JP2024101346A - Method for producing chemical modification fine cellulose fiber - Google Patents

Abstract

To provide a method for producing a homogeneous chemical modification fine cellulose fiber from a raw material pulp, as well as, a method for producing a resin composition imparting a compact excellent in appearance, smoothness and mechanical characteristics due to homogeneous fine dispersion of the chemical modification fine cellulose fiber in the resin.SOLUTION: A method for producing a chemical modification fine cellulose comprises a modification step of chemically modifying the raw material pulp to the inside of the fiber in a slurry containing the raw material pulp to obtain a chemically modified pulp, and a defibrillation step comprising defibrillating the chemically modified pulp to produce a chemically modified fine cellulose fiber, wherein the raw material pulp has an average fiber diameter of more than 1 μm, a solid content concentration of the slurry is 4 mass% or more, and the moisture content of the slurry is less than 6 mass% through the modification step.SELECTED DRAWING: None

Description

The present invention relates to a method for producing chemically modified fine cellulose fibers, and a method for producing a resin composition containing chemically modified fine cellulose fibers.

Thermoplastic resins are light and have excellent processing properties, and are therefore widely used in a wide range of applications, including automotive components, electrical and electronic components, office equipment housings, and precision components. However, resins alone often have insufficient mechanical properties and dimensional stability, and so composites of resins and various fillers are generally used. In recent years, the use of organic fibers such as cellulose fibers as such fillers has been considered. Cellulose is a promising filler for environmentally friendly resin compositions because it is a material that places little strain on the environment, has a low specific gravity, and can have an excellent effect of improving the physical properties of resin compositions. In particular, fine cellulose fibers can exhibit excellent reinforcing effects on resin compositions even in small amounts due to their fine structure, and therefore their use as fillers for resin compositions has been considered in recent years. However, fine cellulose fibers are extremely prone to aggregation due to hydrogen bonds between cellulose molecules, and uniform dispersion in resin is not necessarily easy. In order to achieve excellent reinforcing effects in the fine cellulose fibers and to disperse the fine cellulose fibers well in resin, various techniques have been proposed in the past in which fine cellulose fibers are hydrophobized by chemical modification and then mixed with resin. The uniformity of the degree of substitution of chemically modified cellulose is an important factor, as it is closely related to the compatibility of fine cellulose fibers with resins and the dispersibility of fine cellulose fibers in resins.

For this reason, the most common method for producing chemically modified fine cellulose fibers is to chemically modify fine cellulose fibers obtained by defibrating pulp, a coarse fiber containing cellulose. However, methods for chemically modifying fine cellulose fibers have productivity issues, such as the need to produce them at a low solids content due to the high viscosity of the slurry, and the slow filtration rate during purification after chemical modification.

On the other hand, in order to improve productivity, a method of obtaining fine fibers by chemically modifying coarse cellulose fibers and then refining and defibrating them has been studied. For example, Patent Document 1 describes a method of obtaining carboxymethylated fine fibers by using a twin-shaft kneader to carry out a mercerization reaction of hardwood pulp in a solvent mainly composed of water, followed by a carboxymethylation reaction in a mixed solvent of water and an organic solvent, to obtain high solid fraction, and then defibrating the carboxymethylated cellulose produced by the reaction. Patent Document 2 describes a method of impregnating softwood kraft pulp with a mixed aqueous solution of ammonium dihydrogen phosphate and urea, heat treating the pulp to introduce phosphoric acid groups into the cellulose in the pulp to obtain phosphorylated pulp, adding water to the phosphorylated pulp obtained, and defibrating and drying the resulting pulp suspension in a wet atomizer to obtain cellulose fine fibers.

JP 2019-206607 A JP 2017-066274 A

Conventional methods have had the problem that it is difficult for chemical modifiers to penetrate into the interior of the pulp, and the degree of substitution of the chemical modification varies greatly between the surface and the interior of the pulp. In particular, the higher the purity and crystallinity of the cellulose, which is effective as a filler, the more difficult it is to achieve a uniform degree of substitution.

The present invention aims to solve the above problems and provide a method for producing uniform chemically modified fine cellulose fibers from raw pulp, and a method for producing a resin composition in which the chemically modified fine cellulose fibers are uniformly finely dispersed in a resin, thereby producing a molded article with excellent appearance, smoothness, and mechanical properties.

This disclosure includes the following items:
[Item 1]
a modification step in which the raw pulp is chemically modified to the inside of the fibers in a slurry containing the raw pulp, an aprotic polar solvent, a modifying agent which is an esterifying agent, and a catalyst to obtain a chemically modified pulp; and a defibration step in which the chemically modified pulp is defibrated to produce chemically modified fine cellulose fibers.
A method for producing chemically modified fine cellulose fibers, comprising:
The raw pulp has an average fiber diameter of more than 1 μm,
The solid content of the slurry is 4% by mass or more,
The method, wherein the moisture content of the slurry is less than 6% by mass throughout the modification step.
[Item 2]
Further comprising a dehydration step prior to the modification step,
2. The method according to item 1, wherein the dewatering step is a step of adjusting the moisture content of one or more selected from the group consisting of the raw pulp, the aprotic polar solvent, the modifying agent, the catalyst, and the slurry to 1 mass % or less by one or more selected from the group consisting of temperature control, pressure control, humidity control, and use of a dewatering agent.
[Item 3]
In the dehydration step, the water content of the aprotic polar solvent is adjusted to 1% by mass or less;
3. The method according to item 2, wherein the moisture content of the slurry is 1% by mass or less throughout the modification process.
[Item 4]
4. The method according to any one of items 1 to 3, wherein the interfibril distance of the raw pulp in the slurry subjected to the modification step is 10 nm or more.
[Item 5]
5. The method according to any one of items 1 to 4, wherein the aprotic polar solvent comprises one or more selected from the group consisting of ketones, esters, nitrogen-containing compounds, sulfur-containing compounds, ethers, and halogenated hydrocarbons.
[Item 6]
The raw pulp has an average fiber length of 500 μm or more and an average fiber diameter of 20 μm or more, and has the following characteristics (1) to (4):
(1) Crystallinity of 50% or more,
(2) a weight average molecular weight (Mw) of 100,000 or more, and a weight average molecular weight (Mw)/number average molecular weight (Mn) ratio of 6 or less,
(3) average acid-insoluble component content of 10% by mass or less, and (4) average alkali-soluble polysaccharide content of 12% by mass or less,
6. The method according to any one of items 1 to 5, wherein one or more of the following conditions are satisfied:
[Item 7]
The method further comprises a filtering step of filtering the slurry after the modifying step,
7. The method according to any one of items 1 to 6, wherein the catalyst is an inorganic salt, and the concentration of the catalyst in the slurry obtained in the filtration step is 1% by mass or less.
[Item 8]
a filtration preparation step of adding a flocculant to the slurry after the modification step, and then draining the slurry to obtain a slurry having a flocculant content of 50 mass% or less;
a filtration step of filtering the slurry obtained in the filtration preparation step;
8. The method according to any one of items 1 to 7, further comprising:
[Item 9]
the esterification agent is a vinyl carboxylate;
The degree of substitution (DS) of the chemically modified pulp is 2.0 or less;
The degree of substitution (DS) of the chemically modified fine cellulose fiber is 0.8 to 1.8,
The method according to any one of items 1 to 8, wherein the coefficient of variation (CV) of the DS non-uniformity ratio in the chemically modified fine cellulose fiber is 20% or less.
[Item 10]
A method for producing a resin composition using the method for producing chemically modified fine cellulose fibers according to any one of items 1 to 9,
A method for producing a resin composition, in which in the defibration step of producing the chemically modified fine cellulose fibers, the chemically modified pulp and a resin are mixed and the chemically modified pulp is defibrated to produce a resin composition containing chemically modified fine cellulose fibers and a resin.
[Item 11]
A fiber forming step of producing chemically modified fine cellulose fibers by the method for producing chemically modified fine cellulose fibers according to any one of items 1 to 9, and a mixing step of mixing the chemically modified fine cellulose fibers with a resin to produce a resin composition.
A method for producing a resin composition comprising the steps of:

According to one aspect of the present invention, there can be provided a method for producing uniform chemically modified fine cellulose fibers from raw pulp, and a method for producing a resin composition in which the chemically modified fine cellulose fibers are uniformly finely dispersed in a resin, thereby providing a molded article with excellent appearance, smoothness, and mechanical properties.

The following describes exemplary embodiments of the present invention (hereinafter, abbreviated as "present embodiments"); however, the present invention is not limited to these embodiments. Note that, unless otherwise specified, the characteristic values of the present disclosure are values measured by the method described in the [Examples] section of the present disclosure or a method that will be understood by those skilled in the art to be equivalent thereto.

<Production method of chemically modified fine cellulose fiber>
One aspect of the present invention is
A modification step in which the raw pulp is chemically modified to the inside of the fiber in a slurry containing the raw pulp, an aprotic polar solvent, a modifier, and a catalyst to obtain a chemically modified pulp; and
A defibration step of defibrating the chemically modified pulp to produce chemically modified fine cellulose fibers;
The present invention also provides a method for producing chemically modified fine cellulose fibers, the method comprising the step of:
The raw pulp is composed of coarse fibers and in one embodiment has an average fiber diameter of more than 1 μm.
In one embodiment, the solids concentration of the slurry subjected to chemical modification is 4% by mass or more, and/or the moisture content of the slurry throughout the modification step is less than 6% by mass.
In one embodiment, the modifying agent is an esterifying agent.
In one embodiment, the method may further include a dehydration step before the modification step and/or a filtration step after the modification step. In one embodiment, the method may include a filtration preparation step before the filtration step.

According to the method of this embodiment, by controlling the moisture content of the slurry in the modification step, it is possible to obtain chemically modified pulp with uniform distribution of substituents with high productivity, even when the pulp is composed of highly pure and highly crystalline coarse fibers. The chemically modified fine cellulose fibers obtained by the method of this embodiment can be uniformly finely dispersed in resin while retaining the excellent reinforcing effect inherent to cellulose molecules, which is advantageous for producing a resin composition that gives a molded product with excellent appearance, smoothness, and mechanical properties.

Pulp is composed of coarse fibers containing cellulose, and is often in bulk form due to drying or compression during the production process. Coarse fibers have a small specific surface area, making it difficult for chemical modifiers to penetrate into the fibers. Therefore, chemically modified pulp obtained by conventional chemical modification methods has the problem that the degree of substitution differs greatly between the surface and the interior of the coarse fibers. This non-uniformity in the degree of substitution tends to be more pronounced the higher the purity and crystallinity of the cellulose in the pulp.

The inventors have surprisingly found that by using an aprotic polar solvent and performing chemical modification with a water content in the reaction system of less than 6% by mass, it is possible to reduce the non-uniformity of the degree of substitution between the surface and the interior of the pulp. Without being bound by theory, it is believed that this is because the aprotic polar solvent increases the interfibril distance of cellulose, allowing the modifier to penetrate into the interior of the pulp.

<Raw pulp>
As the pulp, wood pulp obtained from wood species (broadleaf or coniferous), non-wood pulp obtained from non-wood species (bamboo, hemp-based fiber, bagasse, kenaf, linter, etc.), and refined pulp thereof (refined linters, etc.) can be used. As the non-wood pulp, cotton-derived pulp including cotton linter pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, straw-derived pulp, etc. can be used. Cotton-derived pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp may each be refined pulp obtained from raw materials such as cotton lint, cotton linter, hemp-based abaca (e.g., from Ecuador or the Philippines), zaisal, bagasse, kenaf, bamboo, straw, etc., through a refining process such as delignification by cooking, a bleaching process, etc. The pulp is preferably pulp derived from cotton linters, since it can produce chemically modified fine cellulose fibers with high crystallinity and excellent mechanical properties. Pulp is essentially hydrophilic due to the contribution of hydroxyl groups of cellulose, and can often be hygroscopic. When pulp absorbs moisture, the efficiency and/or uniformity of the modification reaction in the modification step tends to be low. However, the method of the present embodiment allows the highly efficient and uniform modification reaction to proceed using such raw pulp by controlling the moisture content during the modification step.

<Aprotic polar solvent>
The aprotic polar solvent is a solvent that is a polar molecule that is not a hydrogen bond donor. In one embodiment, the aprotic polar solvent is selected from the group consisting of ketones, esters, nitrogen-containing compounds, sulfur-containing compounds, ethers, and halogenated hydrocarbons, and may be used alone or in combination of two or more.

Ketones include acetone, methyl ethyl ketone (MEK), cyclohexanone, etc.

Examples of esters include esters of carboxylic acids or carbonic acids and aliphatic alcohols, more specifically, methyl formate, methyl acetate, ethyl acetate, ethyl lactate, propylene carbonate, etc.

Examples of sulfur-containing compounds include alkyl sulfoxides, such as di-C1-4 alkyl sulfoxides such as dimethyl sulfoxide (DMSO), methyl ethyl sulfoxide, and diethyl sulfoxide.

Nitrogen-containing compounds include:
Alkylamides, for example, N,N-diC1-4 alkylformamides such as N,N-dimethylformamide (DMF) and N,N-diethylformamide; N,N-diC1-4 alkylacetamides such as N,N-dimethylacetamide (DMAc) and N,N-diethylacetamide;

Pyrrolidones, for example, pyrrolidones such as 2-pyrrolidone and 3-pyrrolidone; N-C1-4 alkylpyrrolidone such as N-methyl-2-pyrrolidone (NMP); etc.

As an aprotic polar solvent, dimethyl sulfoxide (DMSO) is particularly preferred from the viewpoint of obtaining good chemical modification efficiency.

The molecular weight of the aprotic polar solvent may, in one embodiment, be 50 or more, or 100 or more, or 300 or more, or 1000 or more, and in one embodiment, may be 2000 or less.

