JP2015196693A - Fine cellulose fiber dispersion, manufacturing method thereof and cellulose laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide fine cellulose fiber dispersion capable of suppressing humidity deterioration and also to provide a cellulose laminate obtained from a fine cellulose fiber having improved water proofness.SOLUTION: Fine cellulose fiber dispersion is fluid dispersion including a cellulose fiber to which a carboxyl group is introduced, and an organic solvent. The carboxyl group includes an alkali ion as a counter ion.

Description

  TECHNICAL FIELD The present invention relates to a fine cellulose fiber dispersion and a technique relating to fine cellulose fibers that can be used as a functional film substrate, a coating agent, or various additives.

In recent years, with increasing interest in environmental issues, natural polysaccharides such as starch, cellulose and chitin chitosan and their derivatives have attracted attention as biomass materials for conventional petroleum resins. In addition, a substrate made of a biodegradable resin that can be decomposed into water and carbon dioxide in the environment has attracted attention and is commercially available. Specifically, raw materials are aliphatic polyesters produced by microorganisms, naturally occurring starches, various polysaccharides such as cellulose and chitin chitosan and their derivatives, biodegradable resins and starches obtained by completely chemical synthesis. Examples include polylactic acid obtained by polymerizing the obtained lactic acid.
Among these, cellulose produced in large quantities on the earth is fibrous and has high crystallinity, high strength and low linear expansion, and excellent chemical stability and safety to living bodies. Therefore, it is attracting attention as a functional material. In particular, fine cellulose fibers have recently been actively developed for use in paper strength enhancers, filter aids, food additives, and the like.

As a method for producing fine cellulose fibers, for example, Patent Document 1 describes a method of defibration (miniaturization) by ejecting a cellulose suspension from a high-pressure atmosphere of 100 MPa or more and reducing the pressure.
Patent Document 2 describes a method of obtaining fine cellulose fibers by dispersing cellulose, in which a part of hydroxyl groups are oxidized to carboxyl groups, in a medium. According to this method, it is possible to relatively easily obtain fine cellulose fibers by utilizing the electric repulsion action of a carboxyl group having a negative charge.

JP 2009-155572 A JP 2008-1728 A

  Patent Document 1 describes that a fine cellulose fiber having an average fiber diameter of 4 to 200 nm can be obtained. However, an apparatus that can be used requires a very high pressure and a plurality of treatments for defibration. Limited. In addition, it is difficult to efficiently obtain uniform fine cellulose fibers only by mechanical treatment. Moreover, the use of the obtained fine cellulose fiber is only described about the compounding with the synthetic polymer, and the fine cellulose fiber alone is not shown.

Moreover, in the method of patent document 2, as described in the Example, a carboxyl group has metal ions, such as a sodium ion, as a counter ion. When trying to use fine cellulose fibers for a barrier layer such as a packaging film, the inclusion of these metal ions adversely affects the moisture resistance, so it is not preferable to contain metal ions. Moreover, although it is described that these fine cellulose fibers are used as an aqueous dispersion, the fiber membrane obtained by drying the aqueous dispersion has binding water between the fibers, and is completely removed from the fiber membrane. I can't pull it out. For this reason, there is a problem that water vapor tends to enter the film under high humidity and is easily affected by humidity. Further, when the fiber dispersion is obtained by drying the aqueous dispersion, it is disadvantageous in terms of energy.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a fine cellulose fiber dispersion that is less susceptible to humidity deterioration. Moreover, it aims at providing the cellulose laminated body obtained from the fine cellulose fiber with improved water resistance.

