 13 g of aqueous sodium hypochlorite solution was added to 1 g of The reaction was started by adding sodium hypochlorite to the pulp in an amount of 5 mmol. During the reaction, a 0.5 M aqueous sodium hydroxide solution was added dropwise to keep the pH at 10, and the reaction was carried out with stirring at room temperature (20 ° C. to 25 ° C.). When the change in pH is no longer observed, the reaction is considered to be complete, the reaction product is filtered through a glass filter, washed with a sufficient amount of water and filtered five times, and the solid content is 9.3% by mass. Some oxidized cellulose fibers were obtained (yield> 90%).
The amount of carboxyl groups of the oxidized cellulose fiber was 1.43 mmol / g, and the amount of aldehyde groups was 0.04 mmol / g. The amount of carboxyl group and aldehyde group per gram of the oxidized cellulose is determined according to “T. Saito and A. Isogai”, “TEMPO-mediated oxidation of native cell oxidization and qualitative chemistry and chemistry”. Biomacromolecules, Vol. 5, pp. 1983 to 1989, 2004 ”, and was measured by an additional oxidation treatment with sodium chlorite and conductivity titration.

<Reduction process>
To 1 g of the oxidized cellulose fiber, 100 mL of distilled water and 1/64 g of sodium borohydride were added, and the pH was adjusted to 10 with a 0.5 M sodium hydroxide aqueous solution to start the reaction. The reaction was carried out for 24 hours with stirring at room temperature (20 ° C. to 25 ° C.). After filtering the reaction product with a glass filter, washing with a sufficient amount of water and filtration were repeated 5 times to obtain an undried (hydrated) reduced oxidized cellulose fiber having a solid content of 4.4% by mass. (Yield 80%).

<Drying process>
The reduced oxidized cellulose fiber obtained in the reduction step was dried at 105 ° C. for 3 hours or more using an oven to obtain reduced oxidized cellulose fiber having a solid content of 100% by mass.

<Dispersing process>
Water was added to the reduced oxidized cellulose fiber obtained in the drying step, and 40 mL of a dispersion diluted to have a cellulose concentration of 0.1% by mass was centrifuged in a 50 mL container (made of polypropylene; manufactured by Corning). Then, using a double cylindrical homogenizer (blade diameter 1.5 cm, NS-56 manufactured by Microtech Nichion Co., Ltd.) for 2 minutes at 7,500 rpm. After the defibrating process with the double cylindrical homogenizer, it is defibrated with an ultrasonic homogenizer (Nippon Seiki US-300T, probe tip 7 mm, output 300 W, 19.5 kHz) for 8 minutes while immediately cooling the surroundings with ice water. Processed. In the sonication, in order to avoid the temperature rise of the dispersion, a cycle of sonicating for 2 minutes and allowing to cool for 1 minute is repeated so that the total sonication time becomes 8 minutes. went. With the above treatment, a dispersion having a cellulose concentration of 0.1% by mass was obtained.

<Light transmission>
The light transmittance of the dispersion liquid (a dispersion liquid that remains unremoved even if there is undefibrated material, which may be completely nanodispersed and may have no undefibrated material) is measured by an ultraviolet-visible near infrared spectrophotometer The results of measurement using V-670 manufactured by JASCO Corporation are shown in FIG. 1 (“NaBH ₄ addition amount: 1/64 of the weight of pulp” in FIG. 1). The light transmittance of the dispersion at a wavelength of 600 nm was 90.9%.
The state of light transmission of the dispersion is shown in FIG.

<Birefringence>
In the dispersion liquid, when there was an undefibrated residue, it was removed by centrifugation. This centrifuged dispersion was placed between orthogonal polarizing plates, and it was confirmed whether birefringence was observed. The results are shown in FIG.

(Comparative Example 1)
In Example 1, except that the reduction step was not performed, a dispersion having a cellulose concentration of 0.1% by mass (a dispersion without being removed even if undefibrated material was present) in the same manner as in Example 1. ) The results of measuring the dispersion in the same manner as in Example 1 are shown in FIG. 1 (“untreated” in FIG. 1). The light transmittance of the dispersion at a wavelength of 600 nm was 39.4%.
The state of light transmission of the dispersion is shown in FIG.

Whether or not birefringence was observed was confirmed in the same manner as in Example 1 for the dispersion of Comparative Example 1. The results are shown in FIG.

