JP7488096B2 - Dried cellulose fiber body, its manufacturing method, and manufacturing method of resin composite - Google Patents

Description

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

Resin materials are light and have excellent processing properties, and are therefore widely used in many areas, such as automobile parts, electrical and electronic parts, office equipment housings, and precision parts. However, resin alone often has insufficient mechanical properties and dimensional stability, so composites of resin and various fillers are generally used. In recent years, the use of nanofibers such as cellulose nanofibers (CNF) as such fillers has been considered. Nanofibers such as CNF tend to aggregate easily in a dry state, so they are manufactured as a dispersion liquid that allows stable dispersion. For example, when applying cellulose nanofibers to various applications, the above dispersion liquid may be dried once and then dispersed in a dispersion medium, or may be redispersed in a matrix resin while still in the dried form. However, in cellulose nanofibers, aggregation due to hydrogen bonds between cellulose molecules is extremely strong, so various methods have been proposed to suppress aggregation of cellulose nanofibers during the drying process.

For example, Patent Document 1 describes a powdered nanofiber that is characterized by being made by blending (A) powdered nanofiber with (B) dispersant at 1 to 40% by weight, calculated as solid content, and having a bulk density of 90 to 200 g/L. Patent Document 2 describes a method for producing dried microfibers with a moisture 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 a dry cellulose nanofiber solid, which includes drying a mixture of cellulose nanofibers and a solvent using a vacuum drying device.

JP 2017-210596 A JP 2012-224960 A International Publication No. 2019/189318

All of the techniques described in Patent Documents 1 to 3 aim to reduce the aggregation of cellulose nanofibers during drying, thereby allowing the cellulose nanofibers to be well redispersed in a dispersion medium or matrix resin after drying. However, even with these techniques, the redispersibility of cellulose nanofibers once dried is insufficient, and in particular, no technique has been established that allows the cellulose nanofibers to be well dispersed in a resin even when mixed with the resin in a dry state. Therefore, with conventional techniques, the effect of improving the physical properties of the resin by the cellulose nanofibers cannot be expressed at a satisfactory level, and in addition, there are agglomerates that do not pass through the screen mesh during mass production, which means that the screen mesh must be replaced very frequently, making mass production difficult.

One aspect of the present invention aims to solve the above problems and provide a dried cellulose fiber body that is unlikely to form aggregates that cause defects such as black spots when mixed with resin, has excellent productivity by reducing the frequency of screen mesh replacement during molding processing, and can give a resin composite that has high toughness and excellent appearance, as well as a resin composite containing the dried cellulose fiber body and a resin.

The present invention includes the following aspects.
[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/cm ³ to 0.40 g/cm ³ , a packed bulk density of 0.1 g/cm ³ to 0.55 g/cm ³ , and a compression degree of 20% to 40%, and having a content of particle components having a particle size of 710 μm or less of 50% by mass to 90% by mass.
[2] The dried cellulose fiber according to the above aspect 1, wherein the content of particulate components having a particle size of more than 710 μm and not more than 1000 μm is 10% by mass to 30% by mass.
[3] The dried cellulose fiber according to the above aspect 1 or 2, wherein the content of particle components having a particle size of more than 1000 μm is 1% by mass to 10% by mass.
[4] The dried cellulose fiber material according to any one of aspects 1 to 3, wherein the number average fiber diameter of the cellulose fibers is 2 nm to 1000 nm.
[5] The dried cellulose fiber according to any one of the above aspects 1 to 4, wherein the cellulose fiber has an average fiber length (L)/fiber diameter (D) ratio of 30 to 5,000.
[6] The dried cellulose fiber according to any one of aspects 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 dried cellulose fiber material according to any one of aspects 1 to 6, wherein the cellulose fiber has a crystallinity of 60% or more.
[8] The dried cellulose fiber material according to any one of aspects 1 to 7, wherein the cellulose fiber has an alkali-soluble polysaccharide content of 20 mass% or less.
[9] The dried cellulose fiber material according to any one of the above aspects 1 to 8, wherein the cellulose fiber is chemically modified.
[10] The dried cellulose fiber material according to the above-mentioned aspect 9, wherein the chemical modification is esterification.
[11] The dried cellulose fiber material according to the above aspect 10, wherein the esterification is acetylation.
[12] The dried cellulose fiber according to any one of aspects 9 to 11, wherein the cellulose fiber has an average degree of substitution (DS) of 0.1 to 1.2.
[13] The dried cellulose fiber according to any one of aspects 1 to 12, having a moisture content of 30% by mass or less.
[14] Further comprising a dispersant,
The dried cellulose fiber material according to any one of the above aspects 1 to 13, 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.
[15] A method for producing a dried cellulose fiber material according to any one of aspects 1 to 14, comprising the steps of:
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 10,000%/min to form a dried cellulose fiber body.
A method comprising:
[16] The method according to the above-mentioned aspect 15, wherein the drying step is carried out in a continuous process with a residence time of 0.01 minutes to 10 minutes at a drying temperature of 20°C to 200°C.
[17] A method for producing a resin composite containing cellulose fibers and a resin, comprising:
The present invention includes mixing the dried cellulose fiber material according to any one of Aspects 1 to 16 with a resin,
The resin composite has a tensile elongation at break of 8% or more.
[18] The method according to claim 17, wherein the resin is a thermoplastic resin.
[19] The method according to claim 18, wherein the thermoplastic resin is a polyamide resin.

According to one aspect of the present invention, a dried cellulose fiber body that is unlikely to form aggregates that cause defects such as black spots when mixed with a resin, has excellent productivity by reducing the frequency of screen mesh replacement during molding processing, and can give a resin composite that has high toughness and excellent appearance, and a resin composite containing the dried cellulose fiber body and a resin can be provided.

FIG. 10 is an explanatory diagram of a method for calculating the IR index 1730 and the IR index 1030. FIG. 2 is an explanatory diagram of a method for measuring the thermal decomposition onset temperature (T _D ) and the 1% weight loss temperature (T _1% ).

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

<Dried cellulose fiber>
One aspect of the present invention provides a dried cellulose fiber material, which may be particulate. The dried cellulose fiber material according to one aspect has a particle size, angle of repose, angle of collapse, difference angle, loose bulk density, packed bulk density, and degree of compression controlled within specific ranges. Such dried cellulose fiber material is unlikely to form cellulose aggregates that cause defects such as black spots when dispersed in a resin, because the particle size, cellulose molecular aggregation state, and interparticle interaction are appropriately controlled. Therefore, by using the dried cellulose fiber material according to one aspect of the present invention, a resin composite can be formed that has high toughness, has few defects such as cellulose-derived black spots, and exhibits a good appearance.

In one embodiment, the angle of repose of the dried cellulose fiber body is 40° to 60°, preferably 42° or more, or 44° or more, or 46° or more, and preferably 58° or less, or 56° or less, or 54° or less. If the size of the dried cellulose fiber body is too large, it is difficult to disperse it in the resin, but if it is too small, aggregation between particles becomes significant and dispersibility in the resin worsens. The dried cellulose fiber body having an angle of repose in the above range can disperse the cellulose fibers uniformly in the resin because the particle size is in a moderate range. Note that the dispersion size in this case is not necessarily extremely fine, but the physical properties (especially toughness) of the resin composite are extremely good due to the small amount of aggregates generated.

The collapse angle of the dried cellulose fiber body is controlled to a range that is useful for controlling the angle of repose and the difference angle within the ranges disclosed herein, 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 dried cellulose fiber body (i.e., the difference between the angle of repose and the angle of collapse) is 10° or less, and may be preferably 9° or less, or 8° or less, or 7° or less. A dried cellulose fiber body having a difference angle in the above range has excellent handleability due to a relatively large interaction between particles (frictional force, etc.). From the viewpoint of ease of manufacturing the dried cellulose fiber body, the difference angle may be, for example, 1° or more, or 2° or more, or 3° or more.