In order to solve the above problem, a fine cellulose fiber dispersion according to one embodiment of the present invention is a dispersion containing a cellulose fiber into which a carboxyl group is introduced and an organic solvent, and the carboxyl group is used as a counter ion. It is a carboxyl group containing alkali ions.
Further, the method for producing a fine cellulose fiber dispersion according to another aspect of the present invention includes a step of obtaining an oxidized cellulose fiber suspension in which carbosyl groups are introduced by oxidizing cellulose, and an acid is added to the oxidized cellulose fiber suspension. And converting the carboxyl group from a salt state to a carboxylic acid and an aqueous medium containing oxidized cellulose fibers in which the carboxyl group is converted to a carboxylic acid into a cellulose fiber solution having a pH of 4 or more and a pH of 12 or less using an alkali. A step of adjusting, a step of solvent-substituting a cellulose fiber solution having a pH of 4 to 12 with an organic solvent, and a step of dispersing the solvent-substituted cellulose fiber solution to prepare a fine cellulose fiber dispersion. It is characterized by that.

According to the present invention, it is possible to obtain a uniform fine cellulose fiber dispersion by effectively using cellulose, which is a natural resource that is biodegradable and has a small environmental load in disposal.
From the fine cellulose fiber dispersion according to the present invention, a cellulose film having high heat resistance, low linear expansion coefficient, high elastic modulus, high strength and high transparency and improved water resistance can be produced. This can be used for packaging materials, particularly gas barrier materials or structures. Moreover, since the inorganic alkali used conventionally is not used in the dispersion process, it is also suitable for electronic member applications that do not like mixing of metal ions such as sodium. Further, the dispersion can be combined with various resins by using it as a coating agent or additive.

It is a figure explaining the cellulose laminated body which concerns on embodiment based on this invention.

Embodiments according to the present invention will be described below.
(Fine cellulose fiber dispersion)
The fine cellulose fiber dispersion of the present embodiment includes cellulose fibers having an introduced carboxyl group and an organic solvent, and the carboxyl group is a carboxyl group containing an alkali ion as a counter ion.
The cellulose fiber into which the carboxyl group is introduced preferably has a carboxyl group content of 0.1 mmol / g or more and 2 mmol / g or less. The alkali may be any of amines or quaternary ammonium compounds having a hydroxide ion as a counter ion. As the organic solvent, alcohol, ketone, ether or the like may be employed. The cellulose fiber introduced with a carboxyl group preferably has a number average fiber diameter of 0.001 μm or more and 0.050 μm or less.

(Production method)
The fine cellulose fiber dispersion of this embodiment is produced by, for example, the following method.
First, a carboxyl group is introduced into cellulose as a raw material.
(material)
As a raw material, naturally-derived cellulose having a crystal structure of cellulose I can be used. Examples of naturally occurring cellulose as a raw material include wood pulp, non-wood pulp, cotton pulp, bacterial cellulose, and squirt cellulose.

(Oxidation method)
Cellulose is oxidized to introduce carbosyl groups into the cellulose.
The cellulose oxidation method can be appropriately selected from generally known methods for introducing a carboxyl group from a hydroxyl group via an aldehyde.
Among them, a method using a nitroxy radical derivative as a catalyst and using a hypohalite or a halite as a co-oxidant is preferable. In particular, an aqueous medium containing sodium hypochlorite and sodium bromide using TEMPO (2,2,6,6-tetramethylpiperidinooxy radical) as a catalyst under alkaline conditions, preferably in the range of pH 9 to pH 11 The TEMPO oxidation method carried out in the method is preferable from the viewpoint of availability of reagents, cost, and stability of the reaction. In the above TEMPO oxidation method, alkali is consumed as the reaction proceeds, so it is preferable to add an aqueous alkaline solution as needed to keep the pH in the system constant.

In TEMPO oxidation, the 6-position hydroxyl group of the pyranose ring (glucose) of the cellulose molecule is selectively oxidized, and a carboxyl group can be introduced via an aldehyde group. In addition, in TEMPO oxidation using natural cellulose, oxidation occurs only on the surface of crystalline microfibrils, which is a structural unit of cellulose, and no oxidation occurs inside the crystal. For this reason, it is possible to obtain fine cellulose fibers while maintaining the crystal structure of cellulose I, and the fine cellulose fibers to be produced have characteristics such as high heat resistance, low linear expansion coefficient, high elastic modulus, high strength, and gas barrier properties. Have
Reagents used for TEMPO oxidation are easily available commercially. The reaction temperature is preferably 0 ° C. or more and 60 ° C. or less, and a sufficient amount of carboxyl groups can be introduced to form fine fibers and exhibit dispersibility in about 1 to 12 hours.
TEMPOs and sodium bromide may be used in an amount as a catalyst during the reaction, and can also be recovered after the reaction. In the above reaction system, sodium chloride is the only theoretical by-product, and the waste liquid can be easily treated with a low environmental burden.