From the results of Example 1 and Comparative Example 1, it was not possible to finely disperse the cellulose fibers after the drying process in the dispersion liquid of Comparative Example 1 in which the reduction process of the present invention was not performed. On the other hand, since the dispersion of Example 1 has a light transmittance of 600% or more at a wavelength of 600 nm and birefringence was observed, the reduction step of the present invention is performed, and then the drying step is performed. Even so, it has been shown that cellulose fibers can be finely dispersed.

(Example 2)
In the reduction step of Example 1, the cellulose concentration was 0.1 mass in the same manner as in Example 1 except that the amount of sodium borohydride used was 1/32 g with respect to 1 g of the oxidized cellulose fiber. % Dispersion (dispersion that remains unremoved even if undefibrated material is present). The results obtained by measuring the dispersion in the same manner as in Example 1 are shown in FIG. 1 (“NaBH ₄ addition amount: 1/32 of the weight of the pulp” in FIG. 1). The light transmittance of the dispersion at a wavelength of 600 nm was 91.5%.
Further, when it was confirmed whether or not birefringence was observed in the same manner as in Example 1, the birefringence was confirmed.
Therefore, also in Example 2, it was shown that it is possible to finely disperse the cellulose fibers after the drying process.

(Test Example 1: Ketone group amount and aldehyde group amount)
For the dispersions of Examples 1 and 2 and Comparative Example 1, undefibrated portions were removed by centrifugation, the supernatant dispersion was poured into a petri dish, dried in a dryer at 40 ° C. for 5 days, From the film, a cast film of cellulose nanofibers was obtained (film thickness: 5 μm to 10 μm). The ultraviolet absorption spectrum (range of 190 nm to 400 nm) of each cast film was measured. The results are shown in Table 1 and FIG. In FIG. 4, “NaBH ₄ addition amount: 1/64 of the weight of the pulp” uses the dispersion liquid of Example 1, and “NaBH ₄ addition amount: 1/32 of the weight of the pulp” uses the dispersion liquid of Example 2. Used, “untreated” indicates the ultraviolet absorption spectrum of the cast film obtained using the dispersion of Comparative Example 1.
In addition, as a result of measuring the ultraviolet absorption spectrum of each cast film of Examples 1 and 2 and Comparative Example 1, absorption at 235 nm derived from hexeneuronic acid groups was observed, so the absorbance per 1 μm thickness of the cast film was The value obtained by correcting and further multiplying the absorbance by 0.7 was defined as a “value corrected to the absorbance per 1 μm thickness of the cast film”.

The absorbance at 260 nm corresponds to the amount of aldehyde groups, and the absorbance at 290 nm corresponds to the amount of ketone groups.
As shown in Table 1, in Comparative Example 1 in which the reduction process was not performed, the absorbance at 260 nm and the absorbance at 290 nm were 0.050 or more, whereas Example 1 in which the reduction process was performed and 2, the absorbance at 260 nm and the absorbance at 290 nm were both 0.020 or less.
Therefore, it was shown that in order to finely disperse the cellulose fibers after the drying step, the absorbance at 260 nm and the absorbance at 290 nm must both be 0.020 or less.

Example 3
Undried TEMPO oxidized cellulose (manufactured by Nippon Paper Industries Co., Ltd., carboxyl group amount; 1.45 mmol / g, aldehyde group amount; 0.05 mmol / g, solid content rate: 15.95%) was measured for an absolute dry weight of 2 g. And dispersed in 200 mL of distilled water. The pH of this dispersion was adjusted to 10 with a 0.05 M aqueous sodium hydroxide solution, and 0.5 g of sodium borohydride was added to initiate the reaction. The reaction was carried out for 24 hours with stirring at room temperature. After the reaction product was filtered through a glass filter, washing with a sufficient amount of water and filtration were repeated four times to obtain reduced oxidized cellulose fibers having a solid content of 7.7% by mass (yield 88%). .
The reduced oxidized cellulose fibers were dried at 105 ° C. for 3 hours or more using an oven to obtain reduced oxidized cellulose fibers having a solid content of 100% by mass.

