JP7839340B2 - Cellulose fiber dried body and method for producing the same, and method for producing resin composite - Google Patents

Description

This invention relates to a dried cellulose fiber body, a method for producing the same, and a method for producing a resin composite containing cellulose fibers and a resin.

Resin materials are widely used in various fields such as automotive components, electrical and electronic components, office equipment housings, and precision parts due to their lightness and excellent processability. However, since resin alone often lacks sufficient mechanical properties and dimensional stability, composite materials of resin and various fillers are commonly used. Recently, the use of nanofibers such as cellulose nanofibers (CNF) as such fillers has been investigated. Because nanofibers, including CNF, tend to aggregate in a dry state, they are manufactured as dispersions that allow for stable dispersion. For example, when applying cellulose nanofibers to various applications, the dispersion may be dried and then dispersed in a dispersion medium, or the dry material may be redispersed in a matrix resin. However, because the aggregation of cellulose nanofibers due to hydrogen bonding between cellulose molecules is extremely strong, various methods have been proposed to suppress the aggregation of cellulose nanofibers during the drying process.

For example, Patent Document 1 describes powdered nanofibers characterized by (A) powdered nanofibers and (B) a dispersant in a solid content of 1 to 40% by weight, and having a bulk density of 90 to 200 g/L. Patent Document 2 describes a method for producing dried microfibers with a water content of 0 to 1% by mass by homogenizing cellulose nanofibers in the presence of an organic solvent, and then removing the organic solvent. Patent Document 3 describes a method for producing dried cellulose nanofiber solids, which includes drying a mixture of cellulose nanofibers and a solvent using a vacuum drying apparatus.

Japanese Patent Publication No. 2017-210596 Japanese Patent Publication No. 2012-224960 International Publication No. 2019/189318

The technologies described in Patent Documents 1 to 3 all aim to reduce aggregation of cellulose nanofibers during drying, thereby enabling good redispersion of dried cellulose nanofibers in the dispersion medium or matrix resin. However, even with these technologies, the redispersibility of dried cellulose nanofibers is insufficient. In particular, a technology has not been established that can effectively disperse cellulose nanofibers in resin even when mixed with resin while still dry. Therefore, conventional technologies have not been able to achieve a satisfactory level of improvement in the physical properties of resins by cellulose nanofibers. In addition, during mass production, the presence of aggregates that do not pass through the screen mesh poses a problem, resulting in a very high frequency of screen mesh replacement and making mass production difficult.

One aspect of the present invention aims to solve the above-mentioned problems and provide a cellulose fiber dry material that is less likely to form aggregates causing defects such as black spots when mixed with resin, reduces the frequency of screen mesh replacement during molding, thereby providing a resin composite with excellent productivity, high toughness, and superior appearance, as well as a resin composite containing the cellulose fiber dry material and a resin.

The present invention encompasses the following embodiments.
[1] A dried cellulose fiber body containing cellulose fibers, having an angle of repose of 40° to 60°, a difference angle of 10° or less, a loose bulk density of 0.01 g/ ^cm³ to 0.40 g/ ^cm³ , a dense bulk density ^of 0.1 g/cm³ to 0.55 g/ ^cm³ , and a compressibility of 20% to 40%, with a content of 50% to 90% by mass of particulate components with a particle size of 710 μm or less.
[2] The cellulose fiber dried body according to embodiment 1, wherein the content of particulate components with a particle size of more than 710 μm and less than or equal to 1000 μm is 10% by mass to 30% by mass.
[3] The cellulose fiber dried body according to embodiment 1 or 2, wherein the content of particulate components with a particle size of more than 1000 μm is 1% by mass to 10% by mass.
[4] The cellulose fiber dried body according to any one of embodiments 1 to 3, wherein the number average fiber diameter of the cellulose fibers is 2 nm to 1000 nm.
[5] A dried cellulose fiber according to any one of embodiments 1 to 4, wherein the average fiber length (L) / fiber diameter (D) ratio of the cellulose fibers is 30 to 5000.
[6] A dried cellulose fiber according to any one of the above embodiments 1 to 5, wherein the cellulose fiber has 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.
[7] The cellulose fiber dried body according to any one of embodiments 1 to 6, wherein the degree of crystallinity of the cellulose fibers is 60% or more.
[8] The cellulose fiber dried body according to any one of embodiments 1 to 7, wherein the alkali-soluble polysaccharide content of the cellulose fiber is 20% by mass or less.
[9] The cellulose fiber dried body according to any one of embodiments 1 to 8, wherein the cellulose fibers are chemically modified.
[10] The cellulose fiber dry product according to embodiment 9, wherein the chemical modification is esterification.
[11] The cellulose fiber dried body according to embodiment 10, wherein the esterification is acetylation.
[12] A dried cellulose fiber according to any one of embodiments 9 to 11, wherein the average degree of substitution (DS) of the cellulose fibers is 0.1 to 1.2.
[13] A dried cellulose fiber according to any one of embodiments 1 to 12, wherein the moisture content is 30% by mass or less.
[14] Further comprising a dispersant,
The cellulose fiber dry body according to any one of the above embodiments 1 to 13, wherein the dispersant is a compound having an HLB value of 0.1 or higher and less than 8.0, a melting point of 80°C or lower, and a number average molecular weight of 1,000 to 50,000.
[15] A method for producing a dried cellulose fiber according to any one of the above embodiments 1 to 14,
A slurry preparation step of preparing a slurry containing cellulose fibers and an aqueous medium, and a drying step of drying the slurry under conditions of a drying rate of 10%/min to 10000%/min to form a dried cellulose fiber body.
Methods that include...
[16] The method according to embodiment 15, wherein the drying step is carried out as a continuous process with a drying temperature of 20°C to 200°C and a residence time of 0.01 minutes to 10 minutes.
[17] A method for producing a resin composite comprising cellulose fibers and resin,
This includes mixing a cellulose fiber dry product described in any of the above embodiments 1 to 16 with a resin,
A method wherein the tensile elongation at break of the resin composite is 8% or more.
[18] The method according to embodiment 17, wherein the resin is a thermoplastic resin.
[19] The method according to embodiment 18, wherein the thermoplastic resin is a polyamide resin.

According to one aspect of the present invention, a cellulose fiber dry body is provided that, when mixed with a resin, is less likely to form aggregates that cause defects such as black spots, reduces the frequency of screen mesh replacement during molding, resulting in excellent productivity, high toughness, and superior appearance. A resin composite containing the cellulose fiber dry body and a resin is also provided.

This is an explanatory diagram of the calculation methods for IR Index 1730 and IR Index 1030. This is an explanatory diagram of the measurement method for the thermal decomposition initiation temperature ( _TD ) and the 1% weight loss temperature (T1 _% ).

The following describes specific exemplary embodiments of the present invention, but the present invention is not limited to these embodiments.

≪Cellulose fiber dried material≫
One aspect of the present invention provides a cellulose fiber dry material which may be in particulate form. In the cellulose fiber dry material according to this aspect, the particle size, angle of repose, collapse angle, difference angle, loose bulk density, compacted bulk density, and degree of compressibility are controlled within a specific range. In such a cellulose fiber dry material, the particle size, the aggregation state of cellulose molecules, and interparticle interactions are appropriately controlled, making it difficult to form cellulose aggregates that cause defects such as black spots when dispersed in a resin. Therefore, by using the cellulose fiber dry material according to this aspect of the present invention, it is possible to form a resin composite that is highly tough and exhibits a good appearance with few defects such as black spots derived from cellulose.

In one embodiment, the angle of repose of the cellulose fiber dry material is 40° to 60°, preferably 42° or higher, or 44° or higher, or 46° or higher, and preferably 58° or lower, or 56° or lower, or 54° or lower. If the size of the cellulose fiber dry material is too large, dispersion in the resin becomes difficult, but if it is too small, aggregation between particles becomes significant, and the dispersibility in the resin actually worsens. A cellulose fiber dry material with an angle of repose within the above range allows for uniform dispersion of cellulose fibers in the resin due to its appropriate particle size. While the dispersion size in this case is not necessarily extremely fine, the formation of fewer aggregates results in extremely good physical properties (especially toughness) of the resin composite.

The collapse angle of the cellulose fiber dry material is controlled to a range useful for controlling the angle of repose and the difference angle within the scope of this disclosure, and in one embodiment, may be 30° to 50°, or 35° to 48°, or 38° to 46°.

In one embodiment, the difference angle of the cellulose fiber dry (i.e., the difference between the angle of repose and the angle of collapse) is 10° or less, preferably 9° or less, or 8° or less, or 7° or less. Cellulose fiber dry materials with a difference angle within the above range exhibit excellent handling characteristics due to relatively large interparticle interactions (frictional forces, etc.). From the viewpoint of ease of manufacturing the cellulose fiber dry material, the difference angle may be, for example, 1° or more, 2° or more, or 3° or more.

The angle of repose and the angle of collapse are values measured by the methods described in the [Examples] section of this disclosure. The difference angle is calculated as the difference between the angle of repose and the angle of collapse.

In one embodiment, the loosened bulk density of the cellulose fiber dry material is 0.01 g/cm³ or more, preferably 0.05 g/cm³ or more, or 0.08 g/cm³ or more, or 0.1 g/ ^cm³ or more, from the viewpoint of avoiding the inconvenience of particles scattering due to the cellulose fiber dry material being too light, or poor mixing due to the cellulose fiber dry material floating on top of the resin phase when mixed with a fluid resin. Alternatively, the above loosened bulk density is 0.40 g/ ^cm³ or less, preferably 0.38 g/cm³ or ^less , or 0.36 g/ ^cm³ or ^less , or 0.35 g/ ^cm³ or ^less , from the viewpoint of avoiding the inconvenience of particles scattering due to the cellulose fiber dry material being too light, or poor mixing between the cellulose fiber dry material and the resin when ^the cellulose fiber dry material is not too heavy.

The bulk density of the cellulose fiber dry material is controlled to a range useful for controlling the loose bulk and compressibility within the scope of the disclosure, and in one embodiment may be 0.1 g/ ^cm³ to 0.55 g/ ^cm³ , or 0.12 g/ ^cm³ to 0.52 g/ ^cm³ , or 0.13 g/ ^cm³ to 0.2 g/ ^cm³ .

In one embodiment, the compressibility of the cellulose fiber dry material is 20% to 40%. Compressibility represents the degree of volume reduction. To avoid excessive fluidity and suppress natural flow, the compressibility is 20% or higher, preferably 23% or higher, or 25% or higher, or 27% or higher. Alternatively, to ensure good fluidity of the cellulose fiber dry material, the compressibility is 40% or lower, preferably 39% or lower, or 38% or lower, or 37% or lower.

The loose bulk density and the compressed bulk density are values measured by the methods described in the [Examples] section of this disclosure. The compressibility is calculated as follows: Compressibility = (Compressed bulk density - Loose bulk density) / Compressed bulk density.

The content of particles with a particle size of 710 μm or less in the cellulose fiber dry body is 50 to 90% by mass in one embodiment, preferably 55 to 85% by mass, or 60 to 80% by mass, or 63 to 77% by mass. The content of particles with a particle size greater than 710 μm and less than or equal to 1000 μm is preferably 10 to 30% by mass, or 12 to 25% by mass. The content of particles with a particle size greater than 1000 μm is preferably 1 to 22% by mass, or 5 to 10% by mass. In the cellulose fiber dry body, having small particles with a particle size of 710 μm or less as the main component facilitates the dispersion of the cellulose fiber dry body in the resin, improving toughness while suppressing screen mesh clogging. Furthermore, by including an appropriate amount of particles with a particle size greater than 710 μm, rigidity can be achieved, thus obtaining a resin composite with an excellent balance of physical properties. The particle size distribution of the cellulose fiber dry body is the value measured by the method described in the [Examples] section of this disclosure.

In one embodiment, the average particle size of the dried cellulose fiber is preferably 50 μm or more, or 100 μm or more, or 200 μm or more, and preferably 5000 μm or less, or 4000 μm or less, or 3000 μm or less, or 2000 μm or less. The above average particle size is a value measured by laser diffraction/scattering.

In one embodiment, the moisture content of the cellulose fiber dry product may be 30% by mass or less, 20% by mass or less, or 10% by mass or less. The moisture content may be 0% by mass, but from the viewpoint of ease of manufacturing the cellulose fiber dry product, it may be, for example, 0.1% by mass or more, 1% by mass or more, or 1.5% by mass or more. The moisture content is a value measured using an infrared heating type moisture meter.