The amount of the carboxyl group can be adjusted by appropriately setting the TEMPO oxidation conditions. Cellulose fibers are dispersed in the medium by the electric repulsive force of the carboxyl group. Therefore, if the content of the carboxyl group is too small, it cannot be stably dispersed in the medium. On the other hand, if the amount is too large, the affinity for water increases and the water resistance decreases. In this respect, the carboxyl group content is preferably 0.1 mmol / g or more and 2 mmol / g or less, and more preferably 0.6 mmol / g or more and 2 mmol / g or less. In the process of introducing the carboxyl group, an aldehyde group that is an intermediate of the oxidation reaction is generated, and the aldehyde group remains in the final product. When the content of the aldehyde group is too large, the dispersibility in the aqueous medium is lowered. Therefore, the content of the aldehyde group is preferably 0.01 mmol / g or more and 0.3 mmol / g or less.
The oxidation reaction is stopped by adding an excessive amount of other alcohol to completely consume the cooxidant in the system. As the alcohol to be added, it is desirable to use a low molecular weight alcohol such as methanol, ethanol or propanol in order to quickly terminate the reaction. Among these, ethanol is preferable in consideration of safety and by-products generated by oxidation.

(Recovery of oxidized cellulose)
When recovering the oxidized cellulose, an acid is added to convert the carbosyl group from a salt state to a carboxylic acid state.
After the oxidation reaction is stopped, the produced oxidized cellulose can be recovered from the reaction solution by filtration. In the oxidized cellulose after the reaction is stopped, the carboxyl group forms a salt with a metal ion as a counter ion.
When recovering the oxidized cellulose, a dilute solution such as hydrochloric acid is added to the suspension of oxidized cellulose to adjust the pH to 2 or more and 3 or less to convert the carboxyl group of the oxidized cellulose from a salt state to a carboxylic acid. Thereafter, it is filtered off. Such a method is preferable in terms of handling properties, yield, and waste liquid treatment. Moreover, most of the counter ions (metal ions) in the oxidized cellulose can be removed by once converting to carboxylic acid.
The metal ion content contained in the oxidized cellulose can be examined by various analysis methods. For example, it can be simply examined by elemental analysis using an EPMA method or an X-ray fluorescence analysis method using an electron beam microanalyzer. be able to. When recovered by the method of filtering while forming a salt, the content of metal ions is 5 wt% or more, whereas when recovered by the method of filtering after carboxylic acid, the metal ion content is 1 wt%. It becomes as follows.

(Washing)
The recovered oxidized cellulose can be purified by repeated washing, and residues such as catalyst, salt and ions can be removed. The cleaning liquid is preferably water. If salt or the like remains in the cellulose, it is difficult to disperse in the dispersion step described later, and therefore, it is preferable to perform washing multiple times.

(Adjustment process)
Washing is performed, and the oxidized cellulose from which the salt has been removed is adjusted to pH 4 to pH 12 using an alkali in an aqueous medium and stirred. As a result, the carboxyl group of the oxidized cellulose is returned from the carboxylic acid state to the salt state.
As an alkali, in order to avoid that a metal ion is accompanied by a dispersion liquid, pH is adjusted using ammonia water or an organic alkali. Organic alkalis include various aliphatic amines, aromatic amines, amines such as diamines, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide, benzyltrimethylammonium hydroxide, 2-hydroxyhydroxide. Examples thereof include quaternary ammonium compounds having a hydroxide ion represented by NR4OH (R is an alkyl group, a benzyl group, a phenyl group, or a hydroxyalkyl group) such as ethyltrimethylammonium as a counter ion. Even when an organic alkali is used, it is possible to refine the fiber by a dispersion treatment similar to that when an inorganic alkali is used, regardless of the type of alkali.