The boiling point of the aprotic polar solvent may, in one embodiment, be 100°C or more, or 110°C or more, or 120°C or more, or 150°C or more, or 180°C or more, and in one embodiment, may be 300°C or less, or 290°C or less, or 280°C or less, or 260°C or less, or 240°C or less.

The relative dielectric constant of the aprotic polar solvent at 25°C is, in one embodiment, 1 or more, or 2 or more, or 3 or more, or 5 or more, or 7 or more, and in one embodiment, 80 or less, or 70 or less, or 60 or less, or 50 or less.

As the aprotic polar solvent, a solvent that is inherently difficult to absorb moisture is preferable, but a solvent that is suitable for the production of chemically modified fine cellulose fibers due to its excellent effect of increasing the interfibril distance (e.g., dimethyl sulfoxide (DMSO) etc.) is usually a solvent that easily absorbs moisture. Here, a solvent that easily absorbs moisture means, in one aspect, a solvent that has hygroscopicity due to its compatibility with water. Here, a solvent that is compatible with water means a solvent that is transparent at 20°C when 10 parts by mass is dissolved in 100 parts by mass of water (specifically, the visible light transmittance at wavelengths of 360 nm to 830 nm is 90% or more as measured by a haze meter). In the method of this embodiment, by controlling the amount of moisture during the process, the chemical modification reaction can be smoothly advanced to the inside of the pulp even when such a solvent that easily absorbs moisture is used.

<Modifiers and Catalysts>
Examples of the chemically modified pulp and chemically modified fine cellulose fibers produced by the method of this embodiment include inorganic esters such as nitrate esters, sulfate esters, phosphate esters, silicate esters, and borate esters, and organic esters such as acetylation and propionylation. The chemically modified products may contain one or more types of modifying groups.

As a modifying agent, an esterifying agent (acylating agent) that reacts with the hydroxyl groups of cellulose can be used, and an acetylating agent is preferred. As an esterifying agent, acid halides, acid anhydrides, vinyl carboxylates, and carboxylic acids are preferred.

[Acid Halide]
The acid halide may be at least one selected from the group consisting of compounds represented by the following formula:
R ¹ -C(=O)-X
(In the formula, ^R1 represents an alkyl group having 1 to 24 carbon atoms, an alkenyl group having 2 to 24 carbon atoms, a cycloalkyl group having 3 to 24 carbon atoms, or an aryl group having 6 to 24 carbon atoms, and X represents Cl, Br, or I.)
Specific examples of acid halides include, but are not limited to, acetyl chloride, acetyl bromide, acetyl iodide, propionyl chloride, propionyl bromide, propionyl iodide, butyryl chloride, butyryl bromide, butyryl iodide, benzoyl chloride, benzoyl bromide, and benzoyl iodide. Among them, acid chlorides can be preferably used in terms of reactivity and handling. In addition, in the reaction of acid halides, one or more alkaline compounds may be added to act as a catalyst and neutralize the by-product acidic substances. Specific examples of alkaline compounds include, but are not limited to, tertiary amine compounds such as triethylamine and trimethylamine; and nitrogen-containing aromatic compounds such as pyridine and dimethylaminopyridine.

[Acid anhydride]
As the acid anhydride, any suitable acid anhydride can be used. For example,
Saturated aliphatic monocarboxylic acid anhydrides, such as acetic acid, propionic acid, (iso)butyric acid, and valeric acid; unsaturated aliphatic monocarboxylic acid anhydrides, such as (meth)acrylic acid and oleic acid;
Anhydrides of alicyclic monocarboxylic acids such as cyclohexanecarboxylic acid and tetrahydrobenzoic acid; anhydrides of aromatic monocarboxylic acids such as benzoic acid and 4-methylbenzoic acid;
Examples of dibasic carboxylic acid anhydrides include saturated aliphatic dicarboxylic acid anhydrides such as succinic anhydride and adipic acid, unsaturated aliphatic dicarboxylic acid anhydrides such as maleic anhydride and itaconic anhydride, alicyclic dicarboxylic acid anhydrides such as 1-cyclohexene-1,2-dicarboxylic acid anhydride, hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride, and aromatic dicarboxylic acid anhydrides such as phthalic anhydride and naphthalic anhydride;
Examples of the polybasic carboxylic acid anhydrides having three or more bases include polycarboxylic acids (anhydrides) such as trimellitic anhydride and pyromellitic anhydride.
In the reaction of an acid anhydride, one or more of acidic compounds such as sulfuric acid, hydrochloric acid, phosphoric acid, etc., or Lewis acids (for example, Lewis acid compounds represented by MYn, where M represents a semimetal element such as B, As, Ge, etc., or a base metal element such as Al, Bi, In, etc., or a transition metal element such as Ti, Zn, Cu, etc., or a lanthanoid element, n is an integer corresponding to the atomic valence of M and represents 2 or 3, and Y represents a halogen atom, OAc, _OCOCF3 , _ClO4 , _SbF6 , _PF6 , or _OSO2CF3 (OTf)), or alkaline compounds such as triethylamine, pyridine, etc. may be added as a _catalyst .

[Vinyl carboxylate]
The vinyl carboxylate may be represented by the following formula:
R-COO-CH= _CH2
{wherein R is any one of an alkyl group having 1 to 24 carbon atoms, an alkenyl group having 2 to 24 carbon atoms, a cycloalkyl group having 3 to 16 carbon atoms, and an aryl group having 6 to 24 carbon atoms.} is preferred. The vinyl carboxylate is more preferably at least one selected from the group consisting of vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl cyclohexanecarboxylate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl pivalate, vinyl octylate, divinyl adipate, vinyl methacrylate, vinyl crotonate, vinyl octylate, vinyl benzoate, and vinyl cinnamate. In the esterification reaction with a vinyl carboxylate, one or more catalysts selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates, alkali metal hydrogencarbonates, primary to tertiary amines, quaternary ammonium salts, imidazole and derivatives thereof, pyridine and derivatives thereof, and alkoxides may be added as a catalyst.

Examples of alkali metal hydroxides and alkaline earth metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide, etc. Examples of alkali metal carbonates, alkaline earth metal carbonates, and alkali metal hydrogen carbonates include lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, and cesium hydrogen carbonate, etc.

Primary, secondary and tertiary amines refer to primary, secondary and tertiary amines, and specific examples include ethylenediamine, diethylamine, proline, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethyl-1,3-propanediamine, N,N,N',N'-tetramethyl-1,6-hexanediamine, tris(3-dimethylaminopropyl)amine, N,N-dimethylcyclohexylamine and triethylamine.

Imidazole and its derivatives include 1-methylimidazole, 3-aminopropylimidazole, carbonyldiimidazole, etc.

Examples of pyridine and its derivatives include N,N-dimethyl-4-aminopyridine and picoline.

Examples of alkoxides include sodium methoxide, sodium ethoxide, and potassium t-butoxide.

[carboxylic acid]
The carboxylic acid may be at least one selected from the group consisting of compounds represented by the following formulas:
R-COOH
(In the formula, R represents an alkyl group having 1 to 16 carbon atoms, an alkenyl group having 2 to 16 carbon atoms, a cycloalkyl group having 3 to 16 carbon atoms, or an aryl group having 6 to 16 carbon atoms.)

Specific examples of carboxylic acids include at least one selected from the group consisting of acetic acid, propionic acid, butyric acid, caproic acid, cyclohexane carboxylic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, pivalic acid, methacrylic acid, crotonic acid, octylic acid, benzoic acid, and cinnamic acid.

Among these carboxylic acids, at least one selected from the group consisting of acetic acid, propionic acid, and butyric acid, and particularly acetic acid, is preferred from the viewpoint of reaction efficiency.
In the reaction of carboxylic acid, one or more kinds of acidic compounds such as sulfuric acid, hydrochloric acid, phosphoric acid, etc., or Lewis acids (for example, Lewis acid compounds represented by MYn, where M represents a semimetal element such as B, As, Ge, etc., or a base metal element such as Al, Bi, In, etc., or a transition metal element such as Ti, Zn, Cu, etc., or a lanthanoid element, n is an integer corresponding to the atomic valence of M and represents 2 or 3, and Y represents a halogen atom, OAc, _OCOCF3 , _ClO4 , _SbF6 , _PF6 , or _OSO2CF3 (OTf)), or alkaline compounds such as triethylamine, pyridine, etc. may be added as _a catalyst.

Among these esterification reactants, at least one selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, vinyl acetate, vinyl propionate, vinyl butyrate, and acetic acid, and among these, acetic anhydride and vinyl acetate are preferred from the viewpoint of reaction efficiency.

Each step of the method of this embodiment is described below.

<Dehydration process>
The method of the present embodiment may include a dehydration step prior to the modification step. In the dehydration step, the cellulose-containing pulp and/or the aprotic polar solvent are dehydrated to obtain a slurry with an adjusted moisture content. The dehydration may be performed using the pulp and/or the aprotic polar solvent alone or in a mixed state. The moisture content may be adjusted by one or a combination of two or more selected from the group consisting of temperature control (e.g., heating with an oven), pressure control (e.g., reducing pressure with a pressure reducer), humidity control (e.g., dehumidification with a dehumidifier), and use of a dehydrating agent (e.g., use of an adsorbent solid dehydrating agent such as zeolite or molecular sieves).

In the dehydration step, the moisture content of the raw pulp, the aprotic polar solvent, the modifier, the catalyst, and/or the slurry containing these is preferably adjusted to 5% by mass or less, or 3% by mass or less, or 1% by mass or less. Although a lower moisture content is preferable, in one embodiment, from the viewpoint of process efficiency, it may be 0.6% by mass or more, or 0.7% by mass or more, or 0.8% by mass or more.

<Modification step>
In this process, the raw pulp is chemically modified to the inside of the fiber in a slurry containing raw pulp, an aprotic polar solvent, a modifier, and a catalyst to obtain a chemically modified pulp. In general, the value of the degree of substitution DS of a fibrous material reflects the degree of substitution DS near the surface of the fibrous material. Therefore, the degree of substitution DS of the chemically modified fine cellulose fiber, which is a defibrated product of raw pulp that has not been chemically modified to the inside of the fiber, is smaller than the degree of substitution DS of the raw pulp. In the present disclosure, an indicator that the pulp has been chemically modified to the inside of the fiber is that ΔDS, which is the difference between the degree of substitution DS of the chemically modified pulp and the degree of substitution DS of the chemically modified fine cellulose fiber, is less than 0.3. ΔDS is preferably 0.25 or less, or 0.20 or less, or 0.18 or less, or 0.17 or less, or 0.16 or less, or 0.15 or less. The smaller ΔDS is the more desirable, but from the viewpoint of ease of production of the chemically modified fine cellulose fibers, in one embodiment, ΔDS may be 0.01 or more, 0.03 or more, or 0.05 or more.

Water in the slurry may be a factor that hinders the desired modification reaction of the hydroxyl groups of cellulose in the modification process. For example, when the chemical modification is esterification, the hydroxyl groups react with an esterifying agent to produce ester groups and water. Since this reaction is an equilibrium reaction, the presence of water in the system inhibits the progress of esterification. In the method of this embodiment, the moisture content of the slurry is maintained, in one embodiment, less than 6% by mass, or 3% by mass or less, or 1% by mass or less throughout the modification process. By maintaining the slurry at a moisture content below a specific value, the modification reaction proceeds well, and the pulp can be chemically modified to the inside of the fibers. The lower the moisture content of the slurry, the more desirable it is, but from the viewpoint of ease of process management, in one embodiment, it may be 0.6% by mass or more, 0.7% by mass or more, or 0.8% by mass or more.

The means for controlling the moisture content in the slurry include, but are not limited to,
By carrying out the dehydration step, the moisture content of the slurry to be subjected to the modification step is adjusted to a desired range;
The modification step is carried out in an inert atmosphere such as a nitrogen atmosphere;
carrying out the modification step under reduced pressure;
When the modification step is carried out in an inert atmosphere or under reduced pressure, the moisture content of the slurry can be maintained throughout the modification step at or below the moisture content at the start of the modification step.
Since the raw pulp is essentially hydrophilic and therefore tends to have a high moisture content, it is particularly useful to dehydrate the raw pulp in the above-mentioned dewatering step.

In one embodiment, the moisture content of the aprotic polar solvent is adjusted to 1% by mass or less in the dehydration process, and the moisture content of the slurry is 1% by mass or less throughout the modification process.

Without being bound by theory, it is believed that the modification process of this embodiment allows the aprotic polar solvent to increase the interfibril distance of cellulose, thereby allowing the modifier to penetrate into the inside of the pulp, and thus the pulp can be chemically modified to the inside of the fibers. In one aspect, when the degree of substitution DS of the chemically modified pulp, which will be described later, is 0.8 or more, it is clear that the raw pulp has been chemically modified to the inside of the fibers.

The interfibril distance of the raw pulp in the slurry subjected to the modification process is preferably 10 nm or more, or 11 nm or more, or 12 nm or more, from the viewpoint of enabling the pulp to be chemically modified to the inside of the fiber, and is preferably 50 nm or less, or 40 nm or less, or 30 nm or less, from the viewpoint of maintaining the inherent good mechanical properties of cellulose.
The interfibril distance is a value measured by small angle X-ray scattering [SAXS].

The interfibril distance can be controlled by adjusting one or more of the following: the type of raw pulp and/or aprotic polar solvent, the mass ratio of raw pulp to aprotic polar solvent in the slurry, the concentration of the aprotic polar solvent in the medium, etc.

In one embodiment, the pulp can maintain its shape before and after the modification process. Here, "the pulp maintains its shape" means that there is no defibration during the modification process, and the fiber diameter after modification is the same as before modification (in one embodiment, the rate of change in average fiber width before and after chemical modification is 20% or less). Such chemical modification allows the desired chemically modified fine cellulose fibers to be obtained in high yield.