The angle of repose and the angle of collapse are values measured using the method 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 loose bulk density of the dried cellulose fiber body is 0.01 g/cm 3 or more, preferably 0.05 g/cm 3 or more, or 0.08 g/cm 3 or more, or 0.1 g/cm ³ or more, from the viewpoint of avoiding inconveniences such as particles scattering due to the dried cellulose fiber body being too light, or the dried cellulose fiber body floating on the upper part of the resin phase when mixed with a fluidized resin, resulting in poor mixing. The loose bulk density may be 0.40 g/cm ³ or less, preferably 0.38 g/cm ³ or less, or 0.36 g ^/ cm ³ or less, or 0.35 g/cm ³ or less, from the viewpoints that the cellulose fibers can be well dispersed in the resin, and that the dried cellulose fiber body is not too heavy and poor ^mixing between the dried cellulose fiber body and ^the resin can be avoided.

The packed bulk density of the dry cellulose fiber body is controlled within a range that is useful for controlling the loose bulk density and compressibility within the ranges of the present disclosure, and in one embodiment, may be 0.1 g/cm ³ to 0.55 g/cm ³ , or 0.12 g/cm ³ to 0.52 g/cm ³ , or 0.13 g/cm ³ to 0.2 g/cm ³ .

In one embodiment, the compression degree of the dried cellulose fiber body is 20% to 40%. The compression degree indicates the degree of bulk loss. In order to prevent the fluidity of the dried cellulose fiber body from being too high and to suppress natural flow, the compression degree is 20% or more, and preferably 23% or more, or 25% or more, or 27% or more. In order to ensure good fluidity of the dried cellulose fiber body, the compression degree is 40% or less, and preferably 39% or less, or 38% or less, or 37% or less.

The loose bulk density and packed bulk density are values measured using the method described in the [Examples] section of this disclosure. The compression degree is calculated as follows: compression degree = (packed bulk density - loose bulk density) / packed bulk density.

In one embodiment, the content of particle components having a particle diameter of 710 μm or less in the dried cellulose fiber body is 50 to 90% by mass, and may be preferably 55 to 85% by mass, or 60 to 80% by mass, or 63 to 77% by mass. The content of particles having a particle diameter of more than 710 μm and not more than 1000 μm may be preferably 10 to 30% by mass, or 12 to 25% by mass. The content of particles having a particle diameter of more than 1000 μm may be preferably 1 to 22% by mass, or 5 to 10% by mass. In the dried cellulose fiber body, small particles having a particle diameter of 710 μm or less are the main component, so that the dried cellulose fiber body can be easily dispersed in the resin, and clogging of the screen mesh can be suppressed while improving toughness. In addition, by appropriately containing particles having a particle diameter larger than 710 μm, rigidity can be expressed, and therefore a resin composite having excellent balance of physical properties can be obtained. The particle size distribution of the dried cellulose fiber body is a value measured by the method described in the section [Examples] of this disclosure.

In one embodiment, the average particle size of the dried cellulose fiber body is preferably 50 μm or more, or 100 μm or more, or 200 μm or more, or 500 μm or more, and is 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 a laser diffraction/scattering method.

In one embodiment, the moisture content of the dried cellulose fiber body may be 30% by mass or less, or 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 production of the dried cellulose fiber body, 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 moisture meter.

As the raw material for the dried cellulose fiber body, natural cellulose and regenerated cellulose can be used. As the natural cellulose, wood pulp obtained from wood species (broadleaf or coniferous trees), 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) can be used. As the regenerated cellulose, regenerated cellulose fibers (viscose, cupra, tencel, etc.), cellulose derivative fibers, and ultra-fine threads of regenerated cellulose or cellulose derivatives obtained by the electrospinning method can be used.

In one embodiment, the cellulose fibers are cellulose nanofibers. Cellulose nanofibers refer to fine cellulose fibers that are obtained by treating pulp or the like with hot water of 100°C or higher to hydrolyze and weaken the hemicellulose, and then defibrating the fibers by a pulverizing method using a high-pressure homogenizer, microfluidizer, ball mill, disk mill, mixer (e.g., homomixer), or the like. In one embodiment, the cellulose nanofibers have a number-average fiber diameter of 1 nm or more and 1000 nm or less. The cellulose fibers may be chemically modified as described below.

The slurry can be prepared by dispersing cellulose fibers (e.g., cellulose nanofibers obtained through the above-mentioned defibration) in a liquid medium. The dispersion may be performed using a high-pressure homogenizer, a microfluidizer, a ball mill, a disk mill, a mixer (e.g., a homomixer), or the like. For example, the product of the above-mentioned defibration may be obtained as the product of the slurry preparation process of the present disclosure. In addition to water, the liquid medium in the slurry may further contain other liquid media (e.g., organic solvents) in any combination of one or more types. As the organic solvent, a commonly used water-miscible organic solvent, for example: alcohols having a boiling point 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.), etc. can be used. In a typical embodiment, the liquid medium in the slurry is substantially only water. In addition to the cellulose fibers and the liquid medium, the slurry may contain additional components (dispersants, binders, antioxidants, preservatives, thickeners, etc.) described below.

Cellulose fiber raw materials contain alkali-soluble and sulfuric acid-insoluble components (such as lignin), so they may be subjected to a refining process such as delignification by cooking and a bleaching process to reduce the alkali-soluble and sulfuric acid-insoluble components. On the other hand, refining processes such as delignification by cooking and a bleaching process cut the molecular chains of cellulose, changing the weight-average molecular weight and number-average molecular weight, so it is desirable that the refining and bleaching processes of cellulose fiber raw materials are controlled so that the weight-average molecular weight of cellulose and the ratio of the weight-average molecular weight to the number-average molecular weight do not deviate from the appropriate range.

In addition, refining processes such as delignification by cooking and bleaching processes reduce the molecular weight of cellulose molecules, and there is concern that these processes will result in low molecular weight cellulose and alter the cellulose fiber raw material, increasing the proportion of alkali-soluble matter present. Since alkali-soluble matter has poor heat resistance, it is desirable that the refining and bleaching processes of cellulose fiber raw materials be controlled so that the amount of alkali-soluble matter contained in the cellulose fiber raw material is within a certain range or less.

In one aspect, 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. The number average fiber diameter of the cellulose fibers is more preferably 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more, and more preferably 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 of the cellulose fibers is preferably 50 or more, or 80 or more, or 100 or more, or 120 or more, or 150 or more, from the viewpoint of effectively improving the mechanical properties of the resin composite containing the cellulose fibers with a small amount of cellulose fibers. The upper limit is not particularly limited, but is preferably 5000 or less from the viewpoint of handleability.

In the present 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 processing conditions: rotation speed 15,000 rpm x 5 minutes, diluting the aqueous dispersion with pure water to 0.1 to 0.5 mass%, casting it on mica, and air-drying it to obtain a measurement sample, and measuring it with 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 where the magnification is adjusted so that at least 100 cellulose fibers are observed, and the ratio (L/D) is calculated. The number average value of the length (L), the number average value of the diameter (D), and the number average value of the ratio (L/D) are calculated for the cellulose fibers.

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

Alternatively, the length, diameter, and L/D ratio of the cellulose fibers in the resin composite can be confirmed by dissolving the resin components in the resin composite in an organic or inorganic solvent capable of dissolving the resin components of the resin composite, separating the cellulose fibers, thoroughly washing the fibers with the solvent, and then replacing the solvent with pure water to prepare an aqueous dispersion. The cellulose fiber concentration is diluted with pure water to 0.1 to 0.5% by mass, cast on mica, and air-dried to obtain a measurement sample, which is then measured using the above-mentioned measurement method. At this time, the measurement is performed on 100 or more randomly selected cellulose fibers.