(Solvent replacement process)
Next, when pH becomes constant, the oxidized cellulose is drained with a nylon mesh, and water is squeezed out as much as possible. The obtained oxidized cellulose is suspended in an organic solvent, stirred, and again drained with a nylon mesh. By repeating this operation a plurality of times, water contained in the oxidized cellulose can be removed.
Next, before the step of refining the oxidized cellulose, first, the oxidized cellulose that has been subjected to the solvent replacement treatment is immersed in an organic solvent that is a dispersion medium.
At this time, the pH of the immersed liquid is, for example, 4 or less. Oxidized cellulose is insoluble in organic solvents and becomes a non-uniform suspension when immersed.

(Miniaturization process)
It refines | miniaturizes by carrying out the dispersion process of an oxidized cellulose in the organic solvent.
As a method for dispersion treatment in an organic solvent, various known dispersion treatments are possible. For example, homomixer processing, mixer processing with rotary blade, high pressure homogenizer processing, ultra high pressure homogenizer processing, ultrasonic homogenizer processing, nanogenizer processing, disc type refiner processing, conical type refiner processing, double disc type refiner processing, grinder processing, ball mill processing And underwater facing processing. Among these, the mixer treatment with a rotary blade, the high-pressure homogenizer treatment, the ultra-high pressure homogenizer treatment, and the ultrasonic homogenizer treatment are preferable from the viewpoint of miniaturization efficiency. In addition, it is also possible to perform dispersion by combining two or more processing methods among these processes.

When ammonia is used as an alkali during the dispersion treatment, the temperature rises due to the heat generated in the dispersion treatment, and the ammonia is volatilized, so that the counter ion of the carboxyl group is partially replaced with H. When the electrostatic repulsion between the carboxyl groups is no longer obtained, it becomes difficult to disperse. Therefore, when ammonia is used, the dispersion treatment is preferably performed while cooling in order to prevent the temperature from rising during the dispersion.
When the dispersion treatment is performed, the suspension becomes a visually transparent dispersion liquid. Oxidized cellulose is refined by the dispersion treatment to form fine cellulose fibers. The fine cellulose fibers after the dispersion treatment preferably have a number average fiber diameter (width in the minor axis direction of the fibers) of 0.001 μm or more and 0.050 μm or less. The fiber diameter of the fine cellulose fiber can be confirmed with a scanning electron microscope (SEM) or an atomic force microscope (AFM). If the dispersion is insufficient or non-uniform and some of the fibers have large diameters, the transparency, smoothness, and gas barrier properties of the film will be significantly reduced when the dispersion is formed. is there.

(Cellulose laminate)
As shown in FIG. 1, a cellulose laminate is formed by applying the fine cellulose fiber dispersion described above to at least one surface of a substrate 1 to form a film 2.
It is possible to form a self-supporting film of a cellulose film from a fine cellulose fiber dispersion by a method such as casting or forming a film on a base material by coating and extrusion, followed by drying and peeling. When forming this cellulose film, the lower the boiling point of the solvent, the easier it is to dry and the better the energy efficiency.
By drying the coated film with an oven or the like, a film of fine cellulose fibers can be formed on the substrate. At this time, in order to reduce the surface tension of the coating film to suppress the repelling and to reduce the drying energy, it is preferable that the dispersion medium is alcohol. For the same reason as described above, the mechanical strength and gas barrier properties of the coating film can also be improved. The alcohol is preferably a low molecular weight alcohol. Furthermore, in order to improve the adhesion to the substrate, a surface modification treatment such as corona discharge treatment, plasma treatment, or ultraviolet irradiation may be applied to the substrate in advance.