In terms of the production efficiency of chemically modified pulp, particularly from the viewpoint of reducing the amount of solvent used in the mass production process, the raw material pulp content in the slurry is, in one embodiment, 4% by mass or more, or 8% by mass or more, or 10% by mass or more. From the viewpoint of the production efficiency of chemically modified pulp, the higher the raw material pulp content, the more desirable it is, but from the viewpoint of improving the fluidity of the slurry, in one embodiment, the raw material pulp content is 25% by mass or less, or 20% by mass or less, or 15% by mass or less.

In one embodiment, the aprotic polar solvent content in the slurry is 96% by mass or less, or 95% by mass or less, or 92% by mass or less, or 90% by mass or less, and in one embodiment, 65% by mass or more, or 69% by mass or more, or 70% by mass or more, or 74% by mass or more, or 75% by mass or more, or 79% by mass or more, or 80% by mass or more.

The modifier addition rate in the slurry can be adjusted as appropriate depending on the type of modifier, but in one embodiment, it is 50 parts by mass or more, or 53 parts by mass or more, or 55 parts by mass or more, or 60 parts by mass or more, or 64 parts by mass or more, or 65 parts by mass or more, or 70 parts by mass or more, or 75 parts by mass or more, or 80 parts by mass or more, and in one embodiment, it is 160 parts by mass or less, or 159 parts by mass or less, or 155 parts by mass or less, or 150 parts by mass or less, or 145 parts by mass or less, or 140 parts by mass or less, or 135 parts by mass or less, or 133 parts by mass or less, or 130 parts by mass or less, or 125 parts by mass or less, or 120 parts by mass or less, or 115 parts by mass or less, or 110 parts by mass or less, or 106 parts by mass or less, relative to 100 parts by mass of pulp.

<Filtration preparation process (floc formation)>
The method of the present embodiment may include a filtration preparation step after the modification step and before the filtration step. The filtration preparation step is a step of flocculating (i.e. aggregating) the chemically modified pulp in the slurry by adding a flocculant to the slurry after the modification step. After flocculation, the solid content may be increased by deliquification. Flocculating the chemically modified pulp is advantageous from the viewpoint of improving the drainage of the slurry in the subsequent filtration step. The filtration preparation step obtains a slurry having a flocculant content of preferably 50% by mass or less, or 45 parts by mass or less, or 40% by mass or less.

As the flocculant, a protic solvent, i.e., a solvent having a hydrogen bond donor group, is preferred from the viewpoint of facilitating purification of the chemically modified pulp in the filtration process. Examples of protic solvents include alcohols such as methanol, ethanol, isopropanol, isobutanol, and t-butanol, polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin, and water, among which water is preferred because of its high solubility parameter (SP value). Without being bound by theory, it is believed that when a protic solvent is added to chemically modified pulp, the catalyst is ionized and salted out, and the hydrophobic groups of the modifier aggregate to cause flocculation, thereby improving the freeness in the filtration process.

From the viewpoint of good flocculation, the amount of flocculant added is preferably 5 parts by mass or more, or 10 parts by mass or more, or 15 parts by mass or more, and preferably 50 parts by mass or less, or 40 parts by mass or less, per 100 parts by mass of the slurry after the modification process.

In this step, in order to make the flocculation proceed more smoothly, additional components may be used as necessary in addition to the flocculating agent. Examples of additional components include surfactants such as carboxylates, sulfonates, and sulfate ester salts; inorganic salts such as aluminum sulfate, ferric chloride, ferrous sulfate, calcium chloride, and sodium chloride; and the like. The amount of any additional component used is appropriately selected as desired, but may be, for example, 0.01 to 30% by mass relative to the total amount of the slurry at the time of flocculation (100% by mass).

The slurry after flocculation can be deliquified (i.e., concentrated) using methods such as suction filtration, pressure filtration, and centrifugal deliquification. From the viewpoint of maintaining the formed flocs, suction filtration or pressure filtration is preferred as the deliquification method. The solid content of the slurry after deliquification is preferably 5% by mass or more, or 10% by mass or more, or 15% by mass or more, and preferably 30% by mass or less, or 25% by mass or less, or 20% by mass or less.

<Filtration process>
The method of the present embodiment may include a filtration step after the modification step. In one aspect, a filtration preparation step and a filtration step may be performed after the modification step. The slurry can be purified by filtering the slurry to obtain a chemically modified pulp of high purity. In the filtration step, it is preferable to add a purification solvent to the slurry and then perform filtration. As the purification solvent, a protic solvent is preferable, and examples of the purification solvent include alcohols such as methanol, ethanol, isopropanol, isobutanol, and t-butanol, polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin, and water, and among these, water is preferable.

In one embodiment, the catalyst in the slurry may be removed by filtration, and the catalyst concentration in the slurry obtained in the filtration step is preferably 1% by mass or less, or 0.6% by mass or less, or 0.4% by mass or less. Although it is desirable for the catalyst concentration to be low, in one embodiment, from the viewpoint of process efficiency, it may be 0.1% by mass or more, or 0.2% by mass or more, or 0.3% by mass or more. In a preferred embodiment, the catalyst is an inorganic salt, and the catalyst concentration in the slurry obtained in the filtration step is 1% by mass or less.
In this manner, chemically modified pulp can be produced.

<Defibrillation process>
In this step, the chemically modified pulp is defibrated (i.e., refined) to obtain chemically modified fine cellulose fibers. This refinement process may be carried out using a single device once or more, or may be carried out using multiple devices once or more.
The device used for the micronization is not particularly limited, but for example, a high-pressure or ultra-high-pressure homogenizer, refiner, beater, PFI mill, kneader, disperser, high-speed fiberizer, grinder (stone-type grinder), ball mill, vibration mill, bead mill, conical refiner, disk-type refiner, single-axis, twin-axis or multi-axis kneader/extruder, etc. can be used.

In one embodiment, chemically modified fine cellulose fibers can be prepared by dispersing chemically modified pulp in water and/or other media (e.g., organic solvents, inorganic acids, bases and/or ionic liquids) and micronizing the pulp by a micronization process.

The total amount of water and/or other medium used in the micronization process is not particularly limited as long as it is an effective amount capable of dispersing the chemically modified pulp, but is preferably at least 1 time by mass, or at least 10 times by mass, or at least 50 times by mass, and is preferably no more than 10,000 times by mass, or no more than 5,000 times by mass, or no more than 2,000 times by mass, or no more than 1,000 times by mass, relative to the chemically modified pulp.

A dried product can be prepared by drying the chemically modified fine cellulose fiber slurry, in which the chemically modified fine cellulose fibers are dispersed in a liquid, under controlled drying conditions. Dryers include, but are not limited to, kneaders, planetary mixers, Henschel mixers, high-speed mixers, propeller mixers, ribbon mixers, single- or twin-screw extruders, Banbury mixers, freeze dryers, shelf dryers, spray dryers, fluidized bed dryers, etc.

As the liquid medium for the chemically modified fine cellulose fiber slurry, water and/or other media (for example, organic solvents, inorganic acids, bases and/or ionic liquids) can be suitably used.
The concentration of the chemically modified fine cellulose fibers in the chemically modified fine cellulose fiber slurry is preferably 1% by mass or more, or 2% by mass or more, or 3% by mass or more, or 5% by mass or more, or 10% by mass or more, or 15% by mass or more, or 20% by mass or more, or 25% by mass or more from the viewpoint of process efficiency during drying, and is preferably 60% by mass or less, or 55% by mass or less, or 50% by mass or less, or 45% by mass or less, or 40% by mass or less, or 35% by mass or less from the viewpoint of avoiding an excessive increase in the viscosity of the slurry and solidification due to aggregation and maintaining good handleability. For example, the production of chemically modified fine cellulose fibers is often carried out in a dilute dispersion, and the concentration of the chemically modified fine cellulose fibers in the slurry may be adjusted to the preferred range by concentrating such a dilute dispersion. For concentration, methods such as suction filtration, pressure filtration, centrifugal deliquation, and heating can be used.
Components other than the chemically modified fine cellulose fibers, such as a dispersant, may be added before, during, and/or after drying of the chemically modified fine cellulose fiber slurry. The mode of addition of the dispersant is not particularly limited.

<Characteristics of raw pulp, chemically modified pulp, or chemically modified fine cellulose fiber>
[Average fiber diameter and average fiber length of raw pulp or chemically modified pulp]
The raw pulp or chemically modified pulp has an average fiber diameter of more than 1 μm, and is therefore a coarse fiber. In one embodiment, the average fiber diameter is more than 1 μm, or 10 μm or more, or 20 μm or more, and in one embodiment, 100 μm or less, or 80 μm or less, or 60 μm or less.

The average fiber length of the raw pulp or chemically modified pulp is, in one embodiment, 500 μm or more, and in another embodiment, 5 mm or less, or 4 mm or less, or 3 mm or less.

The average fiber diameter and average fiber length of raw pulp or chemically modified pulp are values measured using a Molfi-Neo fiber analyzer.

[Polymorphism]
Known crystalline polymorphs of cellulose include types I, II, III, and IV, of which types I and II are particularly widely used, and types III and IV have been obtained on a laboratory scale but are not widely used on an industrial scale. If the crystalline polymorphism of the raw pulp is type I or type II, the mechanical properties (strength, dimensional stability) of the resulting chemically modified fine cellulose fibers are high, and the strength and dimensional stability of the resin composition when the chemically modified fine cellulose fibers are dispersed in a resin are high, which is preferable.

[Crystallization degree of raw pulp, chemically modified pulp, or chemically modified cellulose fiber]
The crystallinity of the raw material pulp is preferably 50% or more. When the crystallinity is in this range, the mechanical properties (strength, dimensional stability) of the cellulose itself are high, so that when the chemically modified fine cellulose fibers are dispersed in a resin, the strength and dimensional stability of the resin composition tend to be high. A more preferable lower limit of the crystallinity is 55% or more, or 60% or more, or 65% or more, or 70% or more, or 75% or more, and most preferably 80% or more. There is no particular upper limit for the crystallinity of the raw material pulp, and the higher the better, but from the viewpoint of production, the preferable upper limit is 99%.

The crystallinity of the chemically modified pulp or chemically modified fine cellulose fibers is preferably 55% or more, or 60% or more, or 70% or more, or 80% or more, from the viewpoint of obtaining a resin composition having excellent heat resistance, mechanical strength, and dimensional stability. When the crystallinity is within this range, the mechanical properties (heat resistance, strength, dimensional stability) of the cellulose itself are high, so that when the cellulose is dispersed in the resin, the heat resistance, strength, and dimensional stability of the resin composition tend to be high. A higher crystallinity is preferable, but from the viewpoint of production, the upper limit is preferably 99%.

In the present disclosure, when the cellulose in a sample is cellulose type I crystals (derived from natural cellulose), the crystallinity is determined by the Segal method from the diffraction pattern (2θ/deg. is 10 to 30) obtained by measuring the sample by wide-angle X-ray diffraction, according to the following formula.
Crystallinity (%) = [I ₍₂₀₀₎ - I _(amorphous) ] / I ₍₂₀₀₎ x 100
I ₍₂₀₀₎ : Diffraction peak intensity due to the 200 plane (2θ = 22.5°) in cellulose I type crystals I _(amorphous) : A halo peak intensity due to amorphous in cellulose I type crystals, which is a peak intensity at an angle 4.5° lower than the diffraction angle of the 200 plane (2θ = 18.0°)

When the cellulose in the sample is cellulose II type crystals, the degree of crystallinity can be calculated from the absolute peak intensity h0 at 2θ=12.6° assigned to the (110) plane peak of cellulose II type crystals in wide-angle X-ray diffraction and the peak intensity h1 of the baseline (the line connecting 2θ=8° and 15°) at this interplanar spacing, according to the following formula:
Crystallinity (%) = (h0-h1) /h0 ×100

[Porous sheet]
In addition, the values of the crystal polymorphism, crystallinity, degree of polymerization, Mw, Mn, Mw/Mn, average content of alkali-soluble polysaccharides, average content of acid-insoluble components, T _D , T _1% , T _{250° C.} , DS, DSs, DS heterogeneity ratio, and coefficient of variation of DS heterogeneity ratio of the present disclosure may vary greatly depending on the form of the measurement sample. In order to perform stable and reproducible measurements, a porous sheet without distortion is used as the measurement sample. The method for producing the porous sheet is as follows.

First, a concentrated cake of a sample with a solid content of 10% by mass or more is added to tert-butanol, and a dispersion process is performed using a mixer or the like until no aggregates are present. The concentration is adjusted to 0.5% by mass for 0.5 g of sample solid content weight. 100 g of the obtained tert-butanol dispersion is filtered on filter paper. The filtered material is not peeled off from the filter paper, but is sandwiched between two sheets of larger filter paper together with the filter paper, and the edges of the larger filter paper are pressed down with a weight and dried in an oven at 150 ° C. for 5 minutes. The filter paper is then peeled off to obtain a porous sheet with little distortion. The sheet with an air resistance R of 100 sec/100 ml or less per 10 g/ ^m2 of sheet basis weight is used as a porous sheet and is used as a measurement sample.
The air resistance R is measured by measuring the basis weight W (g/ ^m2 ) of a porous sheet sample left to stand for one day in an environment of 23°C and 50% RH, and then measuring the air resistance R (sec/100 ml) using an Oken air resistance tester (manufactured by Asahi Seiko Co., Ltd., model EG01). At this time, the value per basis weight of 10 g/ ^m2 is calculated according to the following formula.
Air resistance per unit area of 10 g/ ^m2 (sec/100 ml) = R/W x 10

[Degree of polymerization of raw pulp, chemically modified pulp, or chemically modified cellulose fiber]
The degree of polymerization of the raw pulp, chemically modified pulp or chemically modified fine cellulose fibers is preferably 100 or more, or 150 or more, or 200 or more, or 300 or more, or 400 or more, or 450 or more, and preferably 3500 or less, or 3300 or less, or 3200 or less, or 3100 or less, or 3000 or less.