(Comparative Example 2)
Undried TEMPO oxidized cellulose (manufactured by Nippon Paper Industries Co., Ltd., carboxyl group amount; 1.45 mmol / g, aldehyde group amount; 0.05 mmol / g, solid content rate: 15.95%) was measured for an absolute dry weight of 2 g. And dispersed in 150 mL of distilled water. 2N sulfuric acid was added to this dispersion to adjust the pH to 7.0. Thereafter, the reaction solution was filtered using a glass filter. Cellulose fibers obtained by this filtration were added to a water-containing solvent (acetone: water = 50: 50 [volume ratio]) as a washing liquid, and the mixture was stirred and dispersed uniformly while maintaining pH 7.0. This was again filtered using a glass filter. This operation was further repeated 4 times to purify the cellulose fiber. After purification, this sample was allowed to stand at room temperature for 2 days and dried to obtain a dried product. The dried product had a loss on drying of 16%.

(Comparative Example 3)
Undried TEMPO oxidized cellulose (manufactured by Nippon Paper Industries Co., Ltd., carboxyl group amount; 1.45 mmol / g, aldehyde group amount; 0.05 mmol / g, solid content rate; 15.95%) was prepared.

(Test Example 2-1: Light transmission and birefringence)
For each of the dried cellulose obtained in Example 3 and Comparative Example 2, 40 mL of a dispersion diluted with water so that the cellulose concentration was 0.1% by mass was centrifuged in a 50 mL container (made of polypropylene; Corning Then, the fiber was defibrated for 2 minutes at 7,500 rpm using a double cylinder type homogenizer (blade diameter 1.5 cm, NS-56 manufactured by Microtech Nichion Co., Ltd.). After the defibrating process with the double cylindrical homogenizer, it is defibrated with an ultrasonic homogenizer (Nippon Seiki US-300T, probe tip 7 mm, output 300 W, 19.5 kHz) for 8 minutes while immediately cooling the surroundings with ice water. Processed. In the sonication, in order to avoid the temperature rise of the dispersion, a cycle of sonicating for 2 minutes and allowing to cool for 1 minute is repeated so that the total sonication time becomes 8 minutes. went. With the above treatment, a dispersion liquid (including undefibrated parts) having a cellulose concentration of 0.1% by mass was obtained.

<Light transmission>
FIG. 5 shows the results of measuring the light transmittance of each dispersion in the same manner as in Example 1. The light transmittance at a wavelength of 600 nm of each of the dispersions was 91.1% for the dispersion of Example 3, whereas it was 68.7% for the dispersion of Comparative Example 2.

<Birefringence>
Each of the dispersion liquids was checked for birefringence in the same manner as in Example 1. As a result, birefringence was confirmed in the dispersion liquid of Example 3. On the other hand, in the dispersion liquid of Comparative Example 2, although birefringence was confirmed in the supernatant, the weight ratio of the undefibrated portion removed by centrifugation was 31%, and nanodispersion in water was not possible.

(Test Example 2-2: Ketone group amount and aldehyde group amount)
(1) Undried TEMPO oxidized cellulose prepared in Comparative Example 3, (2) In Comparative Example 2, undried TEMPO oxidized cellulose (solid content: 18.58%) after purification and before drying, and (3) For each of the reduced oxidized cellulose fibers before drying in Example 3, water was added, and 40 mL of a dispersion diluted with water so that the cellulose concentration was 0.1% by mass was centrifuged in a 50 mL container. Put in a tube (made of polypropylene; made by Corning) and use a double cylindrical homogenizer (blade diameter 1.5 cm, NS-56 made by Microtech Nichion Co., Ltd.) for 2 minutes at 7,500 rpm. It was. After the defibrating process with the double cylindrical homogenizer, it is defibrated with an ultrasonic homogenizer (Nippon Seiki US-300T, probe tip 7 mm, output 300 W, 19.5 kHz) for 8 minutes while immediately cooling the surroundings with ice water. Processed. In the sonication, in order to avoid the temperature rise of the dispersion, a cycle of sonicating for 2 minutes and allowing to cool for 1 minute is repeated so that the total sonication time becomes 8 minutes. went. With the above treatment, a dispersion liquid (including undefibrated parts) having a cellulose concentration of 0.1% by mass was obtained.