The crystallinity of the cellulose fibers is preferably 55% or more. When the crystallinity is in this range, the mechanical properties (strength, dimensional stability) of the cellulose fibers themselves are high, so that when the cellulose fibers are dispersed in a resin, the strength and dimensional stability of the resin composite tend to be high. A more preferable lower limit of 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, and the higher the better, but from a production standpoint, a preferable upper limit is 99%.

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

When the cellulose is cellulose I type crystal (derived from natural cellulose), the degree of crystallinity is determined by the Segal method from a diffraction pattern (2θ/deg. is 10 to 30) obtained by measuring a sample by wide-angle X-ray diffraction, according to the following formula:
Crystallinity (%)=([diffraction intensity attributable to the (200) plane at 2θ/deg.=22.5]−[diffraction intensity attributable to amorphous at 2θ/deg.=18])/[diffraction intensity attributable to the (200) plane at 2θ/deg.=22.5]×100

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

Known crystalline forms of cellulose include types I, II, III, and IV, of which types I and II are particularly widely used, and types III and IV have been obtained on a laboratory scale but are not widely used on an industrial scale. The cellulose fibers disclosed herein have relatively high structural mobility, and by dispersing the cellulose fibers in a resin, a resin composite is obtained that has a lower linear expansion coefficient and is superior in strength and elongation during tensile and bending deformation. Therefore, cellulose fibers containing cellulose type I crystals or cellulose type II crystals are preferred, and cellulose fibers containing cellulose type I crystals and having a crystallinity of 55% or more are more preferred.

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

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

The degree of polymerization of cellulose fibers refers to the average degree of polymerization measured according to the reduced specific viscosity method using a copper-ethylenediamine solution as described in the Verification Test (3) of the "Japanese Pharmacopoeia Commentary, 15th Edition (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 (Mw/Mn) of the weight average molecular weight to the number average molecular weight (Mn) is 6 or less, preferably 5.4 or less. The larger the weight average molecular weight, the fewer the number of terminal groups of the cellulose molecule. In addition, since the ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight represents the width of the molecular weight distribution, the smaller the Mw/Mn, the fewer the number of terminals of the cellulose molecule. Since the terminals of the cellulose molecules are the starting points of thermal decomposition, when the cellulose molecules of the cellulose fibers not only have a large weight average molecular weight but also have a narrow molecular weight distribution, a particularly high heat resistant cellulose fiber and a resin composite containing the cellulose fiber and the resin can be obtained. The weight average molecular weight (Mw) of the cellulose fiber may be, for example, 600,000 or less, or 500,000 or less, from the viewpoint of the ease of availability of the cellulose fiber raw material. From the viewpoint of ease of production of cellulose fibers, the ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight (Mn) may be, for example, 1.5 or more, or 2 or more. Mw can be controlled to the above range by selecting a cellulose fiber raw material having an Mw appropriate for the purpose, performing physical and/or chemical treatment on the cellulose fiber raw material appropriately in a moderate range, etc. Mw/Mn can also be controlled to the above range by selecting a cellulose fiber raw material having an Mw/Mn appropriate for the purpose, performing physical and/or chemical treatment on the cellulose fiber raw material appropriately in a moderate range, etc. In both the control of Mw and the control of Mw/Mn, examples of the physical treatment include dry or wet grinding using a microfluidizer, ball mill, disk mill, etc., physical treatment that applies mechanical forces such as impact, shear, shear, and friction using a crusher, homomixer, high-pressure homogenizer, ultrasonic device, etc., and examples of the chemical treatment include digestion, bleaching, acid treatment, regenerated cellulose, etc.

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

Methods for controlling the degree of polymerization (i.e., average degree of polymerization) or molecular weight of cellulose fibers include hydrolysis. Hydrolysis promotes depolymerization of the amorphous cellulose inside the cellulose fibers, decreasing the average degree of polymerization. At the same time, hydrolysis removes impurities such as hemicellulose and lignin in addition to the amorphous cellulose described above, making the inside of the fibers more porous.

The hydrolysis method is not particularly limited, and examples thereof include acid hydrolysis, alkali hydrolysis, hydrothermal decomposition, steam explosion, and microwave decomposition. These methods may be used alone or in combination of two or more. In the acid hydrolysis method, for example, α-cellulose obtained as pulp from a fibrous plant is used as the cellulose fiber raw material, and this is dispersed in an aqueous medium, and an appropriate amount of protonic acid, carboxylic acid, Lewis acid, heteropolyacid, etc. is added and heated while stirring, so that the average degree of polymerization can be easily controlled. The reaction conditions such as temperature, pressure, and time at this time vary depending on the cellulose type, cellulose concentration, acid type, acid concentration, etc., but are appropriately adjusted so that the desired average degree of polymerization is achieved. For example, a condition is that a mineral acid aqueous solution of 2% by mass or less is used, and the cellulose fiber is treated at 100°C or higher under pressure for 10 minutes or more. Under these conditions, the catalyst component such as acid penetrates into the inside of the cellulose fiber, promoting hydrolysis, reducing the amount of catalyst component used, and making subsequent purification easier. In addition, the dispersion of the cellulose fiber raw material during hydrolysis may contain a small amount of an organic solvent in addition to water, as long as the effects of the present invention are not impaired.

Alkali-soluble polysaccharides that cellulose fibers may contain include hemicellulose, 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). Alkali-soluble polysaccharides are polysaccharides that contain hydroxyl groups and have poor heat resistance, and can cause problems such as decomposition when exposed to heat, yellowing during thermal aging, and a decrease in the strength of cellulose fibers. Therefore, it is preferable that the content of alkali-soluble polysaccharides in cellulose fibers is low.

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. From the viewpoint of ease of production 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.

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

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 associated discoloration. From the viewpoint of ease of production of the cellulose fibers, the above content may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more.

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

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

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

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

The 250° C. weight loss rate (T _{250° C.} ) of a cellulose fiber is the weight loss rate when the cellulose fiber is held at 250° C. under a nitrogen flow for 2 hours in a TG analysis.

(Chemical Modification)
The cellulose fibers may be chemically modified cellulose fibers, for example, the cellulose fibers may be chemically modified in advance at the raw pulp or linter stage, during or after the defibration process, or during or after the slurry preparation process, or during or after the drying (granulation) process.

As a modification agent for cellulose fibers, a compound that reacts with the hydroxyl groups of cellulose can be used, and examples of such agents include esterifying agents, etherifying agents, and silylating agents. In a preferred embodiment, the chemical modification is acylation using an esterifying agent. As an esterifying agent, acid halides, acid anhydrides, vinyl carboxylates, and carboxylic acids are preferred.

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 represents Cl, Br, or I.)
Specific examples of acid halides include, but are not limited to, acetyl chloride, acetyl bromide, acetyl iodide, propionyl chloride, propionyl bromide, propionyl iodide, butyryl chloride, butyryl bromide, butyryl iodide, benzoyl chloride, benzoyl bromide, and benzoyl iodide. Among them, acid chlorides can be preferably used in terms of reactivity and handling. In addition, in the reaction of acid halides, one or more alkaline compounds may be added to act as a catalyst and neutralize the by-product acidic substances. Specific examples of alkaline compounds include, but are not limited to, tertiary amine compounds such as triethylamine and trimethylamine; and nitrogen-containing aromatic compounds such as pyridine and dimethylaminopyridine.

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

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

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

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

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

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

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

The carboxylic acid may be 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, cyclohexane carboxylic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, pivalic acid, methacrylic acid, crotonic acid, pivalic acid, octylic acid, benzoic acid, and cinnamic acid.