From the viewpoint of processability and mechanical property expression, it is desirable to set the degree of polymerization within the above-mentioned range. From the viewpoint of processability, it is preferable that the degree of polymerization is not too high, and from the viewpoint of mechanical property expression, it is desirable that the degree of polymerization is not too low.

The degree of polymerization in this disclosure refers to the average degree of polymerization measured according to the reduced specific viscosity method using a copper ethylenediamine solution described in Verification Test (3) of the "Japanese Pharmacopoeia 15th Edition Commentary (published by Hirokawa Shoten)."

[Mw/Mn]
In one embodiment, the weight average molecular weight (Mw) of the raw pulp, chemically modified pulp or chemically modified fine cellulose fiber is preferably 100,000 or more, or 120,000 or more, or 150,000 or more, or 180,000 or more, or 200,000 or more. The ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight (Mn) is preferably 6 or less, or 5.6 or less, or 5.4 or less. The larger the weight average molecular weight, the fewer the number of terminal groups of the cellulose molecule. In addition, since the ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight represents the width of the molecular weight distribution, the smaller the Mw/Mn, the fewer the number of terminals of the cellulose molecule. Since the terminals of the cellulose molecules are the starting points of thermal decomposition, not only when the weight average molecular weight is large but also when the width of the molecular weight distribution is narrow at the same time, a particularly high heat resistant fine cellulose fiber and a resin composition containing the fine cellulose fiber and the resin can be obtained. The weight average molecular weight (Mw) may be, for example, 600,000 or less, or 500,000 or less, or 400,000 or less, from the viewpoint of the availability of the cellulose fiber raw material. The ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight (Mn) may be, for example, 1.5 or more, or 1.7 or more, or 2 or more, from the viewpoint of the ease of production of the raw pulp, chemically modified pulp, or chemically modified fine cellulose fiber. Mw can be controlled to the above range by selecting a cellulose fiber raw material having an Mw according to the purpose, appropriately performing physical treatment and/or chemical treatment on the cellulose fiber raw material in an appropriate range, etc. Mw/Mn can also be controlled to the above range by selecting a cellulose fiber raw material having an Mw/Mn according to the purpose, appropriately performing physical treatment and/or chemical treatment on the cellulose fiber raw material in an appropriate range, etc. In both the control of Mw and the control of Mw/Mn, examples of the physical treatment include physical treatments that apply mechanical forces such as dry or wet grinding using a microfluidizer, ball mill, disk mill, etc., and impact, shear, friction, etc. using a crusher, homomixer, high-pressure homogenizer, ultrasonic device, etc., and examples of the chemical treatments include digestion, bleaching, acid treatment, enzyme treatment, conversion to regenerated cellulose, hydrolysis treatment, etc.

The weight average molecular weight and number average molecular weight referred to here are values obtained by dissolving a sample in N,N-dimethylacetamide containing added lithium chloride, and then performing gel permeation chromatography using N,N-dimethylacetamide as a solvent.

[Average alkali-soluble content of raw pulp, chemically modified pulp, or chemically modified fine cellulose fiber]
Alkali-soluble polysaccharides such as hemicellulose and acid-insoluble components such as lignin are present between the microfibrils and between the microfibril bundles of raw pulp, chemically modified pulp, or chemically modified fine cellulose fibers. Hemicellulose is a polysaccharide composed of sugars such as mannan and xylan, and plays a role in binding the microfibrils together by hydrogen bonding with cellulose. Lignin is a compound having an aromatic ring, and is known to be covalently bonded to hemicellulose in the cell walls of plants.

The alkali-soluble polysaccharides that may be contained in raw pulp, chemically modified pulp, or chemically modified fine cellulose fibers include hemicellulose, as well as β-cellulose and γ-cellulose. Those skilled in the art will understand alkali-soluble polysaccharides as components obtained as the alkali-soluble portion of holocellulose obtained by solvent extraction and chlorine treatment of plants (e.g., wood) (i.e., components obtained by removing α-cellulose from holocellulose).

In one embodiment, the average content of alkali-soluble polysaccharides in the raw pulp, chemically modified pulp, or chemically modified fine cellulose fiber is preferably 20% by mass or less, 18% by mass or less, 15% by mass or less, or 12% by mass or less, based on 100% by mass of the raw pulp, chemically modified pulp, or chemically modified fine cellulose fiber, from the viewpoint of maintaining the mechanical strength of the chemically modified fine cellulose fiber during melt kneading and suppressing yellowing. From the viewpoint of the availability of the raw pulp, the above content may be 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 2% by mass or more, or 3% by mass or more.

The average alkali-soluble polysaccharide content can be determined by the method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000), by subtracting the α-cellulose content from the holocellulose content (Wise method). This method is understood in the industry as a method for measuring the amount of hemicellulose. The alkali-soluble polysaccharide content is calculated three times for each sample, and the number average of the calculated alkali-soluble polysaccharide contents is taken as the average alkali-soluble polysaccharide content.

[Average content of acid insoluble components in raw pulp, chemically modified pulp, or chemically modified fine cellulose fiber]
The acid-insoluble components that may be contained in raw pulp, chemically modified pulp, or chemically modified fine cellulose fibers are understood by those skilled in the art as insoluble components remaining after a defatted sample obtained by solvent extraction of a plant (e.g., wood) is treated with sulfuric acid. The acid-insoluble components are specifically, but not limited to, lignin derived from aromatic compounds.

In one aspect, the average content of acid-insoluble components in the raw pulp, chemically modified pulp, or chemically modified fine cellulose fiber is preferably 10% by mass or less, 5% by mass or less, or 3% by mass or less, based on 100% by mass of the raw pulp, chemically modified pulp, or chemically modified fine cellulose fiber, from the viewpoint of avoiding a decrease in heat resistance of the fine cellulose fiber and the associated discoloration. From the viewpoint of the ease of availability of the raw pulp, the above content may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more.

The average acid-insoluble content is determined by quantifying the acid-insoluble content using the Clason method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000). This method is understood in the industry as a method for measuring the amount of lignin. The sample is stirred in a sulfuric acid solution to dissolve cellulose, hemicellulose, etc., and then filtered through a glass fiber filter. The resulting residue corresponds to the acid-insoluble components. The acid-insoluble component content is calculated from the weight of the acid-insoluble components, and the number average of the acid-insoluble component contents calculated for the three samples is taken as the average acid-insoluble component content.

[Number average fiber diameter and L/D ratio of chemically modified fine cellulose fibers]
In one aspect, the number average fiber diameter of the chemically modified fine cellulose fibers is preferably 2 to 1000 nm from the viewpoint of obtaining a good effect of improving physical properties by the chemically modified fine cellulose fibers. The number average fiber diameter of the chemically modified fine cellulose fibers is more preferably 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more, and more preferably 900 nm or less, or 800 nm or less, or 700 nm or less, or 600 nm or less, or 500 nm or less, or 400 nm or less, or 300 nm or less, or 200 nm or less.

The number average fiber length (L)/number average fiber diameter (D) ratio of the chemically modified fine cellulose fibers is preferably 30 or more, or 50 or more, or 80 or more, or 100 or more, or 120 or more, or 150 or more, from the viewpoint of effectively improving the mechanical properties of a resin composition containing the chemically modified fine cellulose fibers with a small amount of the chemically modified fine cellulose fibers. The upper limit is not particularly limited, but is preferably 5000 or less, or 3000 or less, or 2000 or less, or 1000 or less, from the viewpoint of handleability.

In one embodiment, the number average fiber diameter (D), number average fiber length (L), and L/D ratio of the chemically modified fine cellulose fibers of the present disclosure are values measured using a scanning electron microscope (SEM) according to the following procedure. An aqueous dispersion of chemically modified fine cellulose fibers is replaced with tert-butanol, diluted to 0.001 to 0.1% by mass, and dispersed using a high-shear homogenizer (e.g., manufactured by IKA, product name "Ultra Turrax T18") under processing conditions: rotation speed 15,000 rpm x 3 minutes. The sample is cast on an osmium-deposited silicon substrate and air-dried to obtain a measurement sample, which is measured using a high-resolution scanning electron microscope (SEM). Specifically, the length (L) and diameter (D) of 100 randomly selected fibrous substances are measured in an observation field where the magnification is adjusted so that at least 100 fibrous substances are observed, and the ratio (L/D) is calculated. For cellulose fibers, the number average length (L), number average diameter (D), and number average ratio (L/D) are calculated.

[Degree of substitution (DS) of chemically modified pulp]
From the viewpoint of obtaining good dispersibility of the chemically modified fine cellulose fiber in a resin and good heat resistance (i.e., high thermal decomposition onset temperature), the degree of substitution (DS) of the chemically modified pulp is, in one embodiment, 0.3 or more, or 0.4 or more, or 0.5 or more, or 0.6 or more, or 0.8 or more. The degree of substitution (DS) may be 3.0 in one embodiment, but from the viewpoint of obtaining chemically modified fine cellulose fiber having good mechanical properties inherent to cellulose (particularly tensile strength, dimensional stability, etc.), in one embodiment, it is 2.0 or less, or 1.9 or less, or 1.8 or less, or 1.5 or less, or 1.2 or less.

[Degree of substitution (DS) of chemically modified fine cellulose fiber]
From the viewpoint of obtaining chemically modified fine cellulose fibers having excellent dispersibility in resins, heat resistance, etc., the degree of chemical modification (DS) of the chemically modified fine cellulose fibers is, in one embodiment, 0.3 or more, or 0.4 or more, or 0.5 or more, or 0.6 or more, or 0.7 or more, or 0.8 or more; from the viewpoint of obtaining chemically modified fine cellulose fibers having good mechanical properties inherent to cellulose, the degree of chemical modification (DS) is, in one embodiment, 1.8 or less, or 1.5 or less, or 1.2 or less, or 1.1 or less, or 1.0 or less.

[DSs/DSt of chemically modified fine cellulose fiber]
The DS heterogeneity ratio (DSs/DSt), defined as the ratio of the degree of modification (DSs) of the fiber surface to the degree of modification (DSt) of the entire fiber of the chemically modified fine cellulose fiber (which is synonymous with the above-mentioned degree of substitution (DS)), is preferably 1.05 or more. The larger the value of the DS heterogeneity ratio, the more pronounced the heterogeneous structure of the sheath-core structure (i.e., the fiber surface layer is highly chemically modified while the fiber center maintains the structure of cellulose close to the original unmodified cellulose structure), and while having high tensile strength and dimensional stability derived from cellulose, it is possible to improve the affinity with the resin when composited with the resin and improve the dimensional stability of the resin composition. The DS heterogeneity ratio is more preferably 1.1 or more, or 1.2 or more, or 1.3 or more, or 1.5 or more, or 2.0 or more, and from the viewpoint of ease of production of the chemically modified fine cellulose fiber, it is preferably 30 or less, or 20 or less, or 10 or less, or 6 or less, or 4 or less, or 3 or less.

The value of DSs varies depending on the degree of substitution of the chemically modified fine cellulose fiber, but as an example, it is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, even more preferably 0.5 or more, and preferably 3.0 or less, more preferably 2.5 or less, particularly preferably 2.0 or less, even more preferably 1.5 or less, especially preferably 1.2 or less, and most preferably 1.0 or less. The preferred range of DSt is as described above for the substituent (DS).

The smaller the coefficient of variation (CV) of the DS heterogeneity ratio of the chemically modified fine cellulose fiber, the smaller the variation in various physical properties of the resin composition, and therefore the more preferable. The coefficient of variation is preferably 50% or less, or 40% or less, or 30% or less, or 20% or less. The coefficient of variation can be further reduced, for example, by a method in which the cellulose fiber raw material is defibrated and then chemically modified to obtain chemically modified fine cellulose fiber (i.e., a sequential method), whereas it can be increased by a method in which the defibration and chemical modification of the cellulose fiber raw material are performed simultaneously (i.e., a simultaneous method). Although the mechanism of this action is not clear, in the simultaneous method, chemical modification is more likely to proceed in the thin fibers generated in the early stages of defibration, and it is believed that defibration proceeds further when the hydrogen bonds between the cellulose microfibrils are reduced by chemical modification, resulting in an increase in the coefficient of variation of the DS heterogeneity ratio.