About each said dispersion liquid, an undisentangled part is removed by centrifugation, the dispersion liquid of supernatant is poured into a petri dish, dried for 5 days in a dryer at 40 ° C., and peeled from the petri dish to thereby remove the cellulose nanofiber film. Obtained (film thickness: 5 to 10 μm). The obtained film was heat-treated with a dryer at 105 ° C. for 3 hours. Thereafter, an ultraviolet absorption spectrum (range of 190 nm to 400 nm) of the heat-treated film was measured. The results are shown in Table 2 and FIG.

From the results of Test Examples 2-1 and 2-2, in Comparative Examples 2 and 3 in which the reduction step was not performed, the absorbance at 260 nm and the absorbance at 290 nm were 0.044 or more, whereas In Example 3 where the process was performed, the absorbance at 260 nm and the absorbance at 290 nm were both 0.020 or less.
Therefore, in order to finely disperse the cellulose fiber after performing the drying process to such an extent that the light transmittance at the wavelength of 600 nm is 80% or more, the reduction process must be performed, and the method of Comparative Example 2 Then, it was shown that cellulose fibers cannot be sufficiently finely dispersed.

It is known that sodium borohydride, which is a reducing agent used in the reduction step, reduces aldehydes and ketones to the corresponding alcohols. Until now, after drying the oxidized cellulose fiber after the oxidation step and the dispersion of fine cellulose fiber obtained by defibrating the oxidized cellulose fiber, it is impossible to finely disperse it on the surface of the cellulose fiber. It has been thought to be due to hydrogen bonds formed between hydroxyl groups. However, according to the present invention, the fine dispersion after drying was inhibited not by the hydrogen bond but by the C2 position, C3 position ketone group and / or C6 position aldehyde group by-produced by the oxidation step. It was quantitatively shown to be due to the formation of a hemiacetal bond with the hydroxyl group.

Examples of the aspect of the present invention include the following.
<1> An oxidation step in which an oxidized cellulose fiber is obtained by oxidizing a cellulosic raw material in a reaction solution containing an N-oxyl compound and a co-oxidant;
A reduction step of reducing the oxidized cellulose fibers in a reaction solution containing a reducing agent to obtain reduced oxidized cellulose fibers;
A drying step of drying the reduced oxidized cellulose fiber,
The cellulose fiber obtained by drying the reduced oxidized cellulose fiber can be finely dispersed in a solvent.
<2> The method for producing a cellulose fiber according to <1>, further including a further oxidation step of further oxidizing the oxidized cellulose fiber obtained in the oxidation step with sodium chlorite between the oxidation step and the reduction step. .
<3> The method for producing a cellulose fiber according to any one of <1> to <2>, wherein the pH of the reaction solution in the reduction step is 9 to 10.
<4> A cellulose fiber produced by the production method according to any one of <1> to <3> and finely dispersible in a solvent.
<5> Cellulose fibers that can be finely dispersed in a solvent after drying,
After drying the cellulose fiber at 105 ° C. for 3 hours, the cellulose fiber is diluted with water to a concentration of 0.1% by mass to obtain a 40 mL dispersion, and the dispersion is placed in a 50 mL container. After defibrating for 2 minutes at 7,500 rpm using a cylindrical homogenizer, when the fiber is defibrated for 8 minutes with an ultrasonic homogenizer while cooling around the vessel with ice water, the light transmittance at a wavelength of 600 nm of the dispersion is It is a cellulose fiber characterized by having a birefringence of 80% or more.
<6> After drying the cellulose fiber at 105 ° C. for 3 hours, the cellulose fiber is diluted with water to a concentration of 0.1% by mass to obtain a 40 mL dispersion, and the dispersion is placed in a 50 mL container. After defibrating for 2 minutes at 7,500 rpm using a double cylindrical homogenizer, defibrating for 8 minutes with an ultrasonic homogenizer while cooling around the vessel with ice water, and then undefibrated cellulose fibers in the dispersion A cast film is prepared using the dispersion obtained by removing, and the cast film is dried at 105 ° C. for 3 hours to obtain a dry cast film. When the ultraviolet absorption spectrum of the dry cast film is measured, a wavelength of 290 nm and A value obtained by correcting the absorbance at 260 nm to the absorbance per 1 μm thickness of the dry cast film (however, the ultraviolet absorption In the measurement of the spectrum, when absorption at 235 nm derived from a hexeneuronic acid group was observed, the value obtained by correcting the absorbance at 260 nm to the absorbance per 1 μm thickness of the dry cast film was 0 to the corrected value. Is a cellulose fiber according to any one of <4> to <5>, wherein all are 0.020 or less.
<7> At least one of the cellulose fiber produced by the method for producing a cellulose fiber according to any one of <1> to <3> and the cellulose fiber according to any one of <4> to <6>. It is a manufacturing method of the fine cellulose fiber dispersion characterized by including the dispersion | distribution process which disperse | distributes to a solvent.
<8> A fine cellulose fiber dispersion produced by the production method according to <7>.
<9> A fine cellulose fiber dispersion in which cellulose fibers are finely dispersed in a solvent,
The cellulose fiber is a cellulose fiber that can be finely dispersed in a solvent after drying,
After drying the cellulose fiber at 105 ° C. for 3 hours, the cellulose fiber is diluted with water to a concentration of 0.1% by mass to obtain a 40 mL dispersion, and the dispersion is placed in a 50 mL container. After defibrating for 2 minutes at 7,500 rpm using a cylindrical homogenizer, when the fiber is defibrated for 8 minutes with an ultrasonic homogenizer while cooling around the vessel with ice water, the light transmittance at a wavelength of 600 nm of the dispersion is It is a fine cellulose fiber dispersion characterized by having a birefringence of 80% or more.
<10> After drying the cellulose fiber at 105 ° C. for 3 hours, the cellulose fiber is diluted with water to a concentration of 0.1% by mass to form a 40 mL dispersion, and the dispersion is placed in a 50 mL container. After defibrating for 2 minutes at 7,500 rpm using a double cylindrical homogenizer, defibrating for 8 minutes with an ultrasonic homogenizer while cooling around the vessel with ice water, and then undefibrated cellulose fibers in the dispersion A cast film is prepared using the dispersion obtained by removing, and the cast film is dried at 105 ° C. for 3 hours to obtain a dry cast film. When the ultraviolet absorption spectrum of the dry cast film is measured, a wavelength of 290 nm and A value obtained by correcting the absorbance at 260 nm to the absorbance per 1 μm thickness of the dry cast film (however, the ultraviolet absorption In the measurement of the spectrum, when absorption at 235 nm derived from hexeneuronic acid groups was observed, the value obtained by correcting the absorbance at 260 nm to the absorbance per 1 μm thickness of the dry cast film was 0 to the corrected value. Is a fine cellulose fiber dispersion according to <9>, in which all are 0.020 or less.
<11> Dry to dry at least one of the fine cellulose fiber dispersion produced by the production method according to <7> and the fine cellulose fiber dispersion according to any one of <8> to <10>. It is a manufacturing method of the fine cellulose fiber characterized by including a process.
<12> A fine cellulose fiber produced by the production method according to <11>.
<13> At least one of the fine cellulose fiber dispersion produced by the production method according to <7> and the fine cellulose fiber dispersion according to any one of <8> to <10> is formed into a predetermined shape. It is a manufacturing method of the fine cellulose fiber molded object characterized by removing a liquid component, hold | maintaining.
<14> A fine cellulose fiber molded article produced by the production method according to <13>.
<15> A fine cellulose fiber dispersion produced by the production method according to <7>, and at least one of the fine cellulose fiber dispersion according to any one of <8> to <10>, and a composite A method for producing a fine cellulose fiber composite comprising using a dispersion obtained by mixing a liquid material containing a material.
<16> A fine cellulose fiber composite produced by the production method according to <15>.

Claims

An oxidation step of oxidizing cellulose raw material in a reaction solution containing an N-oxyl compound and a co-oxidant to obtain oxidized cellulose fibers;
A reduction step of reducing the oxidized cellulose fibers in a reaction solution containing a reducing agent to obtain reduced oxidized cellulose fibers;
A drying step of drying the reduced oxidized cellulose fiber,
A method for producing a cellulose fiber, wherein the cellulose fiber obtained by drying the reduced oxidized cellulose fiber can be finely dispersed in a solvent.
The manufacturing method of the cellulose fiber of Claim 1 including the additional oxidation process which further oxidizes the oxidized cellulose fiber obtained at the oxidation process with sodium chlorite between an oxidation process and a reduction | restoration process.
3. The method for producing cellulose fiber according to claim 1, wherein the pH of the reaction solution in the reduction step is 9 to 10.
A cellulose fiber produced by the production method according to claim 1 and finely dispersible in a solvent.
Cellulose fibers that can be finely dispersed in a solvent after drying,
After drying the cellulose fiber at 105 ° C. for 3 hours, the cellulose fiber is diluted with water to a concentration of 0.1% by mass to obtain a 40 mL dispersion, and the dispersion is placed in a 50 mL container. After defibrating for 2 minutes at 7,500 rpm using a cylindrical homogenizer, when the fiber is defibrated for 8 minutes with an ultrasonic homogenizer while cooling around the vessel with ice water, the light transmittance at a wavelength of 600 nm of the dispersion is Cellulose fiber characterized by having a birefringence of 80% or more.
After the cellulose fibers are dried at 105 ° C. for 3 hours, the cellulose fibers are diluted with water to a concentration of 0.1% by mass to form a 40 mL dispersion, and the dispersion is placed in a 50 mL container. After defibrating for 2 minutes at 7,500 rpm using a mold homogenizer, defibrating for 8 minutes with an ultrasonic homogenizer while cooling around the container with ice water, and then removing undefibrated cellulose fibers in the dispersion. A cast film is prepared using the obtained dispersion, and the cast film is dried at 105 ° C. for 3 hours to obtain a dry cast film. Absorbance at wavelengths of 290 nm and 260 nm when the ultraviolet absorption spectrum of the dry cast film is measured. Is a value obtained by correcting the absorbance per 1 μm thickness of the dry cast film (however, the ultraviolet absorption spectrum is In the measurement of Torr, when absorption at 235 nm derived from hexeneuronic acid groups was observed, the value obtained by correcting the absorbance at 260 nm to the absorbance per 1 μm thickness of the dry cast film was 0 to the corrected value. 6. The cellulose fiber according to any one of claims 4 to 5, wherein all are 0.020 or less.
A dispersion step of dispersing at least one of the cellulose fiber produced by the method for producing a cellulose fiber according to any one of claims 1 to 3 and the cellulose fiber according to any one of claims 4 to 6 in a solvent is included. The manufacturing method of the fine cellulose fiber dispersion characterized by the above-mentioned.
A fine cellulose fiber dispersion in which cellulose fibers are finely dispersed in a solvent,
The cellulose fiber is a cellulose fiber that can be finely dispersed in a solvent after drying,
After drying the cellulose fiber at 105 ° C. for 3 hours, the cellulose fiber is diluted with water to a concentration of 0.1% by mass to obtain a 40 mL dispersion, and the dispersion is placed in a 50 mL container. After defibrating for 2 minutes at 7,500 rpm using a cylindrical homogenizer, when the fiber is defibrated for 8 minutes with an ultrasonic homogenizer while cooling around the vessel with ice water, the light transmittance at a wavelength of 600 nm of the dispersion is A fine cellulose fiber dispersion which is 80% or more and exhibits birefringence.
After the cellulose fibers are dried at 105 ° C. for 3 hours, the cellulose fibers are diluted with water to a concentration of 0.1% by mass to form a 40 mL dispersion, and the dispersion is placed in a 50 mL container. After defibrating for 2 minutes at 7,500 rpm using a mold homogenizer, defibrating for 8 minutes with an ultrasonic homogenizer while cooling around the container with ice water, and then removing undefibrated cellulose fibers in the dispersion. A cast film is prepared using the obtained dispersion, and the cast film is dried at 105 ° C. for 3 hours to obtain a dry cast film. Absorbance at wavelengths of 290 nm and 260 nm when the ultraviolet absorption spectrum of the dry cast film is measured. Is a value obtained by correcting the absorbance per 1 μm thickness of the dry cast film (however, the ultraviolet absorption spectrum is In the measurement of Torr, when absorption at 235 nm derived from hexeneuronic acid groups was observed, the value obtained by correcting the absorbance at 260 nm to the absorbance per 1 μm thickness of the dry cast film was 0 to the corrected value. The fine cellulose fiber dispersion according to claim 8, wherein all are 0.020 or less.
It includes a drying step of drying at least one of the fine cellulose fiber dispersion produced by the production method according to claim 7 and the fine cellulose fiber dispersion according to any one of claims 8 to 9. A method for producing fine cellulose fibers.