Natural cellulose and regenerated cellulose can be used as raw materials for dried cellulose fibers. Natural cellulose can include wood pulp obtained from wood species (hardwood or softwood), non-wood pulp obtained from non-wood species (cotton, bamboo, hemp, bagasse, kenaf, cotton linters, sisal, straw, etc.), and cellulose fiber aggregates produced by animals (e.g., sea squirts), algae, and microorganisms (e.g., acetic acid bacteria). Regenerated cellulose can include regenerated cellulose fibers (viscose, cupro, Tencel, etc.), cellulose derivative fibers, and ultrafine threads of regenerated cellulose or cellulose derivatives obtained by electrospinning.

In one embodiment, the cellulose fiber is a cellulose nanofiber. Cellulose nanofiber refers to fine cellulose fibers obtained by treating pulp, etc., with hot water at 100°C or higher to hydrolyze and weaken the hemicellulose, and then defibrating it using a grinding method such as a high-pressure homogenizer, microfluidizer, ball mill, disc mill, or mixer (e.g., homomixer). In one embodiment, the cellulose nanofiber has a number-average fiber diameter of 1 nm to 1000 nm. The cellulose fiber may also be chemically modified as described later.

The slurry can be prepared by dispersing cellulose fibers (e.g., cellulose nanofibers obtained through the above defibration process) in a liquid medium. Dispersion may be performed using a high-pressure homogenizer, microfluidizer, ball mill, disc mill, mixer (e.g., homomixer), etc. For example, the product of the above defibration process may be obtained as the product of the slurry preparation step of this disclosure. In addition to water, the liquid medium in the slurry may further contain other liquid media (e.g., organic solvents) either alone or in combination of two or more. As organic solvents, commonly used water-miscible organic solvents can be used, such as: alcohols with boiling points of 50°C to 170°C (e.g., methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, t-butanol, etc.); ethers (e.g., propylene glycol monomethyl ether, 1,2-dimethoxyethane, diisopropyl ether, tetrahydrofuran, 1,4-dioxane, etc.); carboxylic acids (e.g., formic acid, acetic acid, lactic acid, etc.); esters (e.g., ethyl acetate, vinyl acetate, etc.); ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, etc.); nitrogen-containing solvents (dimethylformamide, dimethylacetamide, acetonitrile, etc.). In a typical embodiment, the liquid medium in the slurry is substantially water only. In addition to cellulose fibers and the liquid medium, the slurry may also contain additional components described later (dispersants, binders, antioxidants, preservatives, thickeners, etc.).

Cellulose fiber raw materials contain alkali-soluble components and sulfuric acid-insoluble components (such as lignin). Therefore, purification processes such as deligninization by pulping and bleaching may be used to reduce these components. On the other hand, purification processes such as deligninization by pulping and bleaching cleave the molecular chains of cellulose, changing the weight-average molecular weight and number-average molecular weight. Therefore, it is desirable that the purification and bleaching processes of cellulose fiber raw materials control the weight-average molecular weight and the ratio of weight-average molecular weight to number-average molecular weight of cellulose to such an extent that they do not deviate from an appropriate range.

Furthermore, purification processes such as lignin removal through pulping and bleaching reduce the molecular weight of cellulose molecules. Therefore, there are concerns that these processes may lead to a decrease in the molecular weight of cellulose and an increase in the proportion of alkali-soluble components due to the alteration of the cellulose fiber raw material. Since alkali-soluble components have poor heat resistance, it is desirable that the purification and bleaching processes of the cellulose fiber raw material be controlled so that the amount of alkali-soluble components contained in the cellulose fiber raw material remains below a certain value.

In one embodiment, the number-average fiber diameter of the cellulose fibers is preferably 2 to 1000 nm, from the viewpoint of obtaining a good effect of improving physical properties by the cellulose fibers. More preferably, the number-average fiber diameter of the cellulose fibers is 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 500 nm or less, or 450 nm or less, or 400 nm or less, or 350 nm or less, or 300 nm or less, or 250 nm or less.

The average L/D ratio of cellulose fibers is preferably 50 or higher, or 80 or higher, or 100 or higher, or 120 or higher, or 150 or higher, from the viewpoint of effectively improving the mechanical properties of the resin composite containing cellulose fibers with a small amount of cellulose fibers. While there is no particular upper limit, it is preferably 5000 or lower from the viewpoint of ease of handling.

In this disclosure, the length, diameter, and L/D ratio of each cellulose fiber are determined by dispersing an aqueous dispersion of cellulose fibers using a high-shear homogenizer (e.g., Nippon Seiki Co., Ltd., product name "Excel Auto Homogenizer ED-7") under the following conditions: rotation speed 15,000 rpm × 5 minutes. The aqueous dispersion is then diluted with pure water to 0.1–0.5% by mass, cast onto mica, air-dried, and used as a measurement sample. The sample is then measured using a high-resolution scanning microscope (SEM) or atomic force microscope (AFM). Specifically, the length (L) and diameter (D) of 100 randomly selected cellulose fibers are measured in an observation field adjusted to the magnification so that at least 100 cellulose fibers are visible, and the ratio (L/D) is calculated. For each cellulose fiber, the numerical average values of length (L), diameter (D), and ratio (L/D) are calculated.

Alternatively, the length, diameter, and L/D ratio of cellulose fibers in the resin composite can be confirmed by measuring the solid resin composite as a sample using the measurement method described above.

Alternatively, the length, diameter, and L/D ratio of cellulose fibers in the resin composite can be determined by dissolving the resin components in the resin composite in an organic or inorganic solvent capable of dissolving the resin components, separating the cellulose fibers, thoroughly washing them with the solvent, preparing an aqueous dispersion by replacing the solvent with pure water, diluting the cellulose fiber concentration with pure water to 0.1-0.5% by mass, casting it onto mica, air-drying it, and measuring it using the measurement method described above. In this case, at least 100 randomly selected cellulose fibers should be measured.

The crystallinity of the cellulose fibers is preferably 55% or higher. When the crystallinity is within this range, the mechanical properties (strength, dimensional stability) of the cellulose fibers themselves are high, and therefore, when the cellulose fibers are dispersed in the resin, the strength and dimensional stability of the resin composite tend to be high. A more preferable lower limit for the crystallinity is 60%, even more preferably 70%, and most preferably 80%. There is no particular upper limit for the crystallinity of the cellulose fibers; higher is preferable, but from a production standpoint, a preferable upper limit is 99%.

Between the microfibrils and between the microfibril bundles of plant-derived cellulose, alkali-soluble polysaccharides such as hemicellulose and acid-insoluble components such as lignin are present. Hemicellulose is a polysaccharide composed of sugars such as mannan and xylan, and it plays a role in linking microfibrils by hydrogen bonding with cellulose. Lignin is a compound with an aromatic ring, and it is known to be covalently bonded to hemicellulose in the cell walls of plants. If the residual amount of impurities such as lignin in the cellulose fibers is high, discoloration may occur due to the heat during processing. Therefore, from the viewpoint of suppressing discoloration of the resin composite during extrusion and molding, it is desirable to keep the crystallinity of the cellulose fibers within the above-mentioned range.

The degree of crystallinity referred to here, when the cellulose is type I cellulose crystal (derived from natural cellulose), can be determined by the Segal method using the following formula from the diffraction pattern (2θ/deg. is 10 to 30) obtained by measuring the sample by wide-angle X-ray diffraction.
Crystallinity (%) = ([Diffraction intensity due to the (200) plane at 2θ/deg. = 22.5] - [Diffraction intensity due to amorphous material at 2θ/deg. = 18]) / [Diffraction intensity due to the (200) plane at 2θ/deg. = 22.5] × 100

Furthermore, if the cellulose is a type II cellulose crystal (derived from regenerated cellulose), the degree of crystallinity can be determined by the following formula using wide-angle X-ray diffraction, from the absolute peak intensity h0 at 2θ = 12.6°, which is attributed to the (110) plane peak of the type II cellulose crystal, and the peak intensity h1 from the baseline at this interplanar spacing.
Crystallinity (%) = h1 /h0 ×100

Known crystalline forms of cellulose include Type I, Type II, Type III, and Type IV. Among these, Type I and Type II are particularly widely used, while Type III and Type IV, although obtained on a laboratory scale, are not commonly used on an industrial scale. The cellulose fibers of this disclosure exhibit relatively high structural mobility, and by dispersing these cellulose fibers in a resin, a resin composite with a lower coefficient of thermal expansion and superior strength and elongation during tensile and bending deformation can be obtained. Therefore, cellulose fibers containing Type I or Type II cellulose crystals are preferred, and cellulose fibers containing Type I cellulose crystals and having a crystallinity of 55% or higher are more preferred.

Furthermore, the degree of polymerization of the cellulose fibers is preferably 100 or higher, more preferably 150 or higher, more preferably 200 or higher, more preferably 300 or higher, more preferably 400 or higher, more preferably 450 or higher, preferably 3500 or lower, more preferably 3300 or lower, more preferably 3200 or lower, more preferably 3100 or lower, and more preferably 3000 or lower.

From the viewpoint of processability and mechanical property development, it is desirable to keep the degree of polymerization of the cellulose fibers 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 development, it is desirable that it is not too low.

The degree of polymerization of cellulose fibers refers to the average degree of polymerization measured according to the reduction ratio viscosity method using copper ethylenediamine solution, as described in the confirmation test (3) of the "Fifteenth Revised Japanese Pharmacopoeia Commentary (published by Hirokawa Shoten)".

In one embodiment, the weight-average molecular weight (Mw) of the cellulose fiber is 100,000 or more, more preferably 200,000 or more. The ratio of weight-average molecular weight to number-average molecular weight (Mn) (Mw/Mn) is 6 or less, preferably 5.4 or less. A larger weight-average molecular weight means fewer end groups in the cellulose molecule. Also, since the ratio of weight-average molecular weight to number-average molecular weight (Mw/Mn) represents the width of the molecular weight distribution, a smaller Mw/Mn means fewer end groups in the cellulose molecule. Since the end groups of cellulose molecules are the starting points for thermal decomposition, when the weight-average molecular weight of the cellulose fiber is large, and at the same time the width of the molecular weight distribution is narrow, a particularly heat-resistant cellulose fiber and a resin composite containing cellulose fiber and resin can be obtained. From the viewpoint of the availability of cellulose fiber raw materials, the weight-average molecular weight (Mw) of the cellulose fiber may be, for example, 600,000 or less, or 500,000 or less. The ratio of weight-average molecular weight to number-average molecular weight (Mn) (Mw/Mn) may be, for example, 1.5 or higher, or 2 or higher, from the viewpoint of ease of cellulose fiber production. Mw can be controlled within the above range by selecting a cellulose fiber raw material having an Mw appropriate to the purpose, and by appropriately performing physical and/or chemical treatments on the cellulose fiber raw material within an appropriate range. Mw/Mn can also be controlled within the above range by selecting a cellulose fiber raw material having an Mw/Mn appropriate to the purpose, and by appropriately performing physical and/or chemical treatments on the cellulose fiber raw material within an appropriate range. Examples of physical treatments for both Mw and Mw/Mn control include dry or wet grinding using microfrudizers, ball mills, disc mills, etc., and applying mechanical forces such as impact, shear, shear, and friction using grinders, homomixers, high-pressure homogenizers, ultrasonic devices, etc. Examples of chemical treatments include pulverization, bleaching, acid treatment, and regenerative celluloseization.

The weight-average molecular weight and number-average molecular weight of cellulose fibers referred to here are values obtained by dissolving the cellulose fibers in N,N-dimethylacetamide to which lithium chloride has been added, and then determining them by gel permeation chromatography using N,N-dimethylacetamide as the solvent.

Methods for controlling the degree of polymerization (i.e., average degree of polymerization) or molecular weight of cellulose fibers include hydrolysis. Hydrolysis promotes the depolymerization of amorphous cellulose within the cellulose fibers, reducing the average degree of polymerization. Simultaneously, hydrolysis removes impurities such as hemicellulose and lignin in addition to the amorphous cellulose, resulting in a porous structure within the fibers.

The hydrolysis method is not particularly limited, but examples include acid hydrolysis, alkaline hydrolysis, hydrothermal decomposition, steam explosion, and microwave decomposition. These methods may be used individually or in combination of two or more. In the acid hydrolysis method, for example, α-cellulose obtained as pulp from fibrous plants is used as the cellulose fiber raw material, and while dispersed in an aqueous medium, an appropriate amount of protic acid, carboxylic acid, Lewis acid, heteropoly acid, etc. is added, and the average degree of polymerization can be easily controlled by heating while stirring. The reaction conditions such as temperature, pressure, and time vary depending on the cellulose species, cellulose concentration, acid species, acid concentration, etc., but are adjusted appropriately to achieve the desired average degree of polymerization. For example, one condition is to use an aqueous solution of mineral acid at 2% by mass or less and treat the cellulose fibers at 100°C or higher under pressure for 10 minutes or more. Under these conditions, the catalytic component such as acid penetrates into the cellulose fiber, promoting hydrolysis, reducing the amount of catalytic component used, and making subsequent purification easier. Furthermore, the dispersion of cellulose fiber raw materials during hydrolysis may contain a small amount of organic solvent in addition to water, as long as it does not impair the effects of the present invention.