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

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

When the cellulose fibers in the dried cellulose fiber body are chemically modified (for example, by hydrophobization such as acylation), the dispersibility of the dried body in the resin tends to be good, but the dried cellulose fiber body of the present disclosure can exhibit good dispersibility in the resin even if it is unsubstituted or has a low degree of substitution. When the cellulose fibers in the dried cellulose fiber body are esterified cellulose fibers, the acyl substitution degree (DS) is preferably 0.1 or more, or 0.2 or more, or 0.25 or more, or 0.3 or more, or 0.5 or more, in terms of being able to obtain esterified cellulose fibers and resin composites containing the same with a high thermal decomposition onset temperature, and is preferably 1.2 or less, or 1.0 or less, or 0.8 or less, or 0.7 or less, or 0.6 or less, or 0.5 or less, in terms of being able to obtain esterified cellulose fibers and resin composites containing the same with a high thermal decomposition onset temperature due to the remaining unmodified cellulose skeleton in the esterified cellulose fibers.

When the modifying group of the chemically modified cellulose fiber is an acyl group, the degree of acyl substitution (DS) can be calculated from the reflection infrared absorption spectrum of the esterified cellulose fiber based on the peak intensity ratio between the peak derived from the acyl group and the peak derived from the cellulose skeleton. The peak of the absorption band of C=O based on the acyl group appears at 1730 cm ^-1 , and the peak of the absorption band of C-O based on the cellulose skeleton appears at 1030 cm ^-1 (see FIG. 1). The DS of the esterified cellulose fiber is calculated by preparing a correlation graph between the DS obtained from the solid-state NMR measurement of the esterified cellulose fiber described below and the modification ratio (IR index 1030) defined as the ratio of the peak intensity of the absorption band of C=O based on the acyl group to the peak intensity of the absorption band of C-O of the cellulose skeleton, and calculating the calibration curve substitution degree DS=4.13×IR index (1030) from the correlation graph.
It can be found by using

The DS of the esterified cellulose fiber can be calculated by solid-state NMR by performing ^13C solid-state NMR measurement on the frozen and pulverized esterified cellulose fiber, and calculating the DS from the total intensity (Inp) of the signals assigned to carbons C1 to C6 derived from the pyranose ring of cellulose appearing in the range from 50 ppm to 110 ppm relative to the intensity (Inf) of a signal assigned to one carbon atom derived from the modifying group, using the following formula:
DS = (Inf) x 6 / (Inp)
For example, when the modifying group is an acetyl group, the signal at 23 ppm assigned to _--CH.sub.3 may be used.
The conditions for the ¹³ C solid state NMR measurement are, for example, as follows:
Equipment: Bruker Biospin Avance 500WB
Frequency: 125.77MHz
Measurement method: DD/MAS method Waiting time: 75 sec
NMR sample tube: 4 mm diameter
Total number of times: 640 times (approximately 14 hours)
MAS: 14,500Hz
Chemical shift reference: glycine (external reference: 176.03 ppm)

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

The smaller the coefficient of variation (CV) of the DS heterogeneity ratio of the chemically modified cellulose fiber, the smaller the variation in various physical properties of the resin composite, and therefore the more preferable. The coefficient of variation is preferably 50% or less, or 40% or less, or 30% or less, or 20% or less. The coefficient of variation can be further reduced, for example, by a method in which the cellulose fiber raw material is defibrated and then chemically modified to obtain chemically modified cellulose fiber (i.e., a sequential method), whereas it can be increased by a method in which the defibration and chemical modification of the cellulose fiber raw material are performed simultaneously (i.e., a simultaneous method). Although the mechanism of this action is not clear, in the simultaneous method, chemical modification is more likely to proceed in the thin fibers generated in the early stages of defibration, and it is believed that defibration proceeds further when the hydrogen bonds between cellulose microfibrils are reduced by chemical modification, 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 by taking 100 g of an aqueous dispersion of chemically modified cellulose fiber (solid content of 10 mass% or more), freeze-pulverizing 10 g each to prepare measurement samples, calculating the DS heterogeneity ratio from the DSt and DSs of the 10 samples, and then using the standard deviation (σ) and arithmetic mean (μ) of the DS heterogeneity ratio among the obtained 10 samples, using the following formula.
DS heterogeneity ratio = DSs / DSt
Coefficient of variation (%) = standard deviation σ/arithmetic mean μ × 100

The DSs is calculated as follows. That is, the esterified cellulose fiber powdered by freeze-pulverization is placed on a dish-shaped sample stage with a diameter of 2.5 mm, the surface is pressed down to make it flat, and measurement is performed by X-ray photoelectron spectroscopy (XPS). The XPS spectrum reflects the constituent elements and chemical bond state of only the surface layer of the sample (typically about a few nm). Peak separation is performed on the obtained C1s spectrum, and DSs can be calculated by the following formula based on the integrated intensity (Ixf) of the peak attributable to one carbon atom derived from the modifying group relative to the integrated intensity (Ixp) of the peak (289 eV, C-C bond) attributable to carbons C2-C6 derived from the pyranose ring of cellulose.
DSs = (Ixf) x 5/(Ixp)
For example, when the modifying group is an acetyl group, the C1s spectrum is subjected to peak separation at 285 eV, 286 eV, 288 eV, and 289 eV, and then the peak at 289 eV is used as Ixp, and the peak (286 eV) derived from the O—C═O bond of the acetyl group is used as Ixf.
The conditions for the XPS measurement are, for example, as follows:
Equipment used: ULVAC-Phi VersaProbe II
Excitation source: mono. AlKα 15 kV x 3.33 mA
Analysis size: Approximately 200 μm φ
Photoelectron take-off angle: 45°
Capture area Narrow scan: C 1s, O 1s
Pass Energy: 23.5 eV

[Additional Ingredients]
In addition to the cellulose fibers, the dry cellulose fiber material may further contain additional components such as a dispersant, a binder, an antioxidant, a preservative, and a thickener.

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

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

From the viewpoint of suppressing the aggregation of cellulose fibers, the dispersant is preferably a water-soluble polymer. In this disclosure, "water-soluble" means that 0.1 g or more is dissolved in 100 g of water at 23°C. Furthermore, it is more preferable that the dispersant has a hydrophilic segment and a hydrophobic segment (i.e., is an amphipathic molecule) from the viewpoint of dispersing cellulose fibers more uniformly in the resin. Examples of amphipathic molecules include those having a carbon atom as a basic skeleton and a functional group composed of an element selected from carbon, hydrogen, oxygen, nitrogen, chlorine, sulfur, and phosphorus. As long as the molecule has the above structure, those in which an inorganic compound and the above functional group are chemically bonded are also preferable. The hydrophilic segment has good affinity with the surface of the cellulose fiber, and the hydrophobic segment has the characteristic of suppressing the aggregation of cellulose fibers through the hydrophilic segment and being easily compatible with the resin. Therefore, it is preferable that the hydrophilic segment and the hydrophobic segment are present in 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 indicating the balance between the hydrophobicity and hydrophilicity of a surfactant, and takes values from 1 to 20, with a smaller value indicating stronger hydrophobicity and a larger value indicating stronger hydrophilicity. In the present disclosure, the HLB value is a value calculated by the following formula according to the Griffin method. In the following formula, the "sum of formula weights of hydrophilic groups/molecular weight" is the mass % of the hydrophilic groups.
Formula 1) Griffin method: HLB value = 20 x (sum of formula weights of hydrophilic groups / molecular weight)

From the viewpoint of ease of solubility in water, 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 uniform dispersion of cellulose fibers in the resin, the upper limit of the HLB value is preferably less than 8, more preferably 7.5, and most preferably 7.

In a typical embodiment, the hydrophilic segment is a portion that exhibits good affinity with cellulose fibers by containing a hydrophilic structure (e.g., one or more hydrophilic groups selected from hydroxyl groups, carboxy 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 containing quaternary ammonium salt structures, polyvinyl alcohol segments, polyvinylpyrrolidone segments, polyacrylic acid segments, carboxyvinyl polymer segments, cationized guar gum segments, hydroxyethyl cellulose segments, methyl cellulose segments, carboxymethyl cellulose segments, and polyurethane soft segments (specifically diol segments). In a preferred embodiment, the hydrophilic segment contains an oxyethylene unit.