[Measurement of Degree of Substitution (DS)]
The degree of substitution (DS) of the chemically modified pulp or chemically modified fine cellulose fiber, which is an esterified product, can be measured by the following method. The degree of substitution (DS) can be calculated based on the peak intensity ratio of the peak derived from the acyl group and the peak derived from the cellulose skeleton from the reflection infrared absorption spectrum of the esterified pulp or esterified fine cellulose fiber. The peak of the absorption band of C=O based on the acyl group appears at 1730 cm ^-1 , and the peak of the absorption band of C-O based on the cellulose skeleton appears at 1030 cm ^-1 . The DS of the esterified pulp or esterified fine cellulose fiber is obtained by preparing a correlation graph between the DS obtained from the solid-state NMR measurement of the esterified pulp or esterified fine cellulose fiber described later and the modification ratio (IR index 1030) defined as the ratio of the peak intensity of the absorption band of C=O based on the acyl group to the peak intensity of the absorption band of C-O of the cellulose skeleton chain, and calculating the calibration curve substitution degree DS = 4.13 × IR index (1030) from the correlation graph.
It can be found by using

The DS of the esterified pulp or esterified fine cellulose fiber by solid-state NMR can be calculated by carrying out ^13C solid-state NMR measurement on the frozen and pulverized esterified pulp or esterified fine cellulose fiber, and calculating the DS from the total area intensity (Inp) of the signals assigned to the carbon atoms C1 to C6 derived from the pyranose ring of cellulose appearing in the range of 50 ppm to 110 ppm, relative to the area intensity (Inf) of the signal assigned to one carbon atom derived from the modifying group, according to the following formula:
DS=(Inf)×6/(Inp)
For example, when the modifying group is an acetyl group, the signal at 23 ppm assigned to _--CH3 may be used.
The conditions for the ¹³ C solid state NMR measurement are, for example, as follows.
Equipment: Bruker Biospin Avance500WB
Frequency: 125.77MHz
Measurement method: DD/MAS method Waiting time: 75 sec
NMR sample tube: 4 mm diameter
Accumulation times: 640 times (approximately 14 hours)
MAS: 14,500Hz
Chemical shift reference: glycine (external reference: 176.03 ppm)

[Evaluation of DS heterogeneity ratio]
The coefficient of variation (CV) of the DS heterogeneity ratio is calculated by taking 100 g of an aqueous dispersion of chemically modified fine cellulose fiber (solid content of 10 mass% or more), freeze-pulverizing 10 g each to prepare measurement samples, calculating the DS heterogeneity ratio from the DSt and DSs of the 10 samples, and then using the standard deviation (σ) and arithmetic mean (μ) of the DS heterogeneity ratio among the obtained 10 samples, using the following formula.
DS heterogeneity ratio = DSs / DSt
Coefficient of variation (%) = standard deviation σ/arithmetic mean μ × 100

The DSs is calculated as follows. That is, the porous sheet is measured by X-ray photoelectron spectroscopy (XPS). The XPS spectrum reflects the constituent elements and chemical bond state of only the surface layer of the sample (typically about a few nm). Peak separation is performed on the obtained C1s spectrum, and the DSs can be calculated by the following formula from the area intensity (Ixf) of the peak attributable to one carbon atom derived from the modifying group relative to the area intensity (Ixp) of the peak attributable to carbons C2-C6 derived from the pyranose ring of cellulose (289 eV, C-C bond).
DSs=(Ixf)×5/(Ixp)
For example, when the modifying group is an acetyl group, the C1s spectrum is subjected to peak separation at 285 eV, 286 eV, 288 eV, and 289 eV, and then the peak at 289 eV is used as Ixp, and the peak (286 eV) derived from the O—C═O bond of the acetyl group is used as Ixf.
The conditions for the XPS measurement are, for example, as follows:
Equipment used: ULVAC-Phi VersaProbe II
Excitation source: mono. AlKα 15 kV x 3.33 mA
Analysis size: Approximately 200 μm φ
Photoelectron extraction angle: 45°
Capture area Narrow scan: C 1s, O 1s
Pass Energy: 23.5eV

[Thermal decomposition temperature of chemically modified fine cellulose fibers]
From the viewpoint of avoiding thermal degradation during melt-kneading and exhibiting mechanical strength, the thermal decomposition onset temperature (T _D ) of the chemically modified fine cellulose fiber is preferably 220° C. or higher, or 230° C. or higher, or 240° C. or higher, or 250° C. or higher, or 260° C. or higher, or 270° C. or higher, or 275° C. or higher, or 280° C. or higher, or 285° C. or higher in one embodiment. The higher the thermal decomposition onset temperature, the more preferable it is, but from the viewpoint of ease of production of the fine cellulose fiber, it may be, for example, 320° C. or lower, 310° C. or lower, or 300° C. or lower.

From the viewpoint of avoiding thermal degradation during melt-kneading and exhibiting mechanical strength, the temperature at which the chemically modified fine cellulose fiber loses 1 wt% weight (T1 _% ) is preferably 230° C. or more, or 240° C. or more, or 250° C. or more, or 260° C. or more, or 270° C. or more, or 275° C. or more, or 280° C. or more, or 285° C. or more, or 290° C. or more in one embodiment. The higher _T1% is, the more preferable, but from the viewpoint of ease of production of the fine cellulose fiber, it may be, for example, 330° C. or less, 320° C. or less, or 310° C. or less.

From the viewpoint of avoiding thermal degradation during melt kneading and exhibiting mechanical strength, the 250°C weight loss rate (T250 _°C ) of the chemically modified fine cellulose fiber is preferably 15% or less, or 12% or less, or 10% or less, or 8% or less, or 6% or less, or 5% or less, or 4% or less, or 3% or less in one embodiment. The lower _{the T250°C} , the more preferable it is, but from the viewpoint of ease of production of the fine cellulose fiber, it may be, for example, 0.1% or more, or 0.5% or more, or 0.7% or more, or 1.0% or more.

In the present disclosure, T _D is a value obtained from a graph in which the horizontal axis is temperature and the vertical axis is weight residual percentage in a thermogravimetric (TG) analysis under nitrogen flow. Chemically modified fine cellulose fiber is heated from room temperature to 150°C at a heating rate of 10°C/min in a nitrogen flow of 100 ml/min, and then held at 150°C for 1 hour, and then heated to 450°C at a heating rate of 10°C/min. Starting from the weight (weight loss of 0 wt%) at 150°C (a state in which moisture is almost removed), a straight line is obtained that passes through the temperature at 1 wt% weight loss (T _1% ) and the temperature at 2 wt% weight loss (T _2% ). The temperature at the point where this straight line intersects with a horizontal line (baseline) that passes through the starting point of the weight loss of 0 wt% is defined as T _D.

The 1% weight loss temperature (T _1% ) is the temperature at which a 1% weight loss occurs from a weight of 150° C. as a starting point when the temperature is continued to be increased by the above-mentioned _TD method.

The 250°C weight loss rate ( _T250°C ) of the chemically modified fine cellulose fiber is the weight loss rate when the chemically modified fine cellulose fiber is held at 250°C under nitrogen flow for 2 hours in TG analysis. The chemically modified fine cellulose fiber is heated from room temperature to 150°C at a heating rate of 10°C/min in a nitrogen flow of 100 ml/min, held at 150°C for 1 hour, then heated from 150°C to 250°C at a heating rate of 10°C/min, and held at 250°C for 2 hours. The weight W0 at the time when 250°C is reached is taken as the starting point, and the weight after holding at 250°C for 2 hours is taken as W1, and is calculated from the following formula.
Weight change rate at 250°C (%): (W1-W0)/W0 x 100

The degree of polymerization, Mw, Mn, Mw/Mn, average acid-insoluble content, etc. of chemically modified pulp may be regarded as the values of the chemically modified pulp immediately before chemical modification.

In a preferred embodiment, the raw material pulp has an average fiber length of 500 μm or more and an average fiber diameter of 20 μm or more, and has the following characteristics (1) to (4):
(1) Crystallinity of 50% or more,
(2) a weight average molecular weight (Mw) of 100,000 or more, and a weight average molecular weight (Mw)/number average molecular weight (Mn) ratio of 6 or less,
(3) average acid-insoluble component content of 10% by mass or less, and (4) average alkali-soluble polysaccharide content of 12% by mass or less,
One or more of the following conditions is satisfied:

In a preferred embodiment, the chemical modification is esterification using a carboxylic acid vinyl ester as an esterifying agent;
The degree of substitution (DS) of the chemically modified pulp is 2.0 or less;
The degree of substitution (DS) of the chemically modified fine cellulose fiber is 0.8 to 1.8;
The coefficient of variation (CV) of the DS non-uniformity ratio of the chemically modified fine cellulose fiber is 20% or less.

[Evaluation of the properties of chemically modified fine cellulose fibers in resin]
Various physical properties of the chemically modified fine cellulose fibers in the resin composition (more specifically, number average fiber length, number average fiber diameter, L/D ratio, crystallinity, crystalline polymorphism, degree of polymerization, Mw, Mn, Mw/Mn, average content of alkali-soluble polysaccharides, average content of acid-insoluble components, T _D , T _1% , T _{250° C.} , DS, DSs, DS heterogeneity ratio, and coefficient of variation of DS heterogeneity ratio) are analyzed by the following method. The resin components in the resin composition are dissolved in an organic or inorganic solvent capable of dissolving the resin components of the resin composition, the chemically modified fine cellulose fibers are separated, and the fibers are thoroughly washed with the solvent, and the solvent is replaced with tert-butanol. Thereafter, the tert-butanol slurry of the chemically modified fine cellulose fibers is analyzed using the same measurement method as the above-mentioned method, and various physical properties of the chemically modified fine cellulose fibers in the resin composition are calculated.

<Method for producing resin composition>
Another aspect of the present invention provides a method for producing a resin composition containing chemically modified fine cellulose fibers and a resin.

The amount of chemically modified fine cellulose fibers relative to 100% by mass of the entire resin composition is preferably 0.1% by mass or more, or 0.5% by mass or more, or 1% by mass or more, or 3% by mass or more, from the viewpoint of obtaining a good reinforcing effect by the chemically modified fine cellulose fibers, and is preferably 30% by mass or less, or 25% by mass or less, or 20% by mass or less, or 15% by mass or less, from the viewpoint of maintaining the inherent properties of the resin well.

The amount of resin relative to 100% by mass of the entire resin composition is preferably 20% by mass or more, or 30% by mass or more, or 40% by mass or more, or 50% by mass or more, or 60% by mass or more, or 70% by mass or more, or 75% by mass or more, or 80% by mass or more, or 85% by mass or more, from the viewpoint of maintaining the inherent properties of the resin well, and is preferably 99.9% by mass or less, or 99.5% by mass or less, or 99% by mass or less, or 97% by mass or less, or 95% by mass or less, or 90% by mass or less, from the viewpoint of obtaining the effects of other components well.

<Resin>
Examples of the resin include thermoplastic resins, curable resins, rubber-based resins, etc., and resin precursors can also be blended in. Such resins or resin precursors can be used alone or in combination of two or more.
In an exemplary embodiment, the resin is a thermoplastic resin.

The thermoplastic resin may be, for example, a crystalline resin having a melting point in the range of 100°C to 350°C, an amorphous resin having a glass transition temperature in the range of 100 to 250°C, etc. In this disclosure, the melting point refers to the peak top temperature of the endothermic peak that appears when the temperature is increased from 23°C at a heating rate of 10°C/min using a differential scanning calorimeter (DSC), and when two or more endothermic peaks appear, it refers to the peak top temperature of the endothermic peak on the highest temperature side. The enthalpy of the endothermic peak at this time is preferably 10 J/g or more, more preferably 20 J/g or more. In addition, when measuring, it is preferable to use a sample that is once heated to a temperature condition of melting point + 20°C or more, melts the resin, and then cooled to 23°C at a heating rate of 10°C/min. In this disclosure, the glass transition temperature refers to the peak top temperature at which the storage modulus drops significantly and the loss modulus becomes maximum when measured using a dynamic viscoelasticity measuring device at a heating rate of 2°C/min from 23°C and an applied frequency of 10 Hz. When two or more loss modulus peaks appear, the glass transition temperature refers to the peak top temperature of the highest temperature peak. In this case, the measurement frequency is preferably at least once every 30 seconds to improve measurement accuracy. There are no particular restrictions on the method of preparing the measurement sample, but from the viewpoint of eliminating the influence of molding distortion, it is preferable to use a cut piece of a heat press molded product, and from the viewpoint of thermal conduction, it is preferable that the size (width and thickness) of the cut piece is as small as possible.

Examples of crystalline resins include polyolefin resins, polyamide resins, polyester resins, polyacetal resins, polyphenylene sulfide resins, polyether ether ketone resins, polyimide resins, liquid crystal polymers, and polytetrafluoroethylene resins. Examples of mixtures of two or more of these resins include polyolefin resins, polyamide resins, polyester resins, and polyacetal resins from the viewpoints of handling and cost, and polyamide resins, polyolefin resins, and polyacetal resins are more preferable. From the viewpoint of increasing the heat resistance of the resin composition, the melting point of the crystalline resin is preferably 140°C or higher, or 150°C or higher, or 160°C or higher, or 170°C or higher, or 180°C or higher, or 190°C or higher, or 200°C or higher, or 210°C or higher, or 220°C or higher, or 230°C or higher, or 240°C or higher, or 245°C or higher, or 250°C or higher.

Examples of amorphous resins include amorphous polyolefin resins such as polymethylene pentene and cyclic polyolefin, amorphous polyvinyl resins such as polystyrene and polyvinyl chloride, polycarbonate resins, acrylic resins, methacrylic resins, polyvinyl alcohol resins, polysulfone resins, polyphenylene ether resins, polyethersulfone resins, acrylonitrile-styrene resins, acrylonitrile-butadiene-styrene resins, polyketone resins, polyetherimide resins, and polyamideimide resins.

From the viewpoint of increasing the heat resistance of the resin composition, the molding temperature of the amorphous resin is preferably 130°C or more, 140°C or more, or 150°C or more, or 160°C or more, or 170°C or more, or 180°C or more, or 190°C or more, or 200°C or more, or 210°C or more, or 220°C or more, or 230°C or more, or 240°C or more, or 245°C or more, or 250°C or more.

[Polyolefin resin]
The polyolefin resin preferred as the thermoplastic resin is a polymer obtained by polymerizing olefins (e.g., α-olefins) and/or alkenes as monomer units. Specific examples of the polyolefin resin include ethylene (co)polymers exemplified by low-density polyethylene (e.g., linear low-density polyethylene), high-density polyethylene, ultra-low-density polyethylene, and ultra-high-molecular-weight polyethylene, polypropylene (co)polymers exemplified by polypropylene, ethylene-propylene copolymer, and ethylene-propylene-diene copolymer, and copolymers of ethylene and α-olefins exemplified by ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer, and ethylene-glycidyl methacrylate copolymer.