The alkali-soluble polysaccharides that cellulose fibers may contain include not only hemicellulose but also β-cellulose and γ-cellulose. Alkali-soluble polysaccharides are understood by those skilled in the art 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). Since alkali-soluble polysaccharides are polysaccharides containing hydroxyl groups and have poor heat resistance, they can decompose when heated, cause yellowing during thermal aging, and reduce the strength of cellulose fibers. Therefore, it is preferable to have a low alkali-soluble polysaccharide content in cellulose fibers.

In one embodiment, the average content of alkali-soluble polysaccharides in the cellulose fibers 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 cellulose fibers, from the viewpoint of obtaining good dispersibility of the cellulose fibers. The above content may be 1% by mass or more, 2% by mass or more, or 3% by mass or more, from the viewpoint of ease of manufacturing the cellulose fibers.

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

In one embodiment, the average content of acid-insoluble components in the cellulose fibers 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 cellulose fibers, from the viewpoint of avoiding a decrease in the heat resistance of the cellulose fibers and the resulting discoloration. The above content may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more, from the viewpoint of ease of manufacturing the cellulose fibers.

The average acid-insoluble component content is determined using the Claesson 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 this industry as a method for measuring lignin content. The sample is stirred in sulfuric acid solution to dissolve cellulose and hemicellulose, etc., and then filtered through glass fiber filter paper. The resulting residue contains the acid-insoluble components. The acid-insoluble component content is calculated from the weight of these components, and the average of the number of acid-insoluble component content values calculated for three samples is taken as the average acid-insoluble component content.

The thermal decomposition onset temperature ( _TD ) of cellulose fibers is, in one embodiment, 270°C or higher, preferably 275°C or higher, more preferably 280°C or higher, and even more preferably 285°C or higher, from the viewpoint of exhibiting the heat resistance and mechanical strength desired for automotive applications and the like. A higher thermal decomposition onset temperature is preferable, but from the viewpoint of ease of manufacturing cellulose fibers, it may be, for example, 320°C or lower, or 300°C or lower.

In this disclosure, _TD is a value obtained from a graph in thermogravimetric (TG) analysis, where the horizontal axis is temperature and the vertical axis is weight retention percentage, as shown in the explanatory diagram in Figure 2 (Figure 2(B) is an enlarged view of Figure 2(A)). Starting from the weight of cellulose fiber at 150°C (a state in which almost all moisture has been removed) (weight loss of 0 wt%), the temperature is further increased to obtain a straight line passing through the temperature at a 1 wt% weight loss (T _1% ) and the temperature at a 2 wt% weight loss (T _2% ). _TD is defined as the temperature at the point where this straight line intersects with a horizontal line (baseline) passing through the starting point of 0 wt% weight loss.

The 1% weight loss temperature (T _1% ) is the temperature at which the weight decreases by 1% by weight, starting from the weight at 150°C, when the heating method _TD described above is continued.

The weight loss rate of cellulose fibers at 250°C (T _250°C ) is the weight loss rate when cellulose fibers are held at 250°C under a nitrogen flow for 2 hours, as determined by TG analysis.

(chemical modification)
The cellulose fibers may be chemically modified. For example, the cellulose fibers may be chemically modified beforehand at the raw pulp or linter stage, during or after the defibration process, or they may be chemically modified during or after the slurry preparation process, or during or after the drying (granulation) process.

As modifying agents for cellulose fibers, compounds that react with the hydroxyl groups of cellulose can be used, including esterifying agents, etherifying agents, and silylating agents. In a preferred embodiment, chemical modification is acylation using an esterifying agent. Preferred esterifying agents include acid halides, acid anhydrides, vinyl carboxylates, and carboxylic acids.

The acid halide may be at least one selected from the group consisting of compounds represented by the following formula (1).
R ¹ -C(=O)-X (1)
(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 is 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 these, acid chlorides are particularly suitable due to their reactivity and ease of handling. In the reaction of acid halides, one or more alkaline compounds may be added to act as a catalyst and to neutralize the acidic by-products. 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.

Any suitable acid anhydride can be used as the acid anhydride. 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;
Alicyclic monocarboxylic acid anhydrides such as cyclohexanecarboxylic acid and tetrahydrobenzoic acid;
Aromatic monocarboxylic anhydrides such as benzoic acid and 4-methylbenzoic acid;
Examples of dibasic carboxylic acid anhydrides include saturated aliphatic dicarboxylic anhydrides such as succinic anhydride and adipic acid, unsaturated aliphatic dicarboxylic anhydrides such as maleic anhydride and itaconic anhydride, alicyclic dicarboxylic anhydrides such as 1-cyclohexene-1,2-dicarboxylic anhydride, hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride, and aromatic dicarboxylic anhydrides such as phthalic anhydride and naphthalic anhydride;
Examples of polybasic carboxylic acid anhydrides with three or more bases include (anhydride) polycarboxylic acids such as trimellitic anhydride and pyromellitic anhydride.
Furthermore, in the reaction of acid anhydrides, one or more acidic compounds such as sulfuric acid, hydrochloric acid, or phosphoric acid, or Lewis acids (for example, Lewis acid compounds represented as MYn, where M represents a metalloid element such as B, As, or Ge, or a base metal element such as Al, Bi, or In, or a transition metal element such as Ti, Zn, or Cu, or a lanthanide element; n is an integer corresponding to the valence of M, representing 2 or 3; and Y represents a halogen atom, OAc, _OCOCF3 , _ClO4 , _SbF6 , _PF6 , or _OSO2CF3 ( _OTf )), or alkaline compounds such as triethylamine or pyridine may be added as catalysts.

As for vinyl carboxylates, see formula (1):
R-COO-CH=CH ₂ ...Formula (1)
A vinyl carboxylate ester represented by the formula {wherein R is any 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, or an aryl group having 6 to 24 carbon atoms} is preferred. The vinyl carboxylate ester 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 octoate, vinyl adipate, vinyl methacrylate, vinyl crotate, vinyl pivalate, vinyl octoate, vinyl benzoate, and vinyl cinnamate. In esterification reactions with vinyl carboxylates, 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 bicarbonates, primary to tertiary amines, quaternary ammonium salts, imidazoles and their derivatives, pyridines and their derivatives, and alkoxides may be added.

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

Primary, secondary, and tertiary amines refer to primary, secondary, and tertiary amines. 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.

Examples of imidazoles and their derivatives include 1-methylimidazole, 3-aminopropylimidazole, and carbonyldiimidazole.

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.

Examples of carboxylic acids include at least one selected from the group consisting of compounds represented by the following formula (1).
R-COOH…(1)
(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, cyclohexanecarboxylic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, pivalic acid, methacrylic acid, crotonic acid, pivalic acid, octic 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, particularly acetic acid, is preferred from the viewpoint of reaction efficiency.
Furthermore, in the reaction of carboxylic acids, one or more acidic compounds such as sulfuric acid, hydrochloric acid, or phosphoric acid, or Lewis acids (for example, Lewis acid compounds represented as MYn, where M represents a metalloid element such as B, As, or Ge, or a base metal element such as Al, Bi, or In, or a transition metal element such as Ti, Zn, or Cu, or a lanthanide element; n is an integer corresponding to the valence of M, representing 2 or 3; and Y represents a halogen atom, _OAc , _OCOCF3 , _ClO4 , _SbF6 , _PF6 , or _OSO2CF3 (OTf)), or alkaline compounds such as triethylamine or pyridine may be added as catalysts.

Among these esterification reagents, at least one selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, vinyl acetate, vinyl propionate, vinyl butyrate, and acetic acid, with acetic anhydride and vinyl acetate being particularly preferred from the viewpoint of reaction efficiency, is preferred.

When cellulose fibers in a cellulose fiber dry are chemically modified (e.g., by hydrophobication such as acylation), the dispersibility of the dry in the resin tends to be good. However, the cellulose fiber dry of this disclosure can exhibit good dispersibility in the resin even when unsubstituted or with a low degree of substitution. When the cellulose fibers in the cellulose fiber dry are esterified cellulose fibers, the degree of acyl substitution (DS) is preferably 0.1 or higher, or 0.2 or higher, or 0.25 or higher, or 0.3 or higher, or 0.5 or higher, in order to obtain esterified cellulose fibers and resin composites containing them with a high thermal decomposition initiation temperature. Furthermore, since unmodified cellulose skeletons remain in the esterified cellulose fibers, the degree of acyl substitution (DS) is preferably 1.2 or lower, or 1.0 or lower, or 0.8 or lower, or 0.7 or lower, or 0.6 or lower, or 0.5 or lower, in order to obtain esterified cellulose fibers and resin composites containing them that combine high tensile strength and dimensional stability derived from cellulose with a high thermal decomposition initiation temperature derived from chemical modification.

When the modifying group of chemically modified cellulose fibers is an acyl group, the degree of acyl substitution (DS) can be calculated from the reflectivity infrared absorption spectrum of the esterified cellulose fiber based on the peak intensity ratio of the peak derived from the acyl group to the peak derived from the cellulose skeleton. The peak of the C=O absorption band based on the acyl group appears at 1730 ^cm⁻¹ , and the peak of the C-O absorption band based on the cellulose skeleton appears at 1030 ^cm⁻¹ (see Figure 1). The DS of esterified cellulose fibers is calculated by creating a correlation graph between the DS obtained from solid-state NMR measurements of esterified cellulose fibers (described later) and the modification rate (IR index 1030), which is defined as the ratio of the peak intensity of the C=O absorption band based on the acyl group to the peak intensity of the C-O absorption band of the cellulose skeleton. The calibration curve of substitution DS calculated from the correlation graph is: DS = 4.13 × IR index (1030).
This can be obtained by using [this method].

The method for calculating the DS of esterified cellulose fibers by solid NMR involves performing ^13C solid NMR measurements on freeze-ground esterified cellulose fibers. The DS can be calculated using the following formula, which compares the area intensity (Inf) of the signal attributed to a single carbon atom derived from the modifying group with the total area intensity (Inp) of the signals attributed to carbon atoms C1-C6 derived from the pyranose ring of cellulose that appear in the range of 50 ppm to 110 ppm.
DS=(Inf)×6/(Inp)
For example, if the modifying group is an acetyl group, you can use the 23 ppm signal assigned to _-CH3 .
The conditions used for ^13C solid-state NMR measurement are, for example, as follows:
Equipment: Bruker Biospin Avance500WB
Frequency: 125.77 MHz
Measurement method: DD/MAS method Waiting time: 75 seconds
NMR sample tube: 4 mm diameter
Total number of times: 640 (approximately 14 hours)
MAS: 14,500Hz
Chemical shift standard: Glycine (External standard: 176.03 ppm)

The DS non-uniformity ratio (DSs/DSt), defined as the ratio of the degree of modification of the fiber surface (DSs) to the degree of modification of the entire fiber (DSt) (which is synonymous with the degree of acyl substitution (DS) above) of chemically modified cellulose fibers, is preferably 1.05 or higher. The larger the value of the DS non-uniformity ratio, the more pronounced the sheath-core-like non-uniform structure (i.e., a structure in which the fiber surface is highly chemically modified while the fiber center retains a structure close to the original unmodified cellulose), and while possessing high tensile strength and dimensional stability derived from cellulose, it is possible to improve the affinity with the resin when compounded with the resin, and improve the dimensional stability of the resin composite. The DS non-uniformity ratio is more preferably 1.1 or higher, or 1.2 or higher, or 1.3 or higher, or 1.5 or higher, or 2.0, and from the viewpoint of ease of manufacturing chemically modified cellulose fibers, it is preferably 30 or lower, or 20 or lower, or 10 or lower, or 6 or lower, or 4 or lower, or 3 or lower.
The value of DSs varies depending on the degree of modification of the esterified cellulose fiber, but as an example, it is preferably 0.1 or higher, more preferably 0.2 or higher, even more preferably 0.3 or higher, even more preferably 0.5 or higher, preferably 3.0 or lower, more preferably 2.5 or lower, particularly preferably 2.0 or lower, even more preferably 1.5 or lower, particularly preferably 1.2 or lower, and most preferably 1.0 or lower. The preferred range for DSt is as described above for acyl substituents (DS).