Examples of the hydrophobic segment include a segment having an alkylene oxide unit having 3 or more carbon atoms (for example, a PPG block) and a segment containing the following polymer structure:
Examples of the polycondensates include acrylic polymers, styrene resins, vinyl chloride resins, vinylidene chloride resins, polyolefin resins, polyhexamethylene adipamide (6,6 nylon), polyhexamethylene azelamide (6,9 nylon), polyhexamethylene sebacamide (6,10 nylon), polyhexamethylene dodecanoamide (6,12 nylon), polybis(4-aminocyclohexyl)methanedodecane, and other polycondensates of organic dicarboxylic acids having 4 to 12 carbon atoms and organic diamines having 2 to 13 carbon atoms, and polycondensates of ω-amino acids (for example, ω-aminoundecanoic acid) (for example, polyundecaneamide (1 poly(aminocaprolactam) (nylon 1), etc.), amino acid lactams including ring-opening polymerization products of lactams such as polycapramide (nylon 6) which is a ring-opening polymerization product of ε-aminocaprolactam, and polylauriclactam (nylon 12) which is a ring-opening polymerization product of ε-aminolaurolactam, polymers composed of diamines and dicarboxylic acids, polyacetal resins, polycarbonate resins, polyester resins, polyphenylene sulfide resins, polysulfone resins, polyether ketone resins, polyimide resins, fluorine-based 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 in the molecule.

The dispersant may have a graft copolymer structure and/or a block copolymer structure. These structures may be one type alone or two or more types. When two or more types are used, the dispersant may be a polymer alloy. In addition, the dispersant may be a partially modified or terminally modified (acid modified) copolymer.

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 block copolymers, ABA block copolymers, BAB block copolymers, ABAB block copolymers, ABABA block copolymers, BABAB block copolymers, tri-branched copolymers containing A and B, tetra-branched copolymers containing A and B, star copolymers containing A and B, monocyclic copolymers containing A and B, polycyclic copolymers containing A and B, cage copolymers containing A and B, etc.

The structure of the dispersant is preferably an AB block copolymer, an ABA triblock copolymer, a three-branched copolymer containing A and B, or a four-branched copolymer containing A and B, and more preferably an ABA triblock copolymer, a three-branched structure (i.e., a three-branched copolymer containing A and B), or a four-branched structure (i.e., a four-branched copolymer containing A and B). In order to ensure good affinity with cellulose fibers, it is desirable for the dispersant to have the above structure.

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

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

In a typical embodiment, the dispersant has a cloud point. When the temperature of an aqueous solution of a nonionic surfactant having a polyether chain such as a polyoxyethylene chain as a hydrophilic site is increased, the transparent or translucent aqueous 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 drops sharply at a certain temperature, and the surfactants that were dissolved up until that point aggregate and become cloudy, separating from the water. This is thought to be because the nonionic surfactant loses its hydration power at high temperatures (the hydrogen bonds between the polyether chain and water are broken, and the solubility in water drops sharply). The longer the polyether chain, the lower the cloud point tends to be. Since the dispersant dissolves in any proportion in water at temperatures below the cloud point, the cloud point is a measure of the hydrophilicity of the dispersant.

The cloud point of a dispersant can be measured by the following method. Using a tuning fork type vibration viscometer (e.g. SV-10A manufactured by A&D Co., Ltd.), the aqueous solution of the dispersant is adjusted to 0.5 mass%, 1.0 mass%, and 5 mass%, and measurements are taken at temperatures ranging from 0 to 100°C. At this time, the point showing the inflection point (the point where the viscosity increases or the aqueous solution becomes cloudy) at each concentration is taken as the cloud point.

From the viewpoint of ease of handling, the lower limit of the cloud point of the dispersant is preferably 10°C, more preferably 20°C, and most preferably 30°C. 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. To ensure good affinity with cellulose fibers, it is desirable for the cloud point of the dispersant to be within the above-mentioned range.

Dispersants with a solubility parameter (SP value) of 7.25 or more are preferred. When the dispersant has an SP value in this range, the dispersibility of the cellulose fibers in the resin is improved.

According to a document by Foders (R.F. Foders: Polymer Engineering & Science, vol. 12(10), p. 2359-2370 (1974)), the SP value depends on both the cohesive energy density and the molar molecular weight of the substance, and these are also thought to depend on the type and number of substituents of the substance. According to a document by Ueda et al. (Research on Paints, No. 152, October 2010), the SP values (Cal/ ^Cm3 ) ^1/2 for existing major solvents shown in the examples below are published.

The SP value of a dispersant can be experimentally determined from the boundary between soluble and insoluble when the dispersant is dissolved in various solvents with known SP values. For example, when 1 mL of dispersant is dissolved in various solvents (10 mL) with different SP values at room temperature for 1 hour under stirring with a stirrer, it can be determined whether the entire amount dissolves. For example, if a dispersant is soluble in diethyl ether, the SP value of that dispersant will be 7.25 or more.

Dispersants (especially amphipathic molecules) preferably have a boiling point higher than that of water, and more preferably have a boiling point higher than the melting point of the resin from the viewpoint of uniformly dispersing the cellulose fibers in the resin during melt kneading. A boiling point higher than that of water refers to a boiling point higher than the boiling point of water at each pressure on the vapor pressure curve (for example, 100°C at 1 atmosphere).

By selecting a dispersant that has a boiling point higher than that of water, for example, in the process of drying a slurry containing water as a liquid medium in the presence of the dispersant to obtain a dried cellulose fiber body, the water and the dispersant are replaced during the evaporation of the water, and the dispersant is present on the surface of the cellulose fibers, thereby achieving the effect of significantly suppressing the aggregation of the cellulose fibers.

The method of adding the dispersant is not limited.
A method for producing a dried cellulose fiber body by mixing a dispersant with cellulose fibers after a drying step,
A method for producing a dried cellulose fiber body, comprising adding a dispersant to a slurry in which cellulose fibers are dispersed in a liquid medium, and then drying the slurry to obtain a dried cellulose fiber body;
In the production of a resin composite, a resin, a dried cellulose fiber or a redispersion obtained by dispersing the dried cellulose fiber in a liquid medium, and a dispersant are mixed in advance, melt-kneaded, and then molded;
In the production of a resin composite, a dispersant is added to the resin in advance, and if necessary, pre-mixing is performed. Then, a dried cellulose fiber or a re-dispersion obtained by dispersing the dried cellulose fiber in a liquid medium is added, and the mixture is melt-kneaded and molded.
etc.

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

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 a resin complex, the amount of dispersant can be easily confirmed by a method common to those skilled in the art. The confirmation method is not limited, but the following method can be exemplified. Using broken pieces of a resin complex, the broken pieces are dissolved in a solvent that dissolves resin, and soluble portion 1 (resin and dispersant) and insoluble portion 1 (cellulose fiber and dispersant) are separated. Soluble portion 1 is reprecipitated in a solvent that does not dissolve resin but dissolves dispersant, and separated into insoluble portion 2 (resin) and soluble portion 2 (dispersant). Insoluble portion 1 is also dissolved in a dispersant-soluble solvent, and separated into soluble portion 3 (dispersant) and insoluble portion 3 (cellulose fiber). The amount of dispersant can be quantified by concentrating soluble portions 2 and 3 (drying, air drying, drying under reduced pressure, etc.). The dispersant after concentration can be identified and its molecular weight measured by the above-mentioned method.

<Method for producing dried cellulose fiber body>
Another aspect of the present invention provides a method for producing the dried cellulose fiber body of the present disclosure, the method including 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 the dried cellulose fiber body.