In forming the cellulose film or laminate of the present embodiment, a compound having a reactive functional group such as amino group, epoxy group, hydroxyl group, carbodiimide group, polyethyleneimine, or isocyanate is added to the fine cellulose fiber dispersion as an additive. You may do it. These additives react with hydroxyl groups, carboxyl groups, and aldehyde groups in the oxidized cellulose, and are effective in improving the performance of the coating, particularly film strength, water resistance, moisture resistance, or adhesion to the substrate. Further, an inorganic layered compound may be added and used as an additive. The inorganic layered compound refers to a crystalline inorganic compound having a layered structure, and examples thereof include clay minerals represented by kaolinite group, smectite group, mica group and the like. As long as it is an inorganic layered compound, its type, particle size, aspect ratio and the like can be appropriately selected according to the required characteristics, and are not particularly limited. In general, examples of the smectite group inorganic layered compound include montmorillonite, hectorite, saponite and the like. I can give you. Addition of an inorganic layered favorite is particularly effective in improving gas barrier properties. In addition, additives such as pigments, dyes, and dispersants can be blended at a level that does not impair the effects of the present invention.
Furthermore, you may provide ceramic vapor deposition layers, such as a thermoplastic resin layer, a printing layer, a protective layer, etc. which enable a heat seal further to the above-mentioned cellulose film and laminated body as needed.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to the following Example.
(Preparation method of oxidized cellulose)
Softwood bleached pulp, which is widely available as cellulose, was used.
30 g of cellulose (in terms of dry mass) was added to 600 g of distilled water, stirred and swollen, and then defibrated with a mixer. To this, 1200 g of distilled water and 0.3 g of TEMPO dissolved in 200 g of distilled water in advance and 3 g of sodium bromide were added, and 86 g of a 2 mol / L sodium hypochlorite aqueous solution was added dropwise to oxidize the reaction. Started. The reaction temperature was always kept below 20 ° C. During the reaction, the pH in the system was lowered, but a 0.5 N NaOH aqueous solution was sequentially added to adjust the pH to 10. And when it was made to react for 3 hours, ethanol 30g was added and reaction was stopped. Subsequently, 0.5N HCl was added dropwise to the reaction solution to lower the pH to 2.
The reaction solution was filtered using a nylon mesh, and the solid content was further washed several times with water to remove the reaction reagent and by-products, thereby obtaining oxidized cellulose containing water with a solid content concentration of 7%.

(Measurement of the amount of functional groups introduced)
0.2 g of wet oxidized cellulose in terms of absolute dry mass was weighed into a beaker and distilled water was added to make 60 g. 0.5 mL of 0.1 M NaCl aqueous solution was added, the pH was adjusted to 3 with 0.5 M hydrochloric acid, and 0.5 M NaOH aqueous solution was dropped to conduct conductivity measurement. The measurement was continued until the pH reached about 11. Since the portion corresponding to the neutralization stage of the weak acid is the amount of carboxyl groups, the amount of carboxyl groups was 1.6 mmol / g when the addition amount of NaOH was read from the obtained conductivity curve.
Next, 20 g of 0.5 M acetic acid, 60 mL of distilled water and 1.8 g of sodium chlorite were added to 2 g of wet oxidized cellulose in terms of absolute dry mass, adjusted to pH 4 and reacted for 48 hours. Thereafter, the amount of carboxyl groups was measured by the same method as described above, and it was 1.8 mmol / g. From this, the aldehyde group amount was calculated to be 0.2 mmol / g.

<Example 1>
(Preparation of fine cellulose fiber dispersion)
Distilled water was added to 57.14 g (4 g solid content) of oxidized cellulose having a solid content concentration of 7% prepared as described above to obtain a 400 g oxidized cellulose suspension. The pH was adjusted to 9 using 0.1 mol / l aqueous ammonia. After stirring for 30 minutes, the recovered pulp was suspended in ethanol after dehydration with a nylon mesh. Subsequently, the liquid removal / recovery operation was repeated again. The obtained pulp was suspended again in ethanol and treated with an ultrasonic homogenizer for 20 minutes to obtain a fine cellulose fiber dispersion.
<Example 2>
(Preparation of fine cellulose fiber dispersion)
Distilled water was added to 57.14 g (4 g solid content) of oxidized cellulose having a solid content concentration of 7% prepared as described above to obtain a 400 g oxidized cellulose suspension. The pH was adjusted to 9 using 10 wt% tetraethylammonium hydroxide. Thereafter, the same operation was performed to obtain a fine cellulose dispersion of ethanol.