Here, the most preferred polyolefin resin is polypropylene. In particular, polypropylene having a melt mass flow rate (MFR) of 3 g/10 min or more and 50 g/10 min or less, measured at 230° C. and a load of 21.2 N in accordance with ISO 1133, is preferred. The lower limit of MFR is more preferably 5 g/10 min, 6 g/10 min, or 8 g/10 min. The upper limit is more preferably 40 g/10 min, 30 g/10 min, 25 g/10 min, 20 g/10 min, or 18 g/10 min. It is desirable that the MFR does not exceed the upper limit from the viewpoint of improving the toughness of the resin composition, and it is desirable that the MFR does not exceed the lower limit from the viewpoint of the fluidity of the resin composition.

In addition, in order to increase the affinity with the chemically modified fine cellulose fibers, an acid-modified polyolefin resin can also be suitably used. As the acid used for the acid modification, a mono- or polycarboxylic acid can be used, and examples thereof include maleic acid, fumaric acid, succinic acid, phthalic acid and their anhydrides, and citric acid. Maleic acid or its anhydride is particularly preferred because it is easy to increase the modification rate. There is no particular restriction on the modification method, but a method in which a polyolefin resin is heated to above its melting point in the presence or absence of a peroxide and melt-kneaded is common. As the polyolefin resin to be acid-modified, all of the above-mentioned polyolefin resins can be used, but polypropylene is particularly suitable. The acid-modified polypropylene resin may be used alone, but it is more preferable to use it in combination with an unmodified polypropylene resin in order to adjust the modification rate of the resin as a whole. In this case, the ratio of the acid-modified polypropylene resin to all polypropylene resins is preferably 0.5% by mass to 50% by mass. A more preferred lower limit is 1% by mass, or 2% by mass, or 3% by mass, or 4% by mass, or 5% by mass. A more preferred upper limit is 45% by mass, or 40% by mass, or 35% by mass, or 30% by mass, or 20% by mass. In order to maintain the interfacial strength between the resin and the chemically modified fine cellulose fiber, a content equal to or greater than the lower limit is preferred, and in order to maintain the ductility of the resin, a content equal to or less than the upper limit is preferred.

The melt mass flow rate (MFR) of the acid-modified polypropylene resin, measured in accordance with ISO1133 at 230°C and a load of 21.2 N, is preferably 50 g/10 min or more, 100 g/10 min or more, 150 g/10 min or more, or 200 g/10 min or more, from the viewpoint of increasing the affinity at the interface between the resin and the chemically modified fine cellulose fiber. There is no particular upper limit, but it is preferably 500 g/10 min in order to maintain mechanical strength.

[Polyamide resin]
Examples of polyamide-based resins that are preferable as the thermoplastic resin include polyamides obtained by polycondensation reaction of lactams (e.g., polyamide 6, polyamide 11, polyamide 12, etc.); diamines (e.g., 1,6-hexanediamine, 2-methyl-1,5-pentanediamine, 1,7-heptanediamine, 2-methyl-1-6-hexanediamine, 1,8-octanediamine, 2-methyl-1,7-heptanediamine, 1,9-nonanediamine, 2-methyl-1,8-octanediamine, 1,10-decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine, m-xylylenediamine, etc.) and dicarboxylic acids (e.g., butanedioic acid, pentanedioic acid, hexanedioic acid, , heptanedioic acid, octanedioic acid, nonanedioic acid, decanedioic acid, benzene-1,2-dicarboxylic acid, benzene-1,3-dicarboxylic acid, benzene-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid, cyclohexane-1,4-dicarboxylic acid, etc.) (for example, polyamide 6,6, polyamide 6,10, polyamide 6,11, polyamide 6,12, polyamide 6,T, polyamide 6,I, polyamide 9,T, polyamide 10,T, polyamide 2M5,T, polyamide MXD,6, polyamide 6,C, polyamide 2M5,C, etc.); and copolymers in which these are copolymerized, respectively (for example, polyamide 6,T/6,I, etc.).

Among these polyamide resins, aliphatic polyamides such as polyamide 6, polyamide 11, polyamide 12, polyamide 6,6, polyamide 6,10, polyamide 6,11, and polyamide 6,12, and alicyclic polyamides such as polyamide 6,C and polyamide 2M5,C are more preferred.

From the viewpoint of improving the heat resistance of the resin composition, the melting point of the polyamide resin is preferably 220°C or higher, or 230°C or higher, or 240°C or higher, or 245°C or higher, or 250°C or higher, and from the viewpoint of ease of manufacture of the resin composition, the melting point is preferably 350°C or lower, or 320°C or lower, or 300°C or lower.

There is no particular restriction on the terminal carboxyl group concentration of the polyamide resin, but it is preferably 20 μmol/g or more, or 30 μmol/g or more, and preferably 150 μmol/g or less, or 100 μmol/g or less, or 80 μmol/g or less.

In the polyamide resin, the ratio of carboxyl end groups to all end groups ([COOH]/[total end groups]) is preferably 0.30 or more, or 0.35 or more, or 0.40 or more, or 0.45 or more from the viewpoint of dispersibility of the chemically modified fine cellulose fiber in the resin composition, and is preferably 0.95 or less, or 0.90 or less, or 0.85 or less, or 0.80 or less from the viewpoint of the color tone of the resin composition.

The end group concentration of polyamide resins can be adjusted by known methods. One adjustment method is to add a terminal regulator (e.g., diamine compounds, monoamine compounds, dicarboxylic acid compounds, monocarboxylic acid compounds, acid anhydrides, monoisocyanates, monoacid halides, monoesters, monoalcohols, etc.) that reacts with the end groups during polymerization of polyamide to the polymerization liquid so as to achieve a predetermined end group concentration.

Examples of terminal regulators that react with terminal amino groups include aliphatic monocarboxylic acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearic acid, pivalic acid, and isobutyric acid; alicyclic monocarboxylic acids such as cyclohexanecarboxylic acid; aromatic monocarboxylic acids such as benzoic acid, toluic acid, α-naphthalenecarboxylic acid, β-naphthalenecarboxylic acid, methylnaphthalenecarboxylic acid, and phenylacetic acid; and mixtures of a plurality of terminal regulators selected from the group consisting of acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearic acid, and benzoic acid, and acetic acid is the most preferred, from the standpoints of reactivity, stability of the blocked terminal, and price.

Examples of terminal regulators that react with terminal carboxyl groups include aliphatic monoamines such as methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, decylamine, stearylamine, dimethylamine, diethylamine, dipropylamine, and dibutylamine; alicyclic monoamines such as cyclohexylamine and dicyclohexylamine; aromatic monoamines such as aniline, toluidine, diphenylamine, and naphthylamine, and any mixtures thereof. Among these, one or more terminal regulators selected from the group consisting of butylamine, hexylamine, octylamine, decylamine, stearylamine, cyclohexylamine, and aniline are preferred in terms of reactivity, boiling point, stability of the blocked terminals, price, and the like.

The concentrations of amino end groups and carboxyl end groups of a polyamide resin can be determined from the integrated values of characteristic signals corresponding to each end group by ¹ H-NMR. This method is preferred in terms of accuracy and simplicity. More specifically, it is recommended to use the method described in JP-A-7-228775, use deuterated trifluoroacetic acid as the measurement solvent, and set the number of integration scans to 300 or more.

The intrinsic viscosity [η] of a polyamide resin measured in concentrated sulfuric acid at 30°C is preferably 0.6 to 2.0 dL/g, or 0.7 to 1.4 dL/g, or 0.7 to 1.2 dL/g, or 0.7 to 1.0 dL/g, from the viewpoint of good in-mold fluidity and good appearance of molded pieces when the resin composition is, for example, injection molded. In this disclosure, "intrinsic viscosity" is synonymous with the viscosity generally called limiting viscosity. The intrinsic viscosity is determined by measuring the ηsp/c of several measurement solvents with different concentrations in 96% concentrated sulfuric acid at a temperature of 30°C, deriving the relationship between each of the ηsp/c and the concentration (c), and extrapolating the concentration to zero. This value extrapolated to zero is the intrinsic viscosity. Details of the above method are described, for example, in Polymer Process Engineering (Prentice-Hall, Inc. 1994), pages 291 to 294. From the viewpoint of accuracy, it is desirable to set the concentrations in the above-mentioned measurement solvents having different concentrations to at least four points (e.g., 0.05 g/dL, 0.1 g/dL, 0.2 g/dL, 0.4 g/dL).

[Polyester resin]
As a polyester-based resin preferable as the thermoplastic resin, one or more selected from polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), polyhydroxyalkanoic acid (PHA), polylactic acid (PLA), polyarylate (PAR), etc. can be used. Among them, PET, PBS, PBSA, PBT and PEN are more preferable, and PBS, PBSA and PBT are particularly preferable.

The terminal groups of the polyester resin can be changed as desired by the monomer ratio during polymerization, the presence or absence and amount of addition of a terminal stabilizer, etc. The ratio of carboxyl terminal groups to all terminal groups of the polyester resin ([COOH]/[total terminal groups]) is preferably 0.30 or more, or 0.35 or more, or 0.40 or more, or 0.45 or more from the viewpoint of dispersibility of the chemically modified fine cellulose fiber in the resin composition, and is preferably 0.95 or less, or 0.90 or less, or 0.85 or less, or 0.80 or less from the viewpoint of the color tone of the resin composition.

[Polyacetal resin]
Polyacetal resins preferred as thermoplastic resins are generally homopolyacetals made from formaldehyde and copolyacetals containing trioxane as a main monomer and 1,3-dioxolane as a comonomer component, and although both can be used, copolyacetals are preferred from the viewpoint of thermal stability during processing. The amount of the structure derived from the comonomer component (e.g., 1,3-dioxolane) is preferably 0.01 mol% or more, or 0.05 mol% or more, or 0.1 mol% or more, or 0.2 mol% or more from the viewpoint of thermal stability during extrusion processing and molding processing, and is preferably 4.0 mol% or less, or 3.5 mol% or less, or 3.0 mol% or less, or 2.5 mol% or less, or 2.3 mol% or less from the viewpoint of mechanical strength.

[Additional Ingredients]
The resin composition may further contain additional components as necessary to improve its performance. Examples of the additional components include filler components other than cellulose; compatibilizers; plasticizers; polysaccharides such as starches and alginic acid; natural proteins such as gelatin, glue, and casein; inorganic compounds such as zeolite, ceramics, talc, silica, metal oxides, and metal powders; colorants; fragrances; pigments; flow regulators; leveling agents; conductive agents; antioxidants; antistatic agents; ultraviolet absorbers; ultraviolet dispersants; and deodorants. The content ratio of any additional component in the resin composition is appropriately selected within a range in which the desired effects of the present invention are not impaired, and may be, for example, 0.01 to 50% by mass, or 0.1 to 30% by mass.

As the dispersant, a compound capable of reacting with or forming a hydrogen bond with the hydroxyl group of cellulose is preferred. Suitable examples of the dispersant include one or more selected from the group consisting of cellulose derivatives, polyalkylene oxides, amides, and amines. Among them, cellulose derivatives are preferred because they have a high affinity with cellulose since they are cellulose-based substances, while they are also thermoplastic resins, and therefore have a high effect of improving the dispersion stability of cellulose in the resin composition. As the dispersant, one having a boiling point higher than that of water is preferred. Note that a boiling point higher than that of water refers to a boiling point higher than the boiling point of water at each pressure on the vapor pressure curve (for example, 100°C at 1 atmosphere).

In the resin composition, the amount of dispersant per 100 parts by mass of chemically modified fine cellulose fiber is preferably 1 part by mass or more, or 5 parts by mass or more, or 10 parts by mass or more, or 20 parts by mass or more from the viewpoint of good dispersion of cellulose and network formation, and is preferably 500 parts by mass or less, or 300 parts by mass or less, or 200 parts by mass or less from the viewpoint of reducing variation in performance of the resin composition.
An example of a process for manufacturing an article will be described.

[Method 1]
In one embodiment of the method for producing a resin composition,
In the fiberization step in the method for producing chemically modified fine cellulose fibers of the present disclosure, the chemically modified pulp and resin are mixed and the chemically modified pulp is fiberized to produce a resin composition containing the chemically modified fine cellulose fibers and the resin.

In the above method, the chemically modified pulp can be defibrated together with the resin by mixing means such as a mixing roller, kneader, Banbury mixer, or extruder. When the resin is a thermoplastic resin, the mixing may be melt kneading.

When the resin is a thermoplastic resin, a preferred process condition for the fiber defibration and mixing step is to provide a zone with a blocking effect midway through the twin-screw extrusion. This zone is composed of elements that function to block or reverse the mixture of chemically modified pulp and thermoplastic resin, and typically includes a seal disk, reverse flight, reverse kneading disk element, etc.

[Method 2]
In another embodiment, a method for producing a resin composition includes the steps of:
A fiber forming step of producing chemically modified fine cellulose fibers by the method for producing chemically modified fine cellulose fibers of the present disclosure; and a mixing step of mixing the chemically modified fine cellulose fibers with a resin to produce a resin composition.
including.

In the mixing step, the chemically modified fine cellulose fibers may be mixed with the resin in the form of a dry body or a slurry (e.g., a water dispersion). When the resin is a thermoplastic resin, the mixing may be melt-kneading. The heating temperature during melt-kneading can be adjusted according to the resin used, and is preferably a temperature that is equal to or higher than the melting point of the resin but does not significantly exceed the melting point. The heating temperature is preferably equal to or higher than the melting point of the resin, or equal to or higher than the melting point + 20°C, or equal to or higher than the melting point + 30°C, or equal to or higher than the melting point + 40°C, and from the viewpoint of suppressing thermal deterioration of the resin composition, it is preferably equal to or lower than the melting point + 90°C, or equal to or lower than the melting point + 80°C, or equal to or lower than the melting point + 70°C. The above melting point means the melting point on the highest temperature side when the resin composition contains multiple types of thermoplastic resins. The minimum processing temperatures recommended by thermoplastic resin suppliers are 255-270°C for nylon 66, 225-240°C for nylon 6, 170°C-190°C for polyacetal resin, and 160-180°C for polypropylene. The heating setting temperature may be in the range of 20°C higher than these recommended minimum processing temperatures.