(Slurry preparation process)
In this step, a slurry containing cellulose fibers and a liquid medium is prepared. As the liquid medium, the above-mentioned water-miscible organic solvent can be suitably used. 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 process efficiency in the subsequent drying step, and is preferably 60% by mass or less, or 55% by mass or less, or 50% by mass or less, or 45% by mass or less from the viewpoint of maintaining good handleability by avoiding excessive increase in the viscosity of the slurry and solidification due to aggregation. For example, the production of cellulose nanofibers is often carried out in a dilute dispersion, and the cellulose fiber concentration in the slurry may be adjusted to the preferred range by concentrating such a dilute dispersion. For concentration, methods such as suction filtration, pressure filtration, centrifugal deliquation, and heating can be used.

(Drying process)
In this step, the slurry is dried under controlled drying conditions to form a dried cellulose fiber body. When the dried cellulose fiber body contains cellulose fibers and additional components, the additional components may be added before, during, and/or after drying of the cellulose fiber slurry. For drying, a drying device that enables the above drying speed, such as a spray dryer or an extruder, can be used. The drying device may be a commercially available product, and examples of the drying device include a micromist spray dryer (manufactured by Fujisaki Electric Co., Ltd.), a spray dryer (manufactured by Okawara Kakoki Co., Ltd.), and a twin-screw extruder (manufactured by Japan Steel Works, Ltd.). Among the drying conditions, controlling the drying speed, drying temperature, and/or pressure (degree of reduced pressure), especially the drying speed, is useful for producing the dried cellulose fiber body of the present disclosure.

The drying speed, which is the amount (parts by mass) of liquid medium desorbed per minute per 100 parts by mass of the slurry, may be, for example, 10%/min or more, or 50%/min or more, or 100%/min or more, from the viewpoint of forming a dried cellulose fiber body of a desired particle size by rapidly drying the slurry, and may be, for example, 10,000%/min or less, or 1,000%/min or less, or 500%/min or less, from the viewpoint of suppressing aggregation of the cellulose fibers by avoiding excessive pulverization of the cellulose fibers and obtaining good handleability. The drying speed is calculated by the following formula:
Drying rate (%/min) = (water content of slurry at the start of drying (% by mass) - water content of dried body at the end of drying (% by mass)) / time required from the start of drying to the end of drying (min)
(i.e., the average value throughout the drying process).
Here, the start of drying refers to the time when the process of supplying the slurry or cake to be dried to the device and drying at the intended drying temperature, degree of vacuum, and shear rate begins, and the time for premixing under conditions where the drying temperature, degree of vacuum, and shear rate are different from those in the drying process is not included in the drying time.
The end point of drying refers to the time when the moisture content first becomes 7% by mass or less when sampling is performed at intervals of at most 10 minutes from the start of drying.
In the case of a continuous drying device, 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. In addition, when an extruder is used as a drying device, the residence time can be calculated from the screw rotation speed and the total pitch number of the screw.

The drying temperature may be, for example, 20°C or more, or 30°C or more, or 40°C or more, or 50°C or more from the viewpoints of drying efficiency and of appropriately agglomerating the cellulose fibers to form a dried cellulose fiber body of a desired particle size, and may be, for example, 200°C or less, or 150°C or less, or 140°C or less, or 130°C or less, or 100°C or less from the viewpoints of preventing thermal deterioration of the cellulose fibers and additional components 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, as the surface temperature of the temperature-regulating jacket of the drying device, 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, or -10 kPa or less, or -20 kPa or less, or -30 kPa or less, or -40 kPa or less, or -50 kPa or less from the viewpoint of drying efficiency and of appropriately agglomerating the cellulose fibers to form a dried cellulose fiber body of a desired particle size, and may be -100 kPa or more, or -95 kPa or more, or -90 kPa or more from the viewpoint of avoiding excessive pulverization of the cellulose fibers.

In the drying step, the residence time of the slurry at a temperature of 20°C to 200°C may be set to preferably 0.01 to 10 minutes, or 0.05 to 5 minutes, or 0.1 to 2 minutes. Drying under such conditions rapidly dries the cellulose fibers, and successfully produces dried cellulose fibers of the desired particle size.

For example, when using a spray dryer, the slurry is sprayed and introduced into a drying chamber through which hot gas is circulated using a spray mechanism (rotating disk, pressurized nozzle, etc.) and dried. The size of the slurry droplets when sprayed may be, for example, 0.01 μm to 500 μm, or 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, etc. The hot gas temperature may be, for example, 50°C to 300°C, or 80°C to 250°C, or 100°C to 200°C. The contact between the slurry droplets and the hot gas in the drying chamber may be parallel, counter, or parallel. The particulate cellulose fiber dried body produced by drying the droplets is collected using a cyclone, drum, etc.

For example, when an extruder is used, the slurry is fed from a hopper into a kneading section equipped with a screw, and the slurry is dried by continuously transporting the slurry with the screw in the kneading section under reduced pressure and/or heating. The screw may be a combination of a conveying screw, a counterclockwise screw, and a kneading disk in any order. The drying temperature may be, for example, 50°C to 300°C, or 80°C to 250°C, or 100°C to 200°C.

<Method for producing resin composite>
One aspect of the present invention provides a method for producing a resin composite containing cellulose fibers and a resin, the method comprising mixing the dried cellulose fiber material of the present disclosure as described above with a resin.

<Resin>
The resin may be a thermoplastic resin, a thermosetting resin, or a photocurable resin. The resin may be an elastomer. From the viewpoints of moldability and productivity, a thermoplastic resin is more preferable.

(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, etc. The melting point of the thermoplastic resin can be, for example, 150°C to 190°C or 160°C to 180°C for a resin with a relatively low melting point (e.g., a polyolefin resin), or 220°C to 350°C or 230°C to 320°C for a resin with a relatively high melting point (e.g., a polyamide resin).

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

Polyolefin resins that are preferred 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 (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 (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.

Here, the most preferred polyolefin resin is polypropylene. In particular, polypropylene having a melt mass flow rate (MFR) of 3 g/10 min or more and 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. It is desirable that the MFR does not exceed the above upper limit from the viewpoint of improving the toughness of the resin composite, and it is desirable that the MFR does not exceed the above lower limit from the viewpoint of the fluidity of the resin composite.

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

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

Preferred polyamide resins as thermoplastic resins include: polyamides obtained by polycondensation reaction of lactams (e.g., polyamide 6, polyamide 11, polyamide 12, etc.); diamines (e.g., 1,6-hexanediamine, 2-methyl-1,5-pentanediamine, 1,7-heptanediamine, 2-methyl-1-6-hexanediamine, 1,8-octanediamine, 2-methyl-1,7-heptanediamine, 1,9-nonanediamine, 2-methyl-1,8-octanediamine, 1,10-decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine, m-xylylenediamine, etc.) and dicarboxylic acids (e.g., butanedioic acid, pentanedioic acid, hexanedioic acid, Polyamides obtained as copolymers with heptanedioic acid, octanedioic acid, nonanedioic acid, decanedioic acid, benzene-1,2-dicarboxylic acid, benzene-1,3-dicarboxylic acid, benzene-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid, cyclohexane-1,4-dicarboxylic acid, etc. (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 in which these are copolymerized (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, or 250°C or higher, and from the viewpoint of ease of manufacturing the resin composite, the melting point is preferably 350°C or lower, or 320°C or lower, or 300°C or lower.

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

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

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

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

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

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

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

Preferred polyester resins as thermoplastic resins include one or more selected from polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), polyhydroxyalkanoic acid (PHA), polylactic acid (PLA), polyarylate (PAR), etc. Among these, PET, PBS, PBSA, PBT, and PEN are more preferable, and PBS, PBSA, and PBT are particularly preferable.

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

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

(Thermosetting resin)
Examples of the thermosetting resin 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, aryl alkylene type epoxy resin, tetraphenylolethane type epoxy resin, naphthalene type epoxy resin, anthracene type epoxy resin, phenoxy type epoxy resin, dicyclopentadiene type epoxy resin, norbornene type epoxy resin, adamantane type epoxy resin, fluorene type epoxy resin, glycidyl methacrylate copolymer epoxy resin, cyclohexylmaleimide and glycidyl methacrylate copolymer epoxy resin, epoxy modified polybutadiene rubber derivative, CTBN modified epoxy resin, trimethylolpropane polyglycidyl ether, Phenyl-1,3-diglycidyl ether, biphenyl-4,4'-diglycidyl ether, 1,6-hexanediol diglycidyl ether, diglycidyl ether of ethylene glycol or propylene glycol, sorbitol polyglycidyl ether, tris(2,3-epoxypropyl)isocyanurate, triglycidyl tris(2-hydroxyethyl)isocyanurate, novolac-type phenolic resins such as phenol novolac resin, cresol novolac resin, and bisphenol A novolac resin, unmodified resol phenolic resin, paulownia wood Examples of the resin include phenolic resins such as resol-type phenolic resins, such as oil-modified resol phenolic resins modified with oil, linseed oil, walnut oil, etc.; triazine ring-containing resins, such as phenoxy resins, urea (urea) resins, and melamine resins; unsaturated polyester resins, bismaleimide resins, diallyl phthalate resins, silicone resins, resins having a benzoxazine ring, norbornene 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 radical reaction types in which a monomer reacts with radicals generated by light, and cationic reaction types in which a monomer undergoes cationic polymerization, according to the reaction mechanism. Examples of radical reaction type monomers include (meth)acrylate compounds, vinyl compounds (e.g., certain vinyl ethers), and the like. Examples of cationic reaction types include epoxy compounds, certain vinyl ethers, and the like. For example, an epoxy compound that can be used as a cationic reaction type can be a monomer for both thermosetting resins and photocurable resins.

A (meth)acrylate compound is a compound that has one or more (meth)acrylate groups in the 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 ether, 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 methyl styrene and ethyl styrene. Other examples of vinyl compounds include triallyl isocyanurate and trimethallyl isocyanurate.

As a raw material for the photocurable resin, so-called reactive oligomers may be used. Examples of reactive oligomers include oligomers that have any combination selected from (meth)acrylate groups, epoxy groups, urethane bonds, and ester bonds in the same molecule, such as urethane acrylates that have (meth)acrylate groups and urethane bonds in the same molecule, polyester acrylates that have (meth)acrylate groups and ester bonds in the same molecule, and epoxy acrylates derived from epoxy resins that have epoxy groups and (meth)acrylate groups in the same molecule.

(Elastomer)
Examples of elastomers (i.e., rubber) 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, polysulfide rubber, silicone rubber, fluororubber, urethane rubber, and the like.

When the resin is a thermoplastic resin, the cellulose fiber (which may be in the form of a dried body of the present disclosure or a redispersion obtained by dispersing the dried body in a dispersion medium) can be melt-kneaded with the thermoplastic resin to produce a resin composite.
- A method in which a resin monomer is mixed with cellulose fibers, a polymerization reaction is carried out, the resulting resin composite is extruded into a strand shape, and cooled and solidified in a water bath to obtain a pellet-shaped molded product;
A method in which a mixture of resin and cellulose fibers is melt-kneaded using a single-screw or twin-screw extruder, extruded into a strand shape, and cooled and solidified in a water bath to obtain a pellet-shaped molded product;
A method in which a mixture of resin and cellulose fibers is melt-kneaded using a single-screw or twin-screw extruder, extruded into a rod or tube, and cooled to obtain an extrusion molded product;
A method in which a mixture of resin and cellulose fibers is melt-kneaded using a single-screw or twin-screw extruder and extruded through a T-die to obtain a sheet or film-like molded product;
In a preferred embodiment, a mixture of resin and cellulose fibers is melt-kneaded using a single-screw or twin-screw extruder, extruded into a strand shape, and cooled and solidified in a water bath to obtain a pellet-shaped molded product.
A specific example of a method for melt-kneading a resin and cellulose fibers is a method in which a resin and cellulose fibers transported in a desired ratio are mixed together and then melt-kneaded.

For melt kneading, an extruder such as a single screw extruder or a twin screw extruder can be used, but a twin screw extruder is preferred in terms of controlling the dispersibility of the cellulose fibers. The ratio L/D, obtained by dividing the cylinder length (L) of the extruder by the screw diameter (D), is preferably 30 or more, and particularly preferably 40 or more. 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 in the extruder cylinder is optimized by combining an elliptical two-blade screw-shaped conveying screw, a kneading element called a kneading disk, and other components.

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°C-190°C for polyacetal resin, and 160-180°C for polypropylene. The heating temperature setting is preferably in the range of 20°C higher than these recommended minimum processing temperatures. By setting the mixing temperature within this temperature range, the cellulose fibers and resin can be mixed uniformly.

Resin composites containing thermoplastic resins as resins can be provided in various shapes. Specifically, resin pellets, sheets, fibers, plates, rods, etc. can be mentioned, but the resin pellet shape is more preferable from the viewpoint of ease of post-processing and ease of transportation. Preferred pellet shapes in this case include round, elliptical, cylindrical, etc., which differ depending on the cutting method used during extrusion processing. Pellets cut by a cutting method called underwater cutting are often round, pellets cut by a cutting method called hot cutting are often round or elliptical, and pellets cut by a cutting method called strand cutting are often cylindrical. In the case of round pellets, the preferred size is a pellet diameter of 1 mm or more and 3 mm or less. In the case of cylindrical pellets, the preferred diameter is 1 mm or more and 3 mm or less, and the preferred length is 2 mm or more and 10 mm or less. It is desirable to set the above diameter and length to the lower limit or more from the viewpoint of operational stability during extrusion, and it is desirable to set them to the upper limit or less from the viewpoint of bite into the molding machine in post-processing.

Resin composites containing a thermoplastic resin as the resin can be used as various resin molded products. There are no particular limitations on the manufacturing method for the resin molded products, and any manufacturing method can be used, including injection molding, extrusion molding, blow molding, inflation molding, and foam molding. Of these, injection molding is the most preferable from the standpoint of design and cost.

When the resin is a thermosetting resin or a photocurable resin, the resin composite can be produced by, for example, a method of thoroughly dispersing cellulose fibers in a resin solution or resin powder dispersion and drying the resulting mixture, a method of thoroughly dispersing cellulose fibers in a resin monomer liquid and polymerizing the resulting mixture by heat, UV irradiation, a polymerization initiator, etc., a method of thoroughly impregnating a dried cellulose fiber body with a resin solution or resin powder dispersion and drying the resulting mixture, or a method of thoroughly impregnating a dried cellulose fiber body with a resin monomer liquid and polymerizing the resulting mixture by heat, UV irradiation, a polymerization initiator, etc. When curing the resulting mixture, various polymerization initiators, curing agents, curing accelerators, polymerization inhibitors, etc. can be added.

When the resin is a thermosetting resin or a photocurable resin, a method may be used in which an uncured or semi-cured sheet called a prepreg is prepared, the prepreg is then made into a single layer or laminated, and the resin is cured and molded by applying pressure and heat. Methods for applying pressure and heat include press molding, autoclave molding, bagging molding, wrapping tape method, and internal pressure molding.

When the resin is a photocurable resin, the resin composite can be produced using various curing methods that use active energy rays.

When the resin is an elastomer, a resin composite can be produced by a method of dry kneading dried cellulose fibers with raw rubber, or a method of dispersing or dissolving cellulose fibers and raw rubber in a dispersion medium, then drying and mixing. As a mixing method, a mixing method using a homogenizer is preferable because it can apply high shear force and pressure and promote dispersion, but other methods such as a propeller stirrer, rotary stirrer, electromagnetic stirrer, and manual stirring can also be used. A resin composite containing an elastomer can be molded using a desired molding method such as mold molding, injection molding, extrusion molding, hollow molding, and foam molding to obtain an unvulcanized molded product in the desired shape such as a sheet, pellet, or powder. The unvulcanized molded product can be vulcanized by heat treatment or the like as necessary to obtain a resin composite.