A smaller coefficient of variation (CV) of the DS heterogeneity ratio of chemically modified cellulose fibers is preferable because it reduces the variability in various physical properties of the resin composite. Preferably, the coefficient of variation is 50% or less, or 40% or less, or 30% or less, or 20% or less. The coefficient of variation can be further reduced in a method where chemical modification is performed after defibrillation of the cellulose fiber raw material (i.e., a sequential method), while it can be increased in a method where defibrillation and chemical modification of the cellulose fiber raw material are performed simultaneously (i.e., a simultaneous method). Although the mechanism of action is not clear, it is thought that in the simultaneous method, chemical modification proceeds more easily in the fine fibers generated in the initial stages of defibrillation, and as the hydrogen bonds between cellulose microfibrils decrease due to chemical modification, defibrillation progresses further, resulting in an increase in the coefficient of variation of the DS heterogeneity ratio.

The coefficient of variation (CV) of the DS heterogeneity ratio can be calculated using the following formula: 100 g of an aqueous dispersion of chemically modified cellulose fibers (solid content of 10% by mass or more) is taken, and 10 g portions are freeze-dried and ground to obtain the measurement samples. After calculating the DS heterogeneity ratio from the DSst and DSs of the 10 samples, the coefficient of variation (CV) can be calculated from the standard deviation (σ) and arithmetic mean (μ) of the DS heterogeneity ratios among the 10 obtained samples.
DS heterogeneity ratio = DSs/DSt
Coefficient of variation (%) = Standard deviation σ / Arithmetic mean μ × 100

The method for calculating DSs is as follows: Esterified cellulose fibers, powdered by freeze-grinding, are placed on a 2.5 mm diameter dish-shaped sample stage, the surface is pressed down to flatten it, and measurement is performed by X-ray photoelectron spectroscopy (XPS). The XPS spectrum reflects the constituent elements and chemical bonding state of only the surface layer of the sample (typically a few nm). Peak separation is performed on the obtained C1s spectrum, and the area intensity (Ixp) of the peak attributed to a single carbon atom derived from the modifying group relative to the area intensity (Ixf) of the peak attributed to a single carbon atom derived from the pyranose ring of cellulose (289 eV, C-C bond) can be calculated using the following formula.
DSs=(Ixf)×5/(Ixp)
For example, if the modifying group is an acetyl group, after separating the C1s spectrum at 285 eV, 286 eV, 288 eV, and 289 eV, the 289 eV peak can be used for Ixp and the peak derived from the O-C=O bond of the acetyl group (286 eV) can be used for Ixf.
The conditions used for XPS measurement are as follows, for example:
Equipment used: ULVAC-FI VersaProbe II
Excitation source: mono. AlKα 15kV × 3.33mA
Analysis size: Approximately 200 μmφ
Photoelectron extraction angle: 45°
Capture area Narrow scan: C 1s, O 1s
Pass Energy: 23.5eV

[Additional ingredients]
The dried cellulose fiber may further contain additional components such as dispersants, binders, antioxidants, preservatives, and thickeners, in addition to the cellulose fiber.

(Dispersant)
The dispersant contributes to improving the dispersibility of cellulose fibers in the resin. The dispersant may be a single substance or a mixture of two or more substances. In the latter case, the characteristic values of this disclosure (e.g., melting point, molecular weight, HLB value, SP value) refer to the values of the mixture.

The melting point of the dispersant may be 80°C or lower, or 70°C or lower, and may be -100°C or higher, or -50°C or higher, in order to allow the dispersant to more uniformly coat the cellulose fibers and to disperse the cellulose fibers more uniformly in the resin. The number-average molecular weight of the dispersant may be 1000 or higher, or 2000 or higher, and may be 50000 or lower, or 20000 or lower, in order to allow the dispersant to more uniformly coat the cellulose fibers and to disperse the cellulose fibers more uniformly in the resin. The number-average molecular weight of the dispersant is determined using gel permeation chromatography and converted to standard polystyrene equivalent.

The dispersant is preferably a water-soluble polymer from the viewpoint of suppressing the aggregation of cellulose fibers. In this disclosure, "water-soluble" means dissolving 0.1 g or more in 100 g of water at 23°C. Furthermore, it is even more preferable for the dispersant to have both a hydrophilic segment and a hydrophobic segment (i.e., an amphiphilic molecule) from the viewpoint of more uniformly dispersing cellulose fibers in the resin. Examples of amphiphilic molecules include those with a carbon atom as the basic skeleton and functional groups composed of elements selected from carbon, hydrogen, oxygen, nitrogen, chlorine, sulfur, and phosphorus. It is also preferable that the molecule has the above structure, and that an inorganic compound is chemically bonded to the above functional group. The hydrophilic segment has good affinity with the surface of the cellulose fibers, and the hydrophobic segment suppresses the aggregation of cellulose fibers through the hydrophilic segment and is also easily compatible with the resin. Therefore, it is preferable that the hydrophilic segment and the hydrophobic segment exist within the same molecule in the dispersant.

The HLB value of the dispersant is preferably 0.1 or more and less than 8.0. The HLB value is a value that indicates the balance between hydrophobicity and hydrophilicity of a surfactant, and takes a value from 1 to 20, with a smaller number indicating stronger hydrophobicity and a larger number indicating stronger hydrophilicity. In this disclosure, the HLB value is a value obtained by the following Griffin method formula. In the formula below, "sum of formula weights of hydrophilic groups / molecular weight" is the mass % of the hydrophilic groups.
Formula 1) Griffin method: HLB value = 20 × (sum of formula weights of hydrophilic groups / molecular weight)

The lower limit of the HLB value of the dispersant is preferably 0.1, more preferably 0.2, and most preferably 1, from the viewpoint of easy solubility in water. Furthermore, the upper limit of the HLB value is preferably less than 8, more preferably 7.5, and most preferably 7, from the viewpoint of uniform dispersion of cellulose fibers in the resin.

In a typical embodiment, the hydrophilic segment is a portion that exhibits good affinity to cellulose fibers by containing a hydrophilic structure (e.g., one or more hydrophilic groups selected from hydroxyl groups, carboxyl groups, carbonyl groups, amino groups, ammonium groups, amide groups, sulfo groups, etc.). Examples of hydrophilic segments include polyethylene glycol segments (i.e., segments of multiple oxyethylene units) (PEG blocks), segments containing repeating units including quaternary ammonium salt structures, polyvinyl alcohol segments, polyvinylpyrrolidone segments, polyacrylic acid segments, carboxyvinyl polymer segments, cationized guar gum segments, hydroxyethylcellulose segments, methylcellulose segments, carboxymethylcellulose segments, polyurethane soft segments (specifically diol segments), and the like. In a preferred embodiment, the hydrophilic segment contains oxyethylene units.

Examples of hydrophobic segments include segments having alkylene oxide units with 3 or more carbon atoms (e.g., PPG blocks), and segments containing the following polymer structures:
Acrylic polymers, styrene resins, vinyl chloride resins, vinylidene chloride resins, polyolefin resins, polyhexamethylene adipamide (6,6 nylon), polyhexamethylene azeramide (6,9 nylon), polyhexamethylene sevacamide (6,10 nylon), polyhexamethylene dodecanoamide (6,12 nylon), polybis(4-aminocyclohexyl)methanedodecane, etc., polycondensates of C4-C12 organic dicarboxylic acids and C2-C13 organic diamines, polycondensates of ω-amino acids (e.g., ω-aminoundecanoic acid) (e.g., polyundecanoamide (1) Amino acid lactams containing ring-opened polymers of lactams, such as nylon 1, polycapramid (nylon 6), which is a ring-opened polymer of ε-aminocaprolactam, and polylauric lactam (nylon 12), which is a ring-opened polymer of ε-aminolaurolactam; polymers composed of diamines and dicarboxylic acids; polyacetal resins; polycarbonate resins; polyester resins; polyphenylene sulfide resins; polysulfone resins; polyetherketone resins; polyimide resins; fluorine resins; hydrophobic silicone resins; melamine resins; epoxy resins; and phenolic resins.

In a preferred embodiment, the dispersant has a PEG block as a hydrophilic group and a PPG block as a hydrophobic group within its molecule.

The dispersant may have a graft copolymer structure and/or a block copolymer structure. These structures may be single or in combination of two or more. In the case of two or more structures, a polymer alloy may be used. Furthermore, partially modified or terminally modified (acid-modified) copolymers of these copolymers may also be used.

The structure of the dispersant is not particularly limited, but when the hydrophilic segment is A and the hydrophobic segment is B, examples include AB-type block copolymers, ABA-type block copolymers, BAB-type block copolymers, ABAB-type block copolymers, ABABA-type block copolymers, BABAB-type copolymers, tribranched copolymers containing A and B, tetrabranched copolymers containing A and B, star-shaped copolymers containing A and B, monocyclic copolymers containing A and B, polycyclic copolymers containing A and B, and cage-shaped copolymers containing A and B.

The structure of the dispersant is preferably an AB-type block copolymer, an ABA-type triblock copolymer, a tribranched copolymer containing A and B, or a tetrabranched copolymer containing A and B, and more preferably an ABA-type triblock copolymer, a tribranched structure (i.e., a tribranched copolymer containing A and B), or a tetrabranched structure (i.e., a tetrabranched copolymer containing A and B). To ensure good affinity with cellulose fibers, the structure of the dispersant is desirable to be as described above.

Suitable examples of dispersants include copolymers obtained by using one or more compounds that provide a hydrophilic segment (e.g., polyethylene glycol) and one or more compounds that provide a hydrophobic segment (e.g., polypropylene glycol, poly(tetramethylene ether) glycol (PTMEG), polybutadienediol, etc.) (e.g., block copolymers of propylene oxide and ethylene oxide, block copolymers of tetrahydrofuran and ethylene oxide). The dispersant may be used alone or in combination of two or more. When two or more are used in combination, they may be used as a polymer alloy. Furthermore, modified copolymers (e.g., those modified with at least one compound selected from unsaturated carboxylic acids, their acid anhydrides, or their derivatives) can also be used.

Among these, copolymers of polyethylene glycol and polypropylene glycol, copolymers of polyethylene glycol and poly(tetramethylene ether) glycol (PTMEG), and mixtures thereof are preferred from the viewpoint of heat resistance (odor resistance) and mechanical properties. Copolymers of polyethylene glycol and polypropylene glycol are more preferred from the viewpoint of handling ease and cost.

In a typical embodiment, dispersants have a cloud point. When the temperature of an aqueous solution of a nonionic surfactant with polyether chains, such as polyoxyethylene chains, as its hydrophilic portion is increased, the previously transparent or translucent solution becomes cloudy at a certain temperature (this temperature is called the cloud point). That is, when an aqueous solution that is transparent or translucent at low temperatures is heated, the solubility of the nonionic surfactant decreases sharply beyond a certain temperature, causing the previously dissolved surfactants to aggregate, become cloudy, and separate from the water. This is thought to be because at high temperatures, the nonionic surfactant loses its hydration ability (the hydrogen bonds between the polyether chains and water break, causing a sharp decrease in solubility in water). The cloud point tends to be lower the longer the polyether chain. Since dispersants dissolve in water in any proportion below the cloud point, the cloud point serves as a measure of hydrophilicity in dispersants.

The cloud point of a dispersant can be measured using the following method: Using a tuning fork vibrating viscometer (e.g., SV-10A, manufactured by A&D Company, Limited), aqueous solutions of the dispersant are adjusted to 0.5% by mass, 1.0% by mass, and 5% by mass, and measurements are taken at temperatures ranging from 0 to 100°C. At this time, the point where an inflection point (a change in viscosity or the point at which the aqueous solution becomes cloudy) is observed at each concentration is defined as the cloud point.

The lower limit of the cloud point of the dispersant is preferably 10°C, more preferably 20°C, and most preferably 30°C, from the viewpoint of handling ease. The upper limit of the cloud point is not particularly limited, but is preferably 120°C, more preferably 110°C, even more preferably 100°C, and most preferably 60°C. It is desirable that the cloud point of the dispersant be within the above range to ensure good affinity with cellulose fibers.

As a dispersant, one with a solubility parameter (SP value) of 7.25 or higher is more preferable. Having an SP value within this range improves the dispersibility of cellulose fibers in the resin.

According to Foders' literature (R.F. Foders: Polymer Engineering & SCienCe, vol. 12(10), pp. 2359-2370 (1974)), the SP value depends on both the cohesive energy density and molar molecular weight of the substance, and these are thought to depend on the type and number of substituents in the substance. According to Ueda et al.'s literature (Paint Research, No. 152, OCt. 2010), the SP values (Cal/ ^Cm³ ) ^1/2 for the major existing solvents shown in the examples described later have been published.

The SP value of a dispersant can be experimentally determined from the boundary between solubility and insolubility when the dispersant is dissolved in various solvents with known SP values. For example, it can be determined by dissolving 1 mL of dispersant in 10 mL of various solvents with different SP values at room temperature under stirrer stirring for 1 hour; the SP value can then be determined by whether the entire amount dissolves. For instance, if a dispersant is soluble in diethyl ether, its SP value will be 7.25 or higher.

As a dispersant (especially an amphiphilic molecule), one having a higher boiling point than water is preferred, and one having a higher boiling point than the melting point of the resin is more preferable from the viewpoint of uniformly dispersing the cellulose fibers in the resin during melt-kneading. Note that a boiling point higher than water refers to a boiling point higher than the boiling point at each pressure on the water vapor pressure curve (for example, 100°C at 1 atmosphere).

By selecting a dispersant with a higher boiling point than water, for example, in a process of obtaining a dried cellulose fiber by drying a slurry containing water as a liquid medium in the presence of a dispersant, the water is replaced by the dispersant during the evaporation process, resulting in the dispersant being present on the surface of the cellulose fibers. This significantly suppresses the aggregation of cellulose fibers.

Furthermore, the method of adding the dispersant is not limited.
A method for producing a dried cellulose fiber by mixing a dispersant with the cellulose fibers after the drying process,
A method for producing a dried cellulose fiber, comprising adding a dispersant to a slurry in which cellulose fibers are dispersed in a liquid medium, and then drying it to obtain a dried cellulose fiber.
A method for manufacturing a resin composite, comprising pre-mixing and melt-kneading a resin, a dried cellulose fiber or a redispersion liquid obtained by dispersing the same in a liquid medium, and a dispersant, followed by molding.
In the production of resin composites, a dispersant is added to the resin in advance, pre-mixed if necessary, then a dried cellulose fiber or a redispersion liquid obtained by dispersing it in a liquid medium is added, and the mixture is melt-kneaded and molded.
These are some examples.

The amount of dispersant is preferably 5 to 100 parts by mass per 100 parts by mass of cellulose fibers, more preferably 10 to 70 parts by mass, and most preferably 20 to 50 parts by mass, from the viewpoint of uniformly dispersing the cellulose fibers in the resin composite.

In one embodiment, the content of the dispersant in the resin composite is preferably 0.3% by mass or more, or 0.5% by mass or more, or 1.0% by mass or more, and preferably 10.0% by mass or less, or 5.0% by mass or less, or 3.0% by mass or less.

In resin composites, the amount of dispersant can be easily determined by a method common to those skilled in the art. While the method is not limited, the following is an example: Using fragments of the resin composite, dissolve the fragments in a solvent that dissolves the resin, and separate the soluble component 1 (resin and dispersant) from the insoluble component 1 (cellulose fibers and dispersant). Reprecipitate soluble component 1 in a solvent that does not dissolve the resin but dissolves the dispersant, separating it into insoluble component 2 (resin) and soluble component 2 (dispersant). Furthermore, dissolve insoluble component 1 in a dispersant-soluble solvent, separating it into soluble component 3 (dispersant) and insoluble component 3 (cellulose fibers). The dispersant can be quantified by concentrating soluble component 2 and soluble component 3 (drying, air drying, vacuum drying, etc.). The concentrated dispersant can then be identified and its molecular weight measured using the method described above.

≪Method for producing dried cellulose fibers≫
One aspect of the present invention also provides a method for producing a cellulose fiber dry body according to the present disclosure. The method includes a slurry preparation step of preparing a slurry containing cellulose fibers and an aqueous medium, and a drying step of drying the slurry to form a cellulose fiber dry body.

(Slurry preparation process)
In this step, a slurry containing cellulose fibers and a liquid medium is prepared. The aforementioned water-miscible organic solvent can be suitably used as the liquid medium. From the viewpoint of process efficiency in the subsequent drying step, the concentration of cellulose fibers in the slurry is preferably 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 avoiding excessive increase in slurry viscosity and solidification due to aggregation, and maintaining good handling properties, it 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. For example, cellulose nanofibers are often produced in dilute dispersions, but the concentration of cellulose fibers in the slurry may be adjusted to the above preferred range by concentrating such dilute dispersions. Methods such as suction filtration, pressure filtration, centrifugal deliquidation, and heating can be used for concentration.

(drying process)
In this process, the slurry is dried under controlled drying conditions to form a cellulose fiber dry product. If the cellulose fiber dry product contains cellulose fibers and additional components, these additional components may be added before, during, and/or after drying the cellulose fiber slurry. For drying, a drying apparatus that enables the above drying rate, such as a spray dryer or extruder, can be used. The drying apparatus may be commercially available, for example, a micro-mist spray dryer (manufactured by Fujisaki Electric Co., Ltd.), a spray dryer (manufactured by Okawara Chemical Machinery Co., Ltd.), or a twin-screw extruder (manufactured by Japan Steel Works, Ltd.). Among the drying conditions, controlling the drying rate, drying temperature, and/or pressure (degree of reduced pressure), especially the drying rate, is useful for producing the cellulose fiber dry product of this disclosure.

The drying rate, which is the amount of liquid medium (parts by mass) removed per minute per 100 parts by mass of slurry, may be, for example, 10%/min or more, 50%/min or more, or 100%/min or more, from the viewpoint of rapidly drying the slurry to form a cellulose fiber dry body of a desired particle size, and may be, for example, 10,000%/min or less, 1,000%/min or less, or 500%/min or less, from the viewpoint of avoiding excessive pulverization of the cellulose fibers, thereby suppressing aggregation of the cellulose fibers and obtaining good handling properties. The drying rate is given by the following formula:
Drying rate (%/min) = (Moisture content of slurry at the start of drying (mass%) - Moisture content of the dried product at the end of drying (mass%)) / Time taken from the start of drying to the end of drying (minutes)
This is the value obtained according to (i.e., the average value throughout the drying process).
Here, "start of drying" refers to the point at which the slurry or cake to be dried is supplied to the apparatus and the drying process begins at the desired drying temperature, reduced pressure, and shear rate. The time spent pre-mixing under conditions different from the drying process (drying temperature, reduced pressure, and shear rate) is not included in the drying time.
Furthermore, the drying endpoint is defined as the point at which the moisture content first falls below 7% by mass, based on sampling taken at intervals of no more than 10 minutes from the start of drying.
In the case of a continuous drying apparatus, the time required from the start of drying to the end of drying can be interpreted as the residence time. In the case of a spray dryer, the residence time can be calculated from the heating air volume and the volume of the drying chamber. Furthermore, when an extruder is used as a drying apparatus, the residence time can be calculated from the screw rotation speed and the total number of screw pitches.

The drying temperature may be, for example, 20°C or higher, 30°C or higher, 40°C or higher, or 50°C or higher, from the viewpoint of drying efficiency and appropriately agglomerating the cellulose fibers to form a cellulose fiber dry body of a desired particle size, and may be, for example, 200°C or lower, 150°C or lower, 140°C or lower, 130°C or lower, or 100°C or lower, from the viewpoint of making it less likely for the cellulose fibers and additional components to undergo thermal degradation and avoiding excessive pulverization of the cellulose fibers.
The drying temperature is the temperature of the heat source in contact with the slurry, and is defined, for example, by the surface temperature of the temperature-controlled jacket of the drying apparatus, the surface temperature of the heating cylinder, or the temperature of the hot air.

The degree of reduced pressure may be -1 kPa or less, -10 kPa or less, -20 kPa or less, -30 kPa or less, -40 kPa or less, or -50 kPa or less, from the viewpoint of drying efficiency and appropriately agglomerating the cellulose fibers to form a cellulose fiber dry product of a desired particle size. From the viewpoint of avoiding excessive pulverization of the cellulose fibers, it may be -100 kPa or more, -95 kPa or more, or -90 kPa or more.

In the drying process, the residence time at a slurry temperature of 20°C to 200°C is preferably set to 0.01 minutes to 10 minutes, 0.05 minutes to 5 minutes, or 0.1 minutes to 2 minutes. Drying under these conditions rapidly dries the cellulose fibers, resulting in the successful production of a cellulose fiber dry product with the desired particle size.

For example, when using a spray dryer, the slurry is sprayed into a drying chamber through which hot gas is circulated using a spray mechanism (rotating disc, pressurized nozzle, etc.) for drying. The slurry droplet size at the time of spray introduction may be, for example, 0.01 μm to 500 μm, 0.1 μm to 100 μm, or 0.5 μm to 10 μm. The hot gas may be an inert gas such as nitrogen or argon, or air. The hot gas temperature may be, for example, 50°C to 300°C, 80°C to 250°C, or 100°C to 200°C. Contact between the slurry droplets and the hot gas in the drying chamber may be parallel flow, counterflow, or parallel-counterflow. The particulate cellulose fiber dry material generated by the drying of the droplets is collected using a cyclone, drum, etc.

Furthermore, for example, when using an extruder, the slurry is introduced from a hopper into a kneading section equipped with a screw, and the slurry is dried by continuously transporting it by the screw within the kneading section under reduced pressure and/or heating. The screw configuration may consist of a transport screw, a counterclockwise screw, and a kneading disc, combined in any order. The drying temperature may be, for example, 50°C to 300°C, 80°C to 250°C, or 100°C to 200°C.

≪Method for manufacturing resin composites≫
One aspect of the present invention provides a method for producing a resin composite comprising cellulose fibers and a resin. The method includes mixing the cellulose fiber dry body of the present disclosure as described above with a resin.

<Resin>
Thermoplastic resins, thermosetting resins, and photocurable resins can be used as the resin. The resin may also be an elastomer. From the viewpoint of moldability and productivity, thermoplastic resins are more preferred.

(thermoplastic resin)
When the resin is a thermoplastic resin, the melting point of the thermoplastic resin may be appropriately selected depending on the application of the resin composite. Examples of thermoplastic resin melting points include 150°C to 190°C or 160°C to 180°C for resins with relatively low melting points (e.g., polyolefin resins), and 220°C to 350°C or 230°C to 320°C for resins with relatively high melting points (e.g., polyamide resins).

The thermoplastic resin can preferably be at least one selected from the group consisting of polyolefin resins, polyacetate resins, polycarbonate resins, polyamide resins, polyester resins, polyphenylene ether resins, and acrylic resins.

Preferred polyolefin resins as thermoplastic resins are polymers obtained by polymerizing olefins (e.g., α-olefins) and/or alkenes as monomer units. Specific examples of polyolefin resins include ethylene-based (co)polymers such as low-density polyethylene (e.g., linear low-density polyethylene), high-density polyethylene, ultra-low-density polyethylene, and ultra-high molecular weight polyethylene; polypropylene-based (co)polymers such as polypropylene, ethylene-propylene copolymer, and ethylene-propylene-diene copolymer; and copolymers of ethylene and α-olefins, such as ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer, and ethylene-glycidyl methacrylate copolymer.

The most preferred polyolefin resin here is polypropylene. In particular, polypropylene with a melt mass flow rate (MFR) of 3 g/10 min or more and 30 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 the MFR is more preferably 5 g/10 min, even more preferably 6 g/10 min, and most preferably 8 g/10 min. The upper limit is more preferably 25 g/10 min, even more preferably 20 g/10 min, and most preferably 18 g/10 min. From the viewpoint of improving the toughness of the resin composite, it is desirable that the MFR does not exceed the upper limit, and from the viewpoint of the fluidity of the resin composite, it is desirable that it does not exceed the lower limit.

Furthermore, to enhance affinity with cellulose fibers, acid-modified polyolefin resins can also be suitably used. Mono- or polycarboxylic acids can be used as the acid for acid modification; examples include maleic acid, fumaric acid, succinic acid, phthalic acid and their anhydrides, as well as citric acid. Maleic acid or its anhydride is particularly preferred due to its ease of increasing the modification rate. While there are no particular restrictions on the modification method, a common method involves heating the polyolefin resin above its melting point in the presence or absence of a peroxide and then melt-kneading it. All of the aforementioned polyolefin resins can be used for acid modification, but polypropylene is particularly preferred. Acid-modified polypropylene resin may be used alone, but it is more preferable to mix it with unmodified polypropylene resin to adjust the overall modification rate of the resin. In this case, the ratio of acid-modified polypropylene resin to the total polypropylene resin is preferably 0.5% to 50% by mass. A more preferable lower limit is 1% by mass, 2% by mass, 3% by mass, 4% by mass, or 5% by mass. A more preferable upper limit is 45% by mass, 40% by mass, 35% by mass, 30% by mass, or 20% by mass. To maintain the interfacial strength between the resin and the cellulose fibers, a value above the lower limit is preferable, while to maintain the ductility of the resin, a value below the upper limit is preferable.

The melt mass flow rate (MFR) of acid-modified polypropylene resin, measured at 230°C and under a load of 21.2 N in accordance with ISO 1133, is preferably 50 g/10 min or more, or 100 g/10 min or more, or 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 cellulose fibers. While there is no particular upper limit, it is preferably 500 g/10 min to maintain mechanical strength.

Preferred polyamide resins as thermoplastic resins include: polyamides obtained by polycondensation reactions 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., butanediamine, pentanediamine, hexanediamine) Examples include polyamides obtained as copolymers with heptanediic acid, octanedioic acid, nonanediic acid, decanediic 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. (e.g., 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 obtained by copolymerizing these (e.g., 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 composite, 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, and from the viewpoint of ease of manufacturing the resin composite, the above melting point is preferably 350°C or lower, or 320°C or lower, or 300°C or lower.

There are no particular restrictions on the concentration of terminal carboxyl groups in 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 polyamide resins, the ratio of carboxyl end groups to total end groups ([COOH]/[total end groups]) is preferably 0.30 or higher, 0.35 or higher, 0.40 or higher, or 0.45 or higher, from the viewpoint of dispersibility of cellulose fibers in the resin composite, and preferably 0.95 or lower, 0.90 or lower, 0.85 or lower, or 0.80 or lower, from the viewpoint of the color tone of the resin composite.

The end group concentration of polyamide resins can be adjusted by known methods. One such method involves adding an end group adjusting agent (e.g., diamine compounds, monoamine compounds, dicarboxylic acid compounds, monocarboxylic acid compounds, acid anhydrides, monoisocyanates, monoacid halides, monoesters, monoalcohols, etc.) to the polymerization solution during the polymerization of the polyamide, so that a predetermined end group concentration is achieved.

Examples of end-modifying agents 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 several of these arbitrarily selected. Among these, from the viewpoint of reactivity, stability of the encapsulated end, and cost, one or more end-modifying agents 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 are preferred, with acetic acid being the most preferred.

Examples of end modifiers 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 end modifiers 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 sealing end, and cost.

The concentrations of amino-terminated and carboxyl-terminated groups in polyamide resins can be determined by ^1H -NMR from the integrated values of characteristic signals corresponding to each terminus. This method is preferred in terms of accuracy and simplicity. More specifically, it is recommended to use the method described in Japanese Patent Publication No. 7-228775, using deuterated trifluoroacetic acid as the measurement solvent and performing 300 or more scans for integration.

The intrinsic viscosity [η] of polyamide resins, measured under conditions of 30°C in concentrated sulfuric acid, is preferably 0.6 to 2.0 dL/g, 0.7 to 1.4 dL/g, 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 composite is, for example, injection molded. In this disclosure, "intrinsic viscosity" is synonymous with viscosity generally called intrinsic viscosity. The intrinsic viscosity is determined by measuring the ηsp/c of several measurement solvents of different concentrations under conditions of 30°C in 96% concentrated sulfuric acid, deriving a relationship between each ηsp/c and concentration (c), and extrapolating the concentration to zero. This extrapolated value is the intrinsic viscosity. Details of the above method are described, for example, on pages 291-294 of Polymer Process Engineering (Prentice-Hall, Inc. 1994). From the standpoint of accuracy, it is desirable to use at least four different concentrations of the measurement solvent (e.g., 0.05 g/dL, 0.1 g/dL, 0.2 g/dL, 0.4 g/dL).

As a thermoplastic resin, one or more polyester resins 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 these, PET, PBS, PBSA, PBT, and PEN are more preferred, and PBS, PBSA, and PBT are particularly preferred.

The end groups of the polyester resin can be arbitrarily changed by the monomer ratio during polymerization, the presence or absence and amount of end stabilizers added, etc. The ratio of carboxyl end groups to the total end groups of the polyester resin ([COOH]/[total end groups]) is preferably 0.30 or higher, or 0.35 or higher, or 0.40 or higher, or 0.45 or higher, from the viewpoint of dispersibility of cellulose fibers in the resin composite, and preferably 0.95 or lower, or 0.90 or lower, or 0.85 or lower, or 0.80 or lower, from the viewpoint of the color tone of the resin composite.

As thermoplastic resins, preferred polyacetal resins generally include homopolyacetals derived from formaldehyde and copolyacetals with trioxane as the main monomer and 1,3-dioxolane as a comonomer component. Both are usable, but copolyacetals are preferred from the viewpoint of thermal stability during processing. The amount of structure derived from the comonomer component (e.g., 1,3-dioxolane) is preferably 0.01 mol% or more, 0.05 mol% or more, 0.1 mol% or more, or 0.2 mol% or more, from the viewpoint of thermal stability during extrusion and molding processes. From the viewpoint of mechanical strength, it is preferably 4.0 mol% or less, 3.5 mol% or less, 3.0 mol% or less, 2.5 mol% or less, or 2.3 mol% or less.

(thermosetting resin)
Examples of thermosetting resins include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol E type epoxy resin, bisphenol M type epoxy resin, bisphenol P type epoxy resin, and bisphenol Z type epoxy resin; novolac type epoxy resins such as bisphenol A novolac type epoxy resin, phenol novolac type epoxy resin, and cresol novolac epoxy resin; biphenyl type epoxy resin, biphenyl aralkyl type epoxy resin, and arylalkyl epoxy resins. Epoxy resins of the tetraphenyloleethane type, naphthalene type, anthracene type, phenoxy type, dicyclopentadiene type, norbornene type, adamantane type, fluorene type, glycidyl methacrylate copolymer epoxy resins, copolymer epoxy resins of cyclohexylmaleimide and glycidyl methacrylate, epoxy-modified polybutadiene rubber derivatives, CTBN-modified epoxy resins, trimethylolpropane polyglycidyl ether, Phenyl-1,3-diglycidyl ether, biphenyl-4,4'-diglycidyl ether, 1,6-hexanediol diglycidyl ether, ethylene glycol or propylene glycol diglycidyl ether, sorbitol polyglycidyl ether, tris(2,3-epoxypropyl) isocyanurate, triglycidyl tris(2-hydroxyethyl) isocyanurate, phenol novolac resin, cresol novolac resin, bisphenol A novolac resin and other novolac-type phenolic resins, unmodified resol phenolic resin, paulownia Examples include phenolic resins such as oil-modified resol phenolic resins modified with oil, linseed oil, walnut oil, etc., phenoxy resins, urea resins, triazine ring-containing resins such as melamine resins, unsaturated polyester resins, bismaleimide resins, diallyl phthalate resins, silicone resins, resins having a benzoxazine ring, norbornene-based resins, cyanate resins, isocyanate resins, urethane resins, benzocyclobutene resins, maleimide resins, bismaleimide triazine resins, polyazomethine resins, and thermosetting polyimides.

(photocurable resin)
Examples of photocurable resins include (meth)acrylate resins, vinyl resins, and epoxy resins. These are generally classified into two types based on their reaction mechanism: radical reaction types, where monomers react to radicals generated by light, and cationic reaction types, where monomers undergo cationic polymerization. Monomers used in radical reaction types include (meth)acrylate compounds and vinyl compounds (e.g., certain vinyl ethers). Examples of cationic reaction types include epoxy compounds and certain vinyl ethers. For example, epoxy compounds that can be used as cationic reaction types can be monomers for both thermosetting and photocurable resins.

(Meth)acrylate compounds are compounds that have one or more (meth)acrylate groups in their molecule. Examples of (meth)acrylate compounds include monofunctional (meth)acrylates, polyfunctional (meth)acrylates, epoxy acrylates, polyester acrylates, and urethane acrylates.

Examples of vinyl compounds include vinyl ethers, styrene, and styrene derivatives. Examples of vinyl ethers include ethyl vinyl ether, propyl vinyl ether, hydroxyethyl vinyl ether, and ethylene glycol divinyl ether. Examples of styrene derivatives include methylstyrene and ethyl styrene. Other vinyl compounds include triallyl isocyanurate and trimaallyl isocyanurate.

As a raw material for photocurable resins, so-called reactive oligomers may be used. Examples of reactive oligomers include oligomers that possess any combination selected from (meth)acrylate groups, epoxy groups, urethane bonds, and ester bonds within the same molecule. These include, for example, urethane acrylate possessing both (meth)acrylate groups and urethane bonds within the same molecule, polyester acrylate possessing both (meth)acrylate groups and ester bonds within the same molecule, and epoxy acrylate derived from epoxy resins possessing both epoxy groups and (meth)acrylate groups within the same molecule.

(Elastomer)
Examples of elastomers (i.e., rubbers) include natural rubber (NR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR), acrylonitrile-styrene-butadiene copolymer rubber, chloroprene rubber, styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber, chlorosulfonated polyethylene rubber, modified natural rubber (epoxidized natural rubber (ENR), hydrogenated natural rubber, deproteinized natural rubber, etc.), ethylene-propylene copolymer rubber, acrylic rubber, epichlorohydrin rubber, polysulfurized rubber, silicone rubber, fluororubber, urethane rubber, and the like.

When the resin is a thermoplastic resin, a resin composite can be produced by melt-kneading cellulose fibers (which may be in the form of a dried body or a redispersed liquid obtained by dispersing them in a dispersion medium) with the thermoplastic resin. A more specific method for producing the resin composite is as follows:
- A method for obtaining a pellet-shaped molded body by mixing resin monomers and cellulose fibers, carrying out a polymerization reaction, extruding the resulting resin composite into strands, and cooling and solidifying it in a water bath.
- A method for obtaining a pellet-shaped molded body by melting and kneading a mixture of resin and cellulose fibers using a single-screw or twin-screw extruder, extruding it into strands, and cooling and solidifying it in a water bath.
- A method of obtaining an extruded molded product by melting and kneading a mixture of resin and cellulose fibers using a single-screw or twin-screw extruder, extruding it into a rod or cylindrical shape, and then cooling it.
- A method of obtaining a molded article in the form of a sheet or film by melting and kneading a mixture of resin and cellulose fibers using a single-screw or twin-screw extruder and extruding it through a T-die.
Examples include the above. In a preferred embodiment, a mixture of resin and cellulose fibers is melt-kneaded using a single-screw or twin-screw extruder, extruded into strands, and cooled and solidified in a water bath to obtain a pellet-shaped molded body.
A specific example of a method for melt-kneading resin and cellulose fibers is a method in which the resin and cellulose fibers, which have been transported in a desired ratio, are mixed, and then melt-kneaded.

For melt kneading, extruders such as single-screw extruders and twin-screw extruders can be used, but twin-screw extruders are preferred for controlling the dispersibility of cellulose fibers. The L/D ratio, obtained by dividing the extruder's cylinder length (L) by the screw diameter (D), is preferably 30 or more, and particularly preferably 40 or more. Furthermore, the screw rotation speed during kneading is preferably in the range of 50 to 800 rpm, and more preferably in the range of 100 to 600 rpm.

Each screw within the extruder cylinder is optimized by combining elements such as an elliptical, two-bladed screw-shaped conveying screw and a kneading disc, which is a mixing element.

When the resin is a thermoplastic resin, the minimum processing temperatures recommended by thermoplastic resin suppliers are 255-270°C for nylon 66, 225-240°C for nylon 6, 170-190°C for polyacetal resin, and 160-180°C for polypropylene. The heating setting temperature is preferably within a range of 20°C higher than these recommended minimum processing temperatures. By setting the mixing temperature within this range, the cellulose fibers and resin can be uniformly mixed.

Resin composites containing thermoplastic resins can be provided in various shapes. Specifically, these include resin pellets, sheets, fibers, plates, and rods. However, resin pellets are preferred due to their ease of post-processing and transportation. Preferred pellet shapes include round, oval, and cylindrical, depending on the extrusion cutting method. Pellets cut using an underwater cutting method are often round, those cut using a hot cutting method are often round or oval, and those cut using a strand cutting method are often cylindrical. For round pellets, the preferred size is a pellet diameter of 1 mm to 3 mm. For cylindrical pellets, the preferred diameter is 1 mm to 3 mm, and the preferred length is 2 mm to 10 mm. From the viewpoint of operational stability during extrusion, the diameter and length should be above the lower limit, and from the viewpoint of ease of engagement with the molding machine during post-processing, they should be below the upper limit.

Resin composites containing thermoplastic resins can be used as various resin molded articles. There are no particular restrictions on the manufacturing method of the resin molded articles; any method is acceptable, but injection molding, extrusion molding, blow molding, inflation molding, and foam molding are all usable. Among these, injection molding is the most preferred method from the standpoint of design and cost.

When the resin is a thermosetting or photocurable resin, the resin composite can be produced by, for example, thoroughly dispersing cellulose fibers in a resin solution or resin powder dispersion and drying it; thoroughly dispersing cellulose fibers in a resin monomer liquid and polymerizing them using heat, UV irradiation, polymerization initiators, etc.; thoroughly impregnating a dried cellulose fiber body with a resin solution or resin powder dispersion and drying it; or thoroughly impregnating a dried cellulose fiber body with a resin monomer liquid and polymerizing it using heat, UV irradiation, polymerization initiators, etc. Various polymerization initiators, curing agents, curing accelerators, polymerization inhibitors, etc., can be added during curing.

When the resin is a thermosetting or photocuring resin, a method may be used in which an uncured or semi-cured sheet called a prepreg is prepared, and then the prepreg is layered in single or laminated layers and cured and molded by pressurization and heating. Examples of pressurization and heating methods include press molding, autoclave molding, bagging molding, wrapping tape method, and internal pressure molding.

If the resin is a photocurable resin, resin composites can be manufactured using various curing methods that utilize active energy rays.

When the resin is an elastomer, the resin composite can be manufactured by methods such as dry kneading of dried cellulose fibers and raw rubber, or by dispersing or dissolving the cellulose fibers and raw rubber in a dispersion medium, followed by drying and mixing. Homogenizer mixing is preferred as a mixing method because it can promote dispersion by applying high shear force and pressure. However, other methods such as propeller-type agitators, rotary agitators, electromagnetic agitators, and manual agitation can also be used. The resin composite containing the elastomer can be molded using desired molding methods such as die molding, injection molding, extrusion molding, hollow molding, and foam molding to obtain unvulcanized molded articles in desired shapes such as sheets, pellets, and powders. The unvulcanized molded articles can be vulcanized by heat treatment or other methods as needed to obtain the resin composite.

A resin composite containing a thermoplastic resin or elastomer may be partially (for example, several locations) heat-treated to melt it and then used by bonding it to a substrate, such as a resin or metal. Alternatively, the resin composite may be a coating applied to a resin or metal substrate, or it may form a laminate with the substrate. Furthermore, sheet-like, film-like, or fibrous resin composites may undergo secondary processing such as annealing, etching, corona treatment, plasma treatment, texture transfer, cutting, and surface polishing.

In a resin composite, the amount of cellulose fibers per 100 parts by mass of resin is preferably 0.001 parts by mass or more, or 0.01 parts by mass or more, or 0.1 parts by mass or more, or 1 part by mass or more, from the viewpoint of balancing processability and mechanical properties, and preferably 100 parts by mass or less, or 80 parts by mass or less, or 70 parts by mass or less, or 50 parts by mass or less.

The tensile elongation at break of the resin composite may, in one embodiment, be 5% or more, 8% or more, or 10% or more. From the viewpoint of ease of manufacturing the resin composite, the tensile elongation at break may, in one embodiment, be 200% or less, 100% or less, or 50% or less.

The present invention will be further described based on examples, but the present invention is not limited to these examples.

Manufacturing of cellulose fiber slurry
[CNF-A]
Commercially available Celish KY100G (manufactured by Daicel Finechem) was used as the CNF-A cake.

[CNF-B] (acetylated CNF)
One part by mass of cotton linter pulp was stirred at 500 rpm for 1 hour at room temperature using a single-screw agitator (IMEX DKV-1 φ125 mm dissolver) in 30 parts by mass of dimethyl sulfoxide (DMSO). Subsequently, the mixture was fed into a bead mill (IMEX NVM-1.5) using a hose pump and circulated with DMSO alone for 180 minutes to obtain a fine cellulose fiber slurry, slurry S1 (DMSO solvent), with a solid content of 3.2% by mass.

During circulating operation, the bead mill rotation speed was set to 2500 rpm and the peripheral speed to 12 m/s. The beads used were zirconia, φ2.0 mm in diameter, with a packing density of 70% (the slit gap in the bead mill was 0.6 mm). Furthermore, during circulating operation, the slurry temperature was controlled to 40°C using a chiller to absorb heat generated by friction.

After adding slurry S1 to an explosion-proof disperser tank, 3.2 parts by mass of vinyl acetate and 0.49 parts by mass of sodium bicarbonate were added. The tank temperature was set to 50°C, and the mixture was stirred for 120 minutes to obtain a slurry (DMSO solvent) with a solid content of 2.9% by mass.

To stop the reaction, 30 parts by mass of pure water were added and thoroughly stirred, then the mixture was concentrated in a dehydrator. The resulting wet cake was dispersed in 30 parts by mass of pure water, stirred, and concentrated. This washing operation was repeated a total of five times to remove unreacted reagents and solvents, yielding 10 parts by mass of acetylated fine cellulose fiber cake (CNF-B cake) (water solvent) with a solid content of 10% by mass. A porous sheet was prepared from this cake, and the degree of acyl substitution (DS) was determined to be DS = 1.0.

[CNF-C] (CNF processed with a discriminator)
Three parts by mass of cotton linter pulp were immersed in 27 parts by mass of water and heat-treated in an autoclave at 130°C for 4 hours. The resulting swollen pulp was washed with water to obtain purified pulp containing water (30 parts by mass). Next, 170 parts by mass of water were added to 30 parts by mass of the purified pulp containing water and dispersed in water (solid content 1.5% by mass). Using an SDR14 type laboratory refiner (pressure type disc type) manufactured by Aikawa Iron Works Co., Ltd. as a disc refiner, the aqueous dispersion was beaten for 20 minutes with a clearance of 1 mm between the discs. Then, it was concentrated to a solid content of 10% by mass using a dewatering machine to obtain CNF-C cake (aqueous solvent).

[CNF-D] (CNF-C that has been further processed using a high-pressure homogenizer to remove fibrous fibers)
The CNF-C cake was thoroughly beaten under conditions that reduced the clearance to almost zero, yielding a beaten aqueous dispersion (solid content concentration: 1.5% by mass). The obtained beaten aqueous dispersion was then subjected to 15 micronization processes using a high-pressure homogenizer (NSO15H, manufactured by Nilo Soavi, Italy) at an operating pressure of 100 MPa to obtain a cellulose fiber slurry (solid content concentration: 1.5% by mass). This slurry was then concentrated to a solid content of 10% by mass using a dewatering machine to obtain the CNF-D cake (aqueous solvent).

[CNF-E] (acetylated CNF)
The preparation was carried out in the same manner as CNF-B, except that the reaction time was set to 60 minutes. A porous sheet was prepared from this cake, and the degree of acyl substitution (DS) was determined to be DS = 0.5.

<Resin>
Polyamide 6 (manufactured by Ube Industries: 1013B)

<Dispersant>
Polyethylene oxide-polypropylene oxide copolymer (PEG-PPG) (manufactured by Sanyo Chemical Industries: GL-3000)

Manufacturing of dried cellulose fibers
To a cellulose fiber cake (10% solids), a dispersant was added in an amount of 43 parts by mass per 100 parts by mass of cellulose solids, and the mixture was thoroughly stirred to obtain a cellulose fiber cake containing the dispersant (except for MMSD described later). Alternatively, a cellulose fiber cake (10% solids) was diluted with distilled water to a solids content of 1%, and then a dispersant was added in an amount of 43 parts by mass per 100 parts by mass of cellulose solids, and the mixture was thoroughly stirred to obtain a cellulose fiber slurry (except for MMSD described later). These were then put into a drying apparatus as raw materials and dried at a predetermined shear rate, reduced pressure, and heating temperature (jacket temperature or hot air temperature). The moisture content was measured using an infrared heating type moisture meter (MX-50 (manufactured by A&D)), and the time when the moisture content was 7% by mass or less (solids content of 93% or more) was defined as the end of the drying process. The conditions were as follows.

[Redigeg mixer (LM)]
Equipment: Rediger mixer manufactured by Chuo Kiko Co., Ltd. (Model number: VT-20)
Conditions: The jacket temperature was 100°C. The mixture was stirred using an agitator (peripheral speed 1 m/s) and a chopper (3000 rpm) while the pressure was reduced to -90 kPa using a vacuum pump. Vacuum drying was carried out until the product temperature reached 50°C.
For clearance, we measured the minimum distance between the chopper (100 mm in diameter) and the jacket.
The drying time under these conditions was 160 minutes.
The drying temperature was calculated by taking the average of three surface temperature measurements of the jacket.

[High-Speed Vacuum Dryer (HSVD)]
Equipment: Earth Technica Co., Ltd. High-speed vacuum dryer (model number: FS10)
Conditions: The jacket temperature was 70°C. The mixture was stirred using an agitator (peripheral speed 2 m/s) and a chopper (3500 rpm) while the pressure was reduced to -70 kPa using a vacuum pump. Vacuum drying was carried out until the product temperature reached 60°C.
For clearance, we measured the minimum distance between the chopper (100 mm in diameter) and the agitator.
The drying time under these conditions was 180 minutes.
The drying temperature was calculated by taking the average of three surface temperature measurements of the jacket.

[FM Mixer (HM)]
Equipment: FM mixer manufactured by Nippon Coke Industries Co., Ltd. (Model number: FM20)
Conditions: The jacket temperature was 80°C, and the pressure was reduced to -70 kPa using a vacuum pump while stirring with an agitator (500 rpm). Vacuum drying was performed until the product temperature reached 70°C.
For clearance, the minimum distance between the upper stirring blade (400 mm in diameter) and the jacket was measured.
The drying time under these conditions was 180 minutes.
The drying temperature was calculated by taking the average of three surface temperature measurements of the jacket.

[Paddle Dryer (PD)]
Equipment: Paddle dryer manufactured by Nara Machine Works Co., Ltd. (Model number: NPD-1.6W-12L)
Conditions: The product was dried at a heating steam temperature of 120°C while being stirred with an agitator (30 rpm) until the product temperature reached 100°C.
For clearance, the minimum distance between the stirring blade (250 mm in diameter) and the jacket was measured.
The drying time under these conditions was 50 minutes.
The drying temperature was determined by taking the average of three surface temperatures of the stirring blade through which heated steam was passed.

[Micro Mist Spray Dryer (MMSD)]
Equipment: Micro-mist spray dryer manufactured by Fujisaki Electric Co., Ltd. (Model number: MDL050-M)
Conditions: A cellulose fiber slurry was dried at an inlet temperature of 200°C, an air supply volume of 1 ^m³ /min, a nozzle air flow rate of 80 NL/min, and a slurry flow rate of 50 mL/min. The dried powder was then collected using a cyclone-type recovery system.
Since this device does not have a stirring mechanism, shear rate is considered to be virtually nonexistent.
Under these conditions, the drying time and residence time were 1 minute.
The drying temperature was determined by taking the average of three measurements of the hot air inlet temperature during the drying process.

[Twin screw extruder (Ex-dry)]
Equipment: Twin-screw extruder manufactured by Japan Steel Works Ltd. (Model number: TEX54αIII: L/D = 63)
Conditions: The cylinder temperature was 200°C, and the screw was rotated at 66 rpm while the raw material was supplied to the uppermost barrel at a rate of 20 kg/h using a gravitational feeder, and dried powder was obtained from the discharge port.
For clearance, the minimum distance between the kneading disc (54 mm in diameter) and the cylinder was measured.
Under these conditions, the drying time and residence time were 1 minute.
The drying temperature was determined by taking three measurements of the temperature of the cylinder where the downstream kneading disc is located and using the average value.

[Planetary Mixer (PM)]
Equipment: Planetary mixer manufactured by Kodaira Seisakusho Co., Ltd. (Model number: ACM-5LVT: Hook type)
Conditions: The jacket temperature was 60°C, and the pressure was reduced to -90 kPa using a vacuum pump while stirring at 307 rpm. Vacuum drying was carried out until the product temperature reached 50°C.
For clearance, we measured the minimum distance between the hook feather (100 mm in diameter) and the jacket.
The drying time under these conditions was 180 minutes.
The drying temperature was calculated by taking the average of three surface temperature measurements of the jacket.

[Examples 1-12, Comparative Example 8]
Using the CNF shown in Table 1 and the apparatus as shown in Table 2, a dried cellulose fiber was obtained using the CNF, drying temperature, and shear rate as shown in Tables 3 and 4. In Example 12, a cellulose fiber slurry was obtained without using a dispersant in the preparation of the raw materials.

Manufacturing of resin composites
The cellulose fiber dried material produced as described above and a thermoplastic resin (UBE Nylon 1013B, manufactured by Ube Industries, Ltd.) were blended in such a ratio that the cellulose fibers constituted 10% by mass of the resin composite, and a resin composite was produced according to the following procedure.

[Extruder Configuration]
In a twin-screw extruder (STEER OMEGA30H, L/D=60) with 13 cylinder blocks, cylinder 1 was water-cooled, cylinder 2 was set to 80°C, cylinder 3 to 150°C, and cylinders 4 through the die to 250°C.

The screw configuration consists of cylinders 1-3 as a conveying zone composed solely of conveying screws. Cylinder 4 has two clockwise kneading discs (feed-type kneading discs; hereinafter sometimes simply referred to as RKD) and two neutral kneading discs (non-conveying type kneading discs; hereinafter sometimes simply referred to as NKD) arranged sequentially from the upstream side. Cylinder 5 is a conveying zone, with one RKD and two subsequent NKDs in cylinder 6. Cylinders 7 and 8 are conveying zones, with two NKDs in cylinder 9. Cylinder 10 is a conveying zone, with two NKDs and one subsequent counterclockwise screw in cylinder 11. Cylinders 12 and 13 are conveying zones. A vent port is installed at the top of cylinder 12 to allow for reduced pressure suction, and vacuum suction was performed.

Cellulose fiber dry material and thermoplastic resin were mixed and melt-kneaded using a twin-screw extruder at a rotation speed of 250 rpm to extrude into strands. The mixture was then water-cooled and cut to obtain pellets. The obtained pellets were melted at 260°C using an attached injection molding machine to prepare dumbbell-shaped test specimens according to JIS K7127 standard, which were used for evaluation.

≪Rating≫
<Evaluation of Cellulose Fibers>
[Fabrication of porous sheets]
First, the wet cake was added to tert-butanol and then dispersed using a mixer or similar device until no aggregates remained. The concentration was adjusted to 0.5% by mass for every 0.5 g of cellulose fiber solids. 100 g of the resulting tert-butanol dispersion was filtered on filter paper, dried at 150°C, and then the filter paper was peeled off to obtain a sheet. Sheets with an air permeability resistance of 100 sec/100 ml or less per 10 g/ ^m² of sheet basis were selected as porous sheets and used as measurement samples.
After measuring the basis weight W (g/ ^m² ) of the sample, which had been left standing for one day in an environment of 23°C and 50% RH, the air permeability resistance R (sec/100ml) was measured using a Wangyan-type air permeability resistance tester (manufactured by Asahi Seiko Co., Ltd., model EG01). At this time, the value per 10 g/ ^m² basis weight was calculated according to the following formula.
Air permeability resistance per 10 g/ ^m² (sec/100 ml) = R/W × 10

[Degree of acyl substitution (DS)]
Infrared spectral measurements were taken at five locations on a porous sheet using the ATR-IR method with a Fourier transform infrared spectrophotometer (JASCO FT/IR-6200). The infrared spectral measurements were performed under the following conditions.
Total number of times: 64
Wavenumber resolution: 4cm ^-1 ,
Measurement wavefrequency range: 4000-600 ^cm⁻¹
ATR crystal: diamond,
Incident angle: 45°
The IR index from the obtained IR spectrum is calculated using the following formula (1):
IR Index = H1730/H1030... (1)
The values were calculated according to the following formula. In the formula, H1730 and H1030 are the absorbances at 1730 ^cm⁻¹ and 1030 ^cm⁻¹ (absorption bands for C-O stretching vibrations of the cellulose skeleton chain). However, these values represent the absorbance when the baseline is set to 0, with the baseline being the line connecting 1900 ^cm⁻¹ and 1500 ^cm⁻¹ and the line connecting 800 ^cm⁻¹ and 1500 ^cm⁻¹ , respectively.
Then, the average degree of replacement at each measurement location was calculated from the IR index according to the following formula (2), and the average value was defined as DS.
DS = 4.13 × IR index ... (2)

[Crystallization]
X-ray diffraction measurements were performed on the porous sheet, and the degree of crystallinity was calculated using the following formula.
Crystallinity (%) = [I ₍₂₀₀₎ - I _(amorphous) ] / I ₍₂₀₀₎ × 100
I ₍₂₀₀₎ : Diffraction peak intensity at the 200 plane (2θ = 22.5°) in a cellulose type I crystal. I _(amorphous) : Halo peak intensity due to amorphous material in a cellulose type I crystal, at a peak 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: 40kV
Current 15mA
Starting angle 2θ=5°
Ending angle 2θ = 30°
Sampling width 0.020°
Scan speed: 2.0°/min
Sample: A porous sheet is attached to the sample holder.

[Average fiber diameter]
Cellulose fiber cake or cellulose fiber slurry was diluted to 0.01% by mass with tert-butanol, dispersed using a high-shear homogenizer (IKA, product name "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm for 5 minutes, cast onto mica, and air-dried. The resulting material was then measured using a high-resolution scanning electron microscope. The measurement was performed by adjusting the magnification so that at least 100 cellulose fibers could be observed. The major axis (L) of 100 randomly selected cellulose fibers was measured, and the average of the 100 cellulose fibers was calculated.

[Weight-average molecular weight (Mw), number-average molecular weight (Mn), and Mw/Mn ratio]
0.88 g of porous sheet was weighed, cut into small pieces with scissors, lightly stirred, and then 20 mL of pure water was added and left for 1 day. Next, the water and solids were separated by centrifugation. Then 20 mL of acetone was added, lightly stirred, and left for 1 day. Next, the acetone and solids were separated by centrifugation. Then 20 mL of N,N-dimethylacetamide was added, lightly stirred, and left for 1 day. After separating the N,N-dimethylacetamide and solids again by centrifugation, 20 mL of N,N-dimethylacetamide was added, lightly stirred, and left for 1 day. The 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, stirred with a stirrer, and visually confirmed to be dissolved. The solution containing the dissolved cellulose fibers was filtered through a 0.45 μm filter, and the filtrate was used as a sample for gel permeation chromatography. The equipment and measurement conditions used are as follows.
Equipment: Tosoh Corporation HLC-8120
Column: TSKgel SuperAWM-H (6.0 mm I.D. × 15 cm) × 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 alkali-soluble polysaccharides]
The alkali-soluble polysaccharide content was determined for cellulose fibers by subtracting the α-cellulose content from the holocellulose content (Wise method) using the method described in 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 content was taken as the average alkali-soluble polysaccharide content of the cellulose fibers.

<Evaluation of dried cellulose fibers>
Measurements were performed using a powder tester (model number: PT-X) manufactured by Hosokawa Micron Corporation.

[Angle of repose]
Using a spatula, 100 g of dried cellulose fiber was gently dropped at approximately 10 g/min into the center of a horizontally positioned stainless steel measuring platform with a diameter of 80 mm. The drop was made through a funnel (stainless steel, upper opening diameter 70 mm, lower opening diameter 7 mm, inclination angle 60°) from a height of 110 mm between the lower opening of the funnel and the measuring platform. The dried cellulose fiber was deposited on the measuring platform in a conical shape. A photograph of the cone shape was taken from the side, and the angle between the generatrix of the cone and the horizontal plane was measured. The number average of three measurements was taken as the angle of repose.

[Collapse angle]
For the sample whose angle of repose was measured, a 109g weight was dropped from a height of 160mm onto the same base as the measuring platform three times at 2-second intervals. Then, the conical shape of the sample was photographed from the side, and the angle between the slant height of the cone and the horizontal plane was measured. The number average of the three measurements was defined as the collapse angle.

[Difference angle]
The difference between the angle of repose and the angle of collapse was calculated as the difference angle.

[Loose bulk density]
A 100 mL stainless steel cylindrical container with a closed bottom (inner diameter 50.46 mm x depth 50 mm) was filled with cellulose fiber dry material at a rate of 10 g/min using a spatula until it overflowed. After leveling off the excess material, its weight was measured to the nearest 0.01 g. The number average of three weight measurements was divided by the internal volume of the cylindrical container to calculate the loose bulk density.

[Collection density]
A resin adapter (inner diameter 50.46 mm x length 40 mm) of sufficient capacity was tightly attached to the top of a bottomed cylindrical container similar to the one used for loose bulk density measurement. Following the same procedure as for measuring loose bulk density, the container was filled with cellulose fiber dry material until it overflowed. With the adapter still attached, the bottomed cylindrical container was subjected to vibrations of 1.5 mm amplitude and 50 Hz for 30 seconds using a motor with an eccentric weight attached to the rotating shaft. Subsequently, the adapter was removed, the dry material was leveled off, and its weight was measured to the nearest 0.01 g. The number average of three weight measurements was divided by the internal volume of the bottomed cylindrical container to calculate the bulk density.

[Degree of Compression]
From the above values of bulk density (high and low) and bulk density (low and low), the following formula is used:
The degree of compression was calculated according to the formula: Compression = (Bulk density when compressed - Bulk density when loosened) / Bulk density when compressed.

[Moisture percentage]
Measurements were taken using an infrared heating type moisture meter (MX-50 (manufactured by A&D)).

[Particle size distribution]
A precisely weighed φ100 mm sieve was placed in a precisely weighed φ100 mm receiving container, stacked in the order of mesh sizes 710 μm, 1000 μm, and 1700 μm. A precisely weighed dry cellulose fiber sample weighing between 1 and 20 g was placed on the top sieve, and then vibrations with an amplitude of 1.5 mm and an amplitude of 50 Hz were applied for 10 minutes. Subsequently, the fractionated samples were precisely weighed with the sieves still attached, and the weight fraction of each fraction was calculated to obtain the particle size distribution.

[Screen Mesh Evaluation]
With a 50-mesh screen mesh attached between the die adapter and the die head, the extruder was operated at a discharge rate of 20 kg/h for 1 hour, and the amount of particles captured by the screen mesh was evaluated in the following three stages.
A... Almost no particles were captured. B... Some particles were captured, requiring replacement of the screen mesh. C... Die pressure increased before the end of operation, requiring replacement of the screen mesh.

<Evaluation of resin composites>
[Tensile elongation at break, flexural modulus]
From the obtained pellets, multi-purpose test specimens conforming to ISO 294-3 were formed using an injection molding machine under conditions compliant with JIS K6920-2.
For the multipurpose test specimens, the tensile elongation at break was measured in accordance with ISO 527, and the flexural modulus was measured in accordance with ISO 179. Since polyamide resin undergoes changes due to moisture absorption, the specimens were stored in aluminum moisture-proof bags immediately after molding to suppress moisture absorption.
The results are shown in Table 1.

The high-toughness resin composites provided by this invention can be suitably applied to various resin molded article applications.

Claims (11)

A cellulose fiber dry body comprising unmodified cellulose fibers and a dispersant ,
The cellulose fibers have a number-average fiber diameter of 2 nm to 1000 nm and an alkali-soluble polysaccharide content of 20% by mass or less.
The cellulose fiber dry body has an angle of repose of 40° to 60°, a difference angle of 10° or less, a loose bulk density of 0.01 g/ ^cm³ to 0.40 g/ ^cm³ , a dense bulk density of 0.1 g/ ^cm³ to 0.55 g/ ^cm³ , and a degree of compressibility of 20% to 40%. The cellulose fiber dried body according to claim 1 , wherein the average fiber length (L) / fiber diameter (D) ratio of the cellulose fibers is 30 to 5000. The cellulose fiber dried body according to claim 1 or 2 , wherein the cellulose fiber has 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. The cellulose fiber dried body according to any one of claims 1 to 3 , wherein the degree of crystallinity of the cellulose fibers is 60% or more. A dried cellulose fiber according to any one of claims 1 to 4 , wherein the moisture content is 30% by mass or less. The cellulose fiber dry product according to any one of claims 1 to 5 , wherein the dispersant is a compound having an HLB value of 0.1 or more and less than 8.0, a melting point of 80°C or less, and a number average molecular weight of 1,000 to 50,000. A method for producing a dried cellulose fiber according to any one of claims 1 to 6 ,
A slurry preparation step of preparing a slurry containing cellulose fibers and an aqueous medium, and a drying step of drying the slurry under conditions of a drying rate of 10%/min to 10000%/min to form a dried cellulose fiber body.
Methods that include... The method according to claim 7 , wherein the drying step is carried out as a continuous process with a drying temperature of 20°C to 200°C and a residence time of 0.01 minutes to 10 minutes. A method for producing a resin composite containing cellulose fibers and resin,
The method comprises mixing a cellulose fiber dry product according to any one of claims 1 to 6 with a resin,
A method wherein the tensile elongation at break of the resin composite is 8% or more. The method according to claim 9 , wherein the resin is a thermoplastic resin. The method according to claim 10 , wherein the thermoplastic resin is a polyamide resin.