The moisture content of the mixture subjected to melt kneading is preferably 0.2% by mass or less, or 0.1% by mass or less, or 0.07% by mass or less. From the viewpoint of ease of process control, the moisture content may be, for example, 0.001% by mass or more.

For melt kneading, an extruder such as a single screw extruder or a twin screw extruder can be used, but a twin screw extruder is preferred in terms of controlling the dispersibility of the cellulose. The L/D ratio, obtained by dividing the cylinder length (L) of the extruder by the screw diameter (D), is preferably 40 or more, and particularly preferably 50 or more. The screw rotation speed during kneading is preferably in the range of 100 to 800 rpm, and more preferably in the range of 150 to 600 rpm. These values vary depending on the screw design.

Weak kneading (i.e., kneading under small shear force) is preferable from the viewpoint of suppressing thermal degradation of the resin composition. Weak kneading can be achieved, for example, by providing many conveying zones in the screw configuration of the extruder and by reducing the number of rotations of the screw. Each screw in the cylinder of the extruder is optimized by combining a full-flight screw with an elliptical two-blade screw shape, a kneading element called a kneading disk, and the like.

<Shape of resin composition>
The resin composition of this embodiment can be provided in various shapes. Specifically, resin pellets, sheets, fibers, plates, rods, etc. can be mentioned, but the resin pellet shape is preferred from the viewpoint of ease of post-processing and ease of transportation. Preferred resin pellet shapes include round, elliptical, and cylindrical shapes, and the shape may vary depending on the cutting method used during extrusion processing. For example, pellets cut by a cutting method called underwater cutting are often round, pellets cut by a cutting method called hot cutting are often round or elliptical, and pellets cut by a cutting method called strand cutting are often cylindrical. The preferred pellet diameter of round pellets is 1 mm or more and 3 mm or less. The preferred diameter of cylindrical pellets is 1 mm or more and 3 mm or less, and the preferred length is 2 mm or more and 10 mm or less. It is desirable to set the above diameter and length to be equal to or greater than the lower limit from the viewpoint of operational stability during extrusion, and it is desirable to set them to be equal to or less than the upper limit from the viewpoint of bite into the molding machine during post-processing.

The resin composition of this embodiment can be used as various resin molded bodies. There are no particular limitations on the method for producing the resin molded body, but injection molding, extrusion molding, blow molding, inflation molding, foam molding, and the like can be used. Of these, injection molding is particularly preferred from the standpoint of design and cost.

<Applications of resin composition>
The resin composition obtained by the method of the present embodiment is useful as a substitute for steel plates, fiber-reinforced plastics (e.g., carbon fiber-reinforced plastics, glass fiber-reinforced plastics, etc.), resin composites containing inorganic fillers, etc. Suitable applications of the resin composition include industrial machine parts, general machine parts, automobile/railroad/vehicle/ship/aerospace-related parts, electronic/electrical parts, building/civil engineering materials, daily necessities, sports/leisure goods, housing parts for wind power generation, container/packaging parts, etc.

The following provides further explanation of exemplary aspects of the present invention using examples, but the present invention is not limited to the following examples.

<Study on moisture absorption behavior of raw pulp and solvent>
The moisture absorption of various cellulose-based materials at a relative humidity of 100% was measured. The sheet-like raw materials were cut into 1-2 cm squares and measured using a heat-drying moisture meter MX-50 manufactured by A&D Co., Ltd. The results are shown in Table 1.

The linter pulp was also chopped into 1 cm cubes and dried using a dryer (Yamato DKG610), after which it was allowed to absorb moisture at 20°C and a relative humidity of 50% and the change in moisture content over time was evaluated. The results are shown in Table 2.

In addition, dimethyl sulfoxide (DMSO) was dried using a molecular sieve, and then the moisture content was evaluated over time when it was allowed to absorb moisture at 20°C and a relative humidity of 50%. The results are shown in Table 3.

Table 4 also shows the moisture content of slurries with various solid content when the moisture content in the raw pulp and the aprotic polar solvent is changed.

The above results show that both raw pulp and dimethyl sulfoxide (DMSO) absorb moisture in the air. In the chemical modification of raw pulp, the modifying agent is consumed by the moisture in the system, so the modification reaction is delayed roughly in proportion to the amount of moisture. Based on the above results, we investigated the appropriate amount of moisture in the slurry to ensure sufficient interfibril distance and allow the chemical modification to proceed smoothly to the inside of the pulp.

Evaluation method
<Moisture content>
A Karl Fischer moisture meter (Kyoto Electronics Manufacturing Co., Ltd., "MKC-710M") was used as the measuring device, and "Kem-Aqua Anolyte AGE" and "Kem-Aqua Catholyte CGE" both manufactured by Kyoto Electronics Manufacturing Co., Ltd. were used as the electrode solutions.

<Degree of substitution (DS)>
[Preparation of porous sheet]
First, the concentrated cake was added to tert-butanol, and further dispersed in a mixer or the like until no aggregates were present. The concentration was adjusted to 0.5% by mass relative to 0.5 g of fine cellulose fiber solids. 100 g of the obtained tert-butanol dispersion was filtered on filter paper. The filtered material was not peeled off from the filter paper, but was sandwiched between two sheets of larger filter paper together with the filter paper, and the edges of the larger filter paper were pressed down with a weight and dried for 5 minutes in an oven at 150 ° C. Then, the filter paper was peeled off to obtain a porous sheet with little distortion. The sheet with an air resistance of 100 sec/100 ml or less per 10 g/ ^m2 sheet basis weight was used as a porous sheet and was used as a measurement sample.
After measuring the basis weight W (g/ ^m2 ) of the sample left to stand for one day in an environment of 23°C and 50% RH, the air resistance R (sec/100 ml) was measured using an Oken type air resistance tester (manufactured by Asahi Seiko Co., Ltd., model EG01). At this time, the value per basis weight of 10 g/ ^m2 was calculated according to the following formula.
Air resistance per unit area of 10 g/ ^m2 (sec/100 ml) = R/W x 10

[Degree of substitution (DS)]
The infrared spectrum of the porous sheet at five points was measured by an ATR-IR method using a Fourier transform infrared spectrophotometer (FT/IR-6200 manufactured by JASCO Corp.) The infrared spectrum measurement was performed under the following conditions.
Number of times: 64
Wavenumber resolution: 4cm ^-1 ,
Measurement wave number range: 4000 to 600 cm ^-1 ,
ATR crystal: Diamond,
Incident angle: 45°

From the obtained IR spectrum, the IR index was calculated according to the following formula:
IR index = H1730/H1030
In the formula, H1730 and H1030 are the absorbances at 1730 cm ^-1 and 1030 cm ^-1 (absorption bands of C-O stretching vibration of the cellulose backbone chain). However, the lines connecting 1900 cm ^-1 and 1500 cm ^-1 and the line connecting 800 cm ^-1 and 1500 cm ^-1 are taken as baselines, and the absorbances are calculated based on these baselines as 0 absorbance.
The average degree of substitution at each measurement site was calculated from the IR index according to the following formula, and the average value was taken as DS.
DS = 4.13 x IR index

<Difference in DS before and after defibration (ΔDS)>
For the chemically modified pulp and chemically modified fine cellulose fibers of each Example and Comparative Example, the DS was measured using the above-mentioned IR DS measurement method, and the difference between the DS before defibration, which is the DS of the chemically modified pulp, and the DS after defibration, which is the DS of the chemically modified fine cellulose fibers, was defined as ΔDS.

<Coefficient of variation of DS heterogeneity ratio>
100 g of an aqueous dispersion of chemically modified fine cellulose fiber (solid content of 10% by mass or more) was collected, and 10 g of each was freeze-pulverized to prepare measurement samples. The DS heterogeneity ratio was calculated from the DSt and DSs of the 10 samples, and then the standard deviation (σ) and arithmetic mean (μ) of the DS heterogeneity ratios among the obtained 10 samples were used to calculate the DS heterogeneity ratio according to the following formula.
DS heterogeneity ratio = DSs / DSt
Coefficient of variation (%) = standard deviation σ/arithmetic mean μ × 100

The calculation method of DSs is as follows. That is, the porous sheet was measured by X-ray photoelectron spectroscopy (XPS). The XPS spectrum reflects the constituent elements and chemical bond state of only the surface layer of the sample (typically about a few nm). Peak separation was performed on the obtained C1s spectrum, and the DSs was calculated by the following formula from the area intensity (Ixf) of the peak attributable to one carbon atom derived from the modifying group relative to the area intensity (Ixp) of the peak attributable to carbons C2-C6 derived from the pyranose ring of cellulose (289 eV, C-C bond).
DSs=(Ixf)×5/(Ixp)
Specifically, after peak separation of the C1s spectrum at 285 eV, 286 eV, 288 eV, and 289 eV, the peak at 289 eV was used for Ixp, and the peak (286 eV) derived from the O—C═O bond of the acetyl group was used for Ixf.
The conditions used for the XPS measurement are as follows:
Equipment used: ULVAC-Phi VersaProbe II
Excitation source: mono. AlKα 15 kV x 3.33 mA
Analysis size: Approximately 200 μm φ
Photoelectron extraction angle: 45°
Capture area Narrow scan: C 1s, O 1s
Pass Energy: 23.5eV

<Time to reach DS=1>
In the modification step, the time until DS became 1 or more by IR measurement was measured.

<Fiber diameter and fiber length of raw pulp and chemically modified pulp>
Pure water was added to the raw pulp or the slurry after the modification step to adjust the solid content to 30 mg/L, and then the fiber diameter and fiber length were measured using a laboratory fiber analyzer Morfi-Neo manufactured by Techpap.

<Crystallization degree of raw pulp>
The porous sheet was subjected to X-ray diffraction measurement, and the crystallinity was calculated from the following formula.
Crystallinity (%) = [I ₍₂₀₀₎ - I _(amorphous) ] / I ₍₂₀₀₎ x 100
I ₍₂₀₀₎ : Diffraction peak intensity due to the 200 plane (2θ = 22.5°) in cellulose I type crystals I _(amorphous) : A halo peak intensity due to amorphous in cellulose I type crystals, which is a peak intensity at an angle 4.5° lower than the diffraction angle of the 200 plane (2θ = 18.0°) (X-ray diffraction measurement conditions)
Device: MiniFlex (manufactured by Rigaku Corporation)
Operation axis 2θ/θ
Radiation source: CuKα
Measurement method: Continuous Voltage: 40 kV
Current: 15mA
Starting angle 2θ=5°
End angle 2θ = 30°
Sampling width 0.020°
Scan speed: 2.0°/min
Sample: A porous sheet is attached onto the sample holder.

<Mw and Mw/Mn of raw pulp>
0.88 g of the porous sheet was weighed, cut into small pieces with scissors, lightly stirred, and then 20 mL of pure water was added and left for one day. Next, water and solids were separated by centrifugation. Then, 20 mL of acetone was added, lightly stirred, and left for one day. Next, acetone and solids were separated by centrifugation. Then, 20 mL of N,N-dimethylacetamide was added, lightly stirred, and left for one day. N,N-dimethylacetamide and solids were separated again by centrifugation, and then 20 mL of N,N-dimethylacetamide was added, lightly stirred, and left for one day. N,N-dimethylacetamide and solids were separated by centrifugation, and 19.2 g of N,N-dimethylacetamide solution prepared so that lithium chloride was 8 mass percent was added to the solids, and the mixture was stirred with a stirrer, and it was confirmed that it was dissolved by visual observation. The solution in which the cellulose nanofibers were dissolved was filtered through a 0.45 μm filter, and the filtrate was used as a sample for gel permeation chromatography. The apparatus and measurement conditions used are as follows.
Equipment: Tosoh Corporation HLC-8120
Column: TSKgel SuperAWM-H (6.0 mm ID x 15 cm) x 2 Detector: RI detector Eluent: N,N-dimethylacetamide (lithium chloride 0.2%)
Flow rate: 0.6 mL/min. Calibration curve: Pullulan equivalent

<Average content of acid insoluble matter in raw pulp>
The acid-insoluble components were quantified by the Clason method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pages 92-97, 2000). The completely dried raw pulp was precisely weighed, placed in a specified container, and 72% by mass of concentrated sulfuric acid was added. The contents were appropriately pressed with a glass rod so as to make the contents uniform, and then autoclaved to dissolve the cellulose and hemicellulose in the acid solution. After cooling, the contents were filtered with glass fiber filter paper, and the acid-insoluble components were obtained as a residue. The acid-insoluble component content was calculated from the weight of the acid-insoluble components, and the number average of the acid-insoluble component contents calculated for the three samples was taken as the average acid-insoluble component content.

<Average content of alkali-soluble components in raw pulp>
The average alkali-soluble polysaccharide content was determined by subtracting the α-cellulose content from the holocellulose content (Wise method) according to the method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000). The alkali-soluble polysaccharide content was calculated three times for each sample, and the number average of the calculated alkali-soluble polysaccharide contents was taken as the average alkali-soluble polysaccharide content of the raw material pulp.

<Fiber diameter of chemically modified fine cellulose fibers>
The fiber diameter of the fine cellulose fibers according to each of the Examples and Comparative Examples was measured using a fiber analyzer Morfi-Neo (manufactured by MorFi Compact Co., Ltd.). In addition, it was confirmed that the fiber diameter was 1 μm or less using a scanning electron microscope (SEM) (manufactured by JEOL Ltd., model number JSM-6700F).