A resin composite containing a thermoplastic resin or elastomer may be partially (e.g., several locations) melted by heat treatment and then bonded to, for example, a resin or metal substrate. The resin composite may be a coating applied to a resin or metal substrate, or may form a laminate with the substrate. Furthermore, sheet-, film-, or fiber-shaped resin composites may be subjected to secondary processing such as annealing, etching, corona treatment, plasma treatment, embossing transfer, cutting, and surface polishing.

In the resin composite, the amount of cellulose fibers per 100 parts by mass of resin may be, from the viewpoint of the balance between processability and mechanical properties, 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, and may be 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.

In one embodiment, the tensile elongation at break of the resin composite can be 5% or more, or 8% or more, or 10% or more. In one embodiment, from the viewpoint of ease of manufacturing the resin composite, the tensile elongation at break can be 200% or less, or 100% or less, or 50% or less.

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

<Production 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 in 30 parts by mass of dimethyl sulfoxide (DMSO) at room temperature for 1 hour at 500 rpm using a single-shaft stirrer (DKV-1 φ125 mm dissolver manufactured by Imex Co., Ltd.). The mixture was then fed to a bead mill (NVM-1.5 manufactured by Imex Co., Ltd.) using a hose pump, and circulated for 180 minutes using only DMSO to obtain a slurry S1 (DMSO solvent) with a solid content of 3.2% by mass as a fine cellulose fiber slurry.

During circulation operation, the rotation speed of the bead mill was 2500 rpm, the peripheral speed was 12 m/s, the beads used were made of zirconia, had a diameter of 2.0 mm, and a filling rate of 70% (the slit gap of the bead mill was 0.6 mm). During circulation operation, the slurry temperature was controlled at 40°C using a chiller to absorb heat generated by friction.

After the slurry S1 was placed in 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 temperature inside the tank was raised 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 was added and thoroughly stirred, and then the mixture was placed in a dehydrator and concentrated. The resulting wet cake was dispersed again in 30 parts by mass of pure water, stirred, and concentrated, and this washing procedure was repeated a total of five times to remove unreacted reagents and solvent, and 10 parts by mass of acetylated fine cellulose fiber cake (CNF-B cake) (water solvent) with a solids content of 10% by mass was obtained. A porous sheet was made from this cake and the degree of acyl substitution (DS) was determined, which was DS = 1.0.

[CNF-C] (CNF processed with a disc refiner)
3 parts by mass of cotton linter pulp was 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 (30 parts by mass) containing water. Next, 170 parts by mass of water was added to 30 parts by mass of purified pulp containing water to disperse it in water (solid content rate 1.5% by mass), and the aqueous dispersion was beaten for 20 minutes with a clearance between disks of 1 mm using an SDR14 type lab refiner (pressure type DISK type) manufactured by Aikawa Iron Works Co., Ltd. as a disk refiner device. Then, the solid content rate was concentrated to 10% by mass using a dehydrator to obtain a CNF-C cake (water solvent).

[CNF-D] (CNF-C further defibrated using a high-pressure homogenizer)
The CNF-C cake was thoroughly beaten under conditions that reduced the clearance to a level close to zero, to obtain a beaten water dispersion (solid content concentration: 1.5% by mass). The obtained beaten water dispersion was directly subjected to a high-pressure homogenizer (NSO15H manufactured by Niro Soavi (Italy)) for 15 cycles under an operating pressure of 100 MPa to obtain a cellulose fiber slurry (solid content concentration: 1.5% by mass). The resulting mixture was then concentrated to a solid content of 10% by mass using a dehydrator to obtain a CNF-D cake (water solvent).

[CNF-E] (acetylated CNF)
CNF-B was produced in the same manner as CNF-B, except that the reaction time was 60 minutes. A porous sheet was produced from this cake, and the degree of acyl substitution (DS) was determined, which was DS = 0.5.

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

<Dispersant>
Polyethylene oxide-polypropylene oxide copolymer (PEG-PPG) (Sanyo Chemical Industries, Ltd.: GL-3000)

<Production of dried cellulose fiber>
A dispersant was added to the cellulose fiber cake (solid content 10% by mass) in an amount of 43 parts by mass relative to 100 parts by mass of cellulose solid content, and the mixture was thoroughly stirred to obtain a cellulose fiber cake containing the dispersant (for products other than MMSD, described below). Alternatively, the cellulose fiber cake (solid content 10% by mass) was diluted with distilled water to a solid content of 1% by mass, and then a dispersant was added in an amount of 43 parts by mass relative to 100 parts by mass of cellulose solid content, and the mixture was thoroughly stirred to obtain a cellulose fiber slurry (for MMSD, described below). These were put into a drying device 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 moisture meter (MX-50 (manufactured by A&D)), and the time when the moisture content became 7% by mass or less (93% by mass or more of solid content) was defined as the end point of drying. The conditions were as follows.

[Loedige Mixer (LM)]
Equipment: Lödige mixer (model number: VT-20) manufactured by Chuo Kiko Co., Ltd.
Conditions: Jacket temperature 100° C., agitation with an agitator (circumferential speed 1 m/s) and a chopper (3000 rpm) was performed while reducing the pressure to −90 kPa with a vacuum pump. Drying under reduced pressure was performed until the product temperature reached 50° C.
The clearance was measured as the minimum distance between the chopper (diameter 100 mm) and the jacket.
The drying time under these conditions was 160 minutes.
The surface temperature of the jacket was measured at three points, and the average value was used as the drying temperature.

[High Speed Vacuum Dryer (HSVD)]
Equipment: High-speed vacuum dryer manufactured by EarthTechnica Corporation (model number: FS10)
Conditions: Jacket temperature 70° C., agitation with an agitator (circumferential speed 2 m/s) and a chopper (3500 rpm) was performed while reducing the pressure to −70 kPa with a vacuum pump. Drying under reduced pressure was performed until the product temperature reached 60° C.
The clearance was measured as the minimum distance between the chopper (diameter 100 mm) and the agitator.
The drying time under these conditions was 180 minutes.
The surface temperature of the jacket was measured at three points, and the average value was used as the drying temperature.

[FM Mixer (HM)]
Equipment: FM mixer (model: FM20) manufactured by Nippon Coke & Engineering Co., Ltd.
Conditions: Jacket temperature 80° C., stirring with a stirring blade (500 rpm) was performed while reducing the pressure to −70 kPa with a vacuum pump. Drying under reduced pressure was performed until the product temperature reached 70° C.
The clearance was measured as the minimum distance between the upper stirring blade (diameter 400 mm) and the jacket.
The drying time under these conditions was 180 minutes.
The surface temperature of the jacket was measured at three points, and the average value was used as the drying temperature.

[Paddle dryer (PD)]
Equipment: Paddle dryer manufactured by Nara Machinery Co., Ltd. (Model number: NPD-1.6W-12L)
Conditions: heating steam temperature 120°C, drying was carried out while stirring with a stirring blade (30 rpm) until the product temperature reached 100°C.
The clearance was measured as the minimum distance between the stirring blade (diameter 250 mm) and the jacket.
The drying time under these conditions was 50 minutes.
The surface temperature of the stirring blade through which heated steam was circulated was measured at three points, and the average value was used as the drying temperature.

[Micro Mist Spray Dryer (MMSD)]
Equipment: Fujisaki Electric Co., Ltd. Micro Mist Spray Dryer (Model: MDL050-M)
Conditions: The cellulose fiber slurry was dried at an inlet temperature of 200° C., an air supply volume of 1 m ³ /min, a nozzle air flow rate of 80 NL/min, and a slurry volume of 50 mL/min, and the dried powder was collected in a cyclone collector.
In this apparatus, since it does not have a stirring mechanism or the like, it is assumed that no shear rate is generated.
The drying time and residence time in this condition was 