<Comparative Example 1>
(Preparation of fine cellulose fiber dispersion)
Distilled water was added to 57.14 g (4 g solid content) of oxidized cellulose having a solid content concentration of 7% prepared as described above to obtain a 400 g oxidized cellulose suspension. The pH was adjusted to 9 using an aqueous sodium hydroxide solution. The prepared dispersion was treated with an ultrasonic homogenizer for 20 minutes to obtain a fine cellulose fiber dispersion.
(Cellulose coating film)
The fine cellulose fiber dispersions of Examples 1 and 2 and Comparative Example 1 were coated on a PET film (E5102 manufactured by Toyobo Co., Ltd.) with a bar coater, and then dried at 120 degrees for 30 minutes to obtain a cellulose having a dry film thickness of 1 μm. A coated film was obtained.
(Measurement of sodium ion content)
The amount of sodium ions in the cellulose film was measured by the EPMA method using an X-ray microanalyzer.
[Oxygen permeability (isobaric method) (cm 3 / m 2 · day · Pa)]
Measurement was performed in an atmosphere of 30 ° C., 40% RH and 70% RH using an oxygen permeability measuring device MOCON (OX-TRAN 2/21, manufactured by Modern Control).
Table 1 shows the results of measuring the transmittance of the dispersions of Examples 1 and 2 and Comparative Example 1, and the sodium ion content and oxygen permeability of the cellulose film.

  As shown in the results, when sodium hydroxide is used as the alkali and water is used as the dispersion medium, the oxygen permeability under high humidity is greatly deteriorated. In Examples 1 and 2 using ethanol as the dispersion medium, the deterioration of the barrier property under high humidity could be suppressed to a smaller level.

DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Cellulose layer

Claims (8)

A cellulose fiber having an introduced carboxyl group and an organic solvent,
The fine cellulose fiber dispersion liquid, wherein the carboxyl group is a carboxyl group containing an alkali ion as a counter ion.   2. The fine cellulose fiber dispersion according to claim 1, wherein the cellulose fiber introduced with the carboxyl group has a carboxyl group content of 0.1 mmol / g or more and 2 mmol / g or less.   The fine cellulose fiber dispersion liquid according to claim 1 or 2, wherein the alkali is either an amine or a quaternary ammonium compound having a hydroxide ion as a counter ion.   The said organic solvent is an organic solvent containing at least one of alcohol, a ketone, and ether, The fine cellulose fiber dispersion liquid of any one of Claims 1-3 characterized by the above-mentioned.   The fine cellulose fiber dispersion according to any one of claims 1 to 4, wherein the cellulose fiber into which the carboxyl group is introduced has a number average fiber diameter of 0.001 µm or more and 0.050 µm or less. liquid.   The fine cellulose fiber dispersion according to any one of claims 1 to 5 is applied to at least one surface on a base material to form a film on the base material. Cellulose laminate. A step of oxidizing cellulose to obtain an oxidized cellulose fiber suspension introduced with carbosyl groups;
Adding an acid to the oxidized cellulose fiber suspension to convert the carboxyl group from a salt state to a carboxylic acid;
Adjusting the aqueous medium containing oxidized cellulose fibers in which carboxylate is converted to carboxylic acid to a cellulose fiber solution having a pH of 4 or more and a pH of 12 or less using an alkali;
a step of solvent-substituting a cellulose fiber solution having a pH of 4 to 12 with an organic solvent;
Dispersing the solvent-substituted cellulose fiber solution to prepare a fine cellulose fiber dispersion,
The manufacturing method of the fine cellulose fiber dispersion liquid characterized by comprising.   The method for producing a fine cellulose fiber dispersion according to claim 7, wherein the dispersion treatment is any one of a mixer treatment with a rotary blade, a high-pressure homogenizer treatment, an ultra-high pressure homogenizer treatment, and an ultrasonic homogenizer treatment.

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