のように円環平均することで１次元散乱プロファイルＩｏｂｓ（２θ）を得た。
Ｐ：偏光因子
２θ：散乱角
φ：方位角 <Fibril distance of raw pulp in slurry>
For the slurry at the start of the modification step, the distance between microfibrils was measured using a small angle X-ray scattering method (NANOPIX, manufactured by Rigaku Corporation) under the following conditions.
X-ray wavelength λ: 0.154nm
Optical system: Point collimation "2PHR" mode (1st: 0.55 mm, 2nd: Open, Guard: 0.35 mm)
Detector: Hypix-6000 (2D semiconductor detector)
Camera length l: 1312 mm (one measurement, z: -150 offset)
Exposure time: 15 min/sample Data processing: For the scattering pattern I (2θ, φ) measured by the circular average two-dimensional detector, the following formula (1):

A one-dimensional scattering profile Iobs(2θ) was obtained by circular averaging as follows:
P: Polarization factor 2θ: Scattering angle φ: Azimuth angle

[Scattering Intensity Correction]
The one-dimensional profile calculated by the above formula (1) includes scattering from the sample as well as scattering from the window material, air, and other sources other than the sample. The scattering intensity also depends on the instrument and sample thickness. To correct for these, empty cell scattering was performed. Film thickness correction was not performed.

[Analysis of inter-microfibril distance]
The distance between microfibrils was analyzed using the MuliPeakFit function of the analysis software Igor 8.00. Linear baseline correction was performed on the log-log plot, and fitting was performed using a Gaussian function. The fitting conditions are shown below.
Linear baseline intercept a: variable slope b: fixed Gaussian function position, width, height: variable

<Catalyst concentration after filtration process>
The slurry was measured for conductivity using a Horiba Ltd. product number D-210PC-S/D-220PC-S, and it was confirmed that the conductivity was less than 0.1 Sm ^-1 (0.01 mol/kg).

<Comprehensive evaluation of productivity of chemically modified pulp>
The time required for the DS to reach 1 and the time required for filtration (i.e., freeness) were comprehensively judged, and samples in which both were excellent were marked with an ◯, those in which one was poor were marked with a △, and those in which both were poor were marked with an ×.

<Characteristics of Resin Composition>
[Tensile yield strength]
Multipurpose test pieces in accordance with ISO294-3 were molded from the resin composition pellets using an injection molding machine, and tests were carried out under conditions in accordance with JIS K6920-2 with n = 10. When the tensile yield strength is 5 MPa or more, the physical properties are good.

[Appearance of molded piece]
The appearance of the multipurpose test piece was visually observed. Yellowish ones were rated ◯, brown ones △, and brown ones close to blackish ones ×.

[Surface smoothness]
The appearance of the multipurpose test piece was visually observed, and a mark of ◯ was given to a surface where no irregularities were observed, a mark of △ was given to a surface where irregularities were observed but the number of such irregularities was less than 30 across both sides of the test piece, and a mark of × was given to a surface where irregularities were observed but the number of such irregularities was 30 or more across both sides of the test piece.

[Composite Overall Judgment]
The tensile yield strength and appearance of the molded pieces were evaluated comprehensively, and excellent ones were rated as ◯, and poor ones as x.

Materials used:
<Resin>
Polyamide 6 (hereinafter referred to simply as PA6)
UBE nylon 1013B (manufactured by Ube Industries, Ltd.)

<Raw pulp>
Cotton linter pulp A pulp sheet obtained from Japan Pulp and Paper Co., Ltd. was used as is.
The various properties of the raw pulp were measured as follows:
Average fiber diameter: 27 μm
Average fiber length: 873 μm
Crystallinity: 79.2%
Mw: 940,000 Mw/Mn: 4.1
Average content of acid-insoluble components: 0.2% by mass
Alkali-soluble polysaccharide average content: 6.5% by mass

<Aprotic polar solvent>
Dimethyl sulfoxide (available from Gaylord)

<Production of chemically modified pulp>
<Production Example 1>
[Dehydration process]
The moisture content of the raw pulp and the aprotic polar solvent was adjusted to a target value while measuring the moisture content with a Karl Fischer moisture meter. The raw pulp was adjusted to a moisture content of 0% by mass by cutting the pulp sheet into 1 cm squares and drying it at 120°C for 2 hours in a dryer (Yamato Corporation DKG610). The aprotic polar solvent was adjusted to a moisture content of 0.013% by mass by drying it with molecular sieves.

[Modification step]
The dried dimethyl sulfoxide (30 kg) was added to a jacketed 40 L reactor, and the catalyst potassium carbonate (0.32 kg) and the dried raw pulp (2.0 kg) were added and stirred. Warm water was run through the jacket to heat the slurry to 60° C. The inside of the reactor was replaced with nitrogen, and vinyl acetate (1.0 kg) was added and reacted until DS was ≧1 by IR measurement.

[Filtration preparation process]
After the reaction was completed, the sample was flocculated by adding pure water (8.0 L) as a flocculating agent to the sample. No deliquor was performed.

[Filtration process]
A filter cloth (PP9B manufactured by Nakao Filter Kogyo Co., Ltd.) was placed in a 100 L Nutsche filter (filtration area 0.2 ^m2 ) manufactured by Mitsubishi Kakoki Co., Ltd., and the flocked sample was added and pressure filtered at room temperature. Pressure filtration with pure water (50 kg) was repeated six times at room temperature, for a total of six pressure filtrations. A concentrated cake of chemically modified pulp was obtained as described above.

<Production Example 2>
The same dehydration step as in Production Example 1 was carried out.
Next, dimethyl sulfoxide (30 kg) after drying similar to that of Production Example 1 was added to a jacketed 40 L reactor, and potassium carbonate (0.32 kg) as a catalyst and dried raw pulp (2.0 kg) were added and stirred. Water was added to the obtained slurry to adjust the moisture content to 1% by mass (i.e., the moisture content of the slurry at the start of the modification step was adjusted to 1% by mass). Warm water was run through the jacket to heat the slurry to a temperature of 60°C. The inside of the reactor was replaced with nitrogen, and vinyl acetate (1.0 kg) was added and reacted until DS ≧ 1 was obtained by IR measurement.
Next, the same filtration preparation step and filtration step were carried out as in Production Example 1. As a result, a concentrated cake of chemically modified pulp was obtained.

<Production Example 3>
A concentrated cake of chemically modified pulp was obtained in the same manner as in Production Example 2, except that the moisture content of the slurry at the start of the modification step was adjusted to 5 mass %.

<Comparative Production Example 1>
A concentrated cake of chemically modified pulp was obtained in the same manner as in Production Example 2, except that the moisture content of the slurry at the start of the modification step was adjusted to 10 mass %.

<Comparative Production Example 2>
A concentrated cake of chemically modified pulp was obtained in the same manner as in Production Example 2, except that the moisture content of the slurry at the start of the modification step was adjusted to 20 mass %.

<Production Example 4>
A concentrated cake of chemically modified pulp was obtained in the same manner as in Production Example 2, except that the amount of pure water used in the flocculation was 4.0 L.

<Production Example 5>
A concentrated cake of chemically modified pulp was obtained in the same manner as in Production Example 2, except that the amount of pure water used in flocculation was 20.0 L.

<Comparative Production Example 3>
A concentrated cake of chemically modified pulp was obtained in the same manner as in Comparative Production Example 1, except that the amount of raw pulp was 1.0 kg and the amount of pure water in flocculation was 50.0 L.

<Production Example 6>
A concentrated cake of chemically modified pulp was obtained in the same manner as in Production Example 2, except that the amount of potassium carbonate used as the catalyst was 0.16 kg.

<Production Example 7>
A concentrated cake of chemically modified pulp was obtained in the same manner as in Production Example 2, except that the amount of potassium carbonate used as the catalyst was 0.24 kg.

<Production Example 8>
A concentrated cake of chemically modified pulp was obtained in the same manner as in Production Example 2, except that the amount of raw pulp was 3.0 kg.

<Comparative Production Example 4>
A concentrated cake of chemically modified pulp was obtained in the same manner as in Comparative Production Example 1, except that the amount of potassium carbonate catalyst was 0.64 kg and flocculation was not carried out.

<Production of fine cellulose fibers>
[Examples 1 to 8, Comparative Examples 1 to 4]
Chemically modified fine cellulose fibers were produced using the concentrated cakes of chemically modified pulp produced in Production Examples 1 to 8 and Comparative Production Examples 1 to 4 in the manner shown in Table 5. Pure water was added to the concentrated cake of chemically modified pulp to adjust the solid content to 1% by mass, and the chemically modified pulp was dispersed and defibrated at room temperature (23°C) using a high-shear homogenizer (manufactured by IKA, product name "Ultra Turrax T18") under processing conditions of a rotation speed of 25,000 rpm for 5 minutes. After defibration, pressure filtration was performed to obtain chemically modified fine cellulose fibers.

<Production of resin composition>
After preparing a solution in which polyamide was diluted to 10% by mass with HFIP, the mixture was stirred using a homogenizer: T18 and a generator: S18N-19G to obtain a polyamide solution. The produced chemically modified fine cellulose was added to a cake adjusted to a moisture content of 15% by mass with HFIP so that the solid content was 0.2% by mass, and after stirring, the mixture was mixed and stirred so that the chemically modified fine cellulose/polyamide was 19/81 (by mass) to obtain a seed solution. The seed solution was spread on a flat container and dried at 80 ° C. for 30 minutes using an Espec Corporation safety oven SPH-201S, and the obtained sample was pulverized with a pulverizer and vacuum dried at 80 ° C. for 48 hours using a vacuum dryer to obtain a seed sample. The above polyamide solution was added to the seed sample so that the content of chemically modified fine cellulose fiber was 12.5% by mass, and the mixture was kneaded at 250 ° C. for 5 minutes using a Leo Labs Explorer MC15 small kneader molding machine, and then molded.

The chemically modified pulp of the present disclosure and the resin composition containing the chemically modified fine cellulose fibers using the same can form molded articles with excellent appearance and physical properties, and can therefore be suitably applied to a wide range of applications, such as industrial machine parts, general machine parts, automobile, railway, vehicle, ship, and aerospace-related parts, electronic and electrical parts, building and civil engineering materials, daily necessities, sports and leisure goods, housing parts for wind power generation, containers and packaging parts, etc.

Claims (11)

a modification step in which the raw pulp is chemically modified to the inside of the fibers in a slurry containing the raw pulp, an aprotic polar solvent, a modifying agent which is an esterifying agent, and a catalyst to obtain a chemically modified pulp; and a defibration step in which the chemically modified pulp is defibrated to produce chemically modified fine cellulose fibers.
A method for producing chemically modified fine cellulose fibers, comprising:
The raw pulp has an average fiber diameter of more than 1 μm,
The solid content of the slurry is 4% by mass or more,
The method, wherein the moisture content of the slurry is less than 6% by mass throughout the modification step. Further comprising a dehydration step prior to the modification step,
2. The method according to claim 1, wherein the dewatering step is a step of adjusting the moisture content of one or more selected from the group consisting of the raw pulp, the aprotic polar solvent, the modifying agent, the catalyst, and the slurry to 1 mass% or less by one or more selected from the group consisting of temperature control, pressure control, humidity control, and use of a dewatering agent. In the dehydration step, the water content of the aprotic polar solvent is adjusted to 1% by mass or less;
The method according to claim 2 , wherein the moisture content of the slurry is 1% by mass or less throughout the modification process. The method according to claim 1, wherein the interfibril distance of the raw pulp in the slurry subjected to the modification step is 10 nm or more. The method of claim 1, wherein the aprotic polar solvent comprises at least one selected from the group consisting of ketones, esters, nitrogen-containing compounds, sulfur-containing compounds, ethers, and halogenated hydrocarbons. The raw pulp has an average fiber length of 500 μm or more and an average fiber diameter of 20 μm or more, and has the following characteristics (1) to (4):
(1) Crystallinity of 50% or more,
(2) a weight average molecular weight (Mw) of 100,000 or more, and a weight average molecular weight (Mw)/number average molecular weight (Mn) ratio of 6 or less,
(3) average acid-insoluble component content of 10% by mass or less, and (4) average alkali-soluble polysaccharide content of 12% by mass or less,
The method of claim 1 , wherein the method satisfies one or more of the following: The method further comprises a filtering step of filtering the slurry after the modifying step,
2. The method of claim 1, wherein the catalyst is an inorganic salt and the concentration of the catalyst in the slurry obtained in the filtering step is 1% by weight or less. a filtration preparation step of adding a flocculant to the slurry after the modification step, and then draining the slurry to obtain a slurry having a flocculant content of 50 mass% or less;
a filtration step of filtering the slurry obtained in the filtration preparation step;
The method of claim 1 further comprising: the esterification agent is a vinyl carboxylate;
The degree of substitution (DS) of the chemically modified pulp is 2.0 or less;
The degree of substitution (DS) of the chemically modified fine cellulose fiber is 0.8 to 1.8,
The method according to claim 1, wherein the coefficient of variation (CV) of the DS non-uniformity ratio in the chemically modified fine cellulose fiber is 20% or less. A method for producing a resin composition using the method for producing chemically modified fine cellulose fibers according to any one of claims 1 to 9,
A method for producing a resin composition, in which in the defibration step of producing the chemically modified fine cellulose fibers, the chemically modified pulp and a resin are mixed and the chemically modified pulp is defibrated to produce a resin composition containing the chemically modified fine cellulose fibers and a resin. A fiber forming step of producing chemically modified fine cellulose fibers by the method for producing chemically modified fine cellulose fibers according to any one of claims 1 to 9, and a mixing step of mixing the chemically modified fine cellulose fibers with a resin to produce a resin composition.
A method for producing a resin composition comprising the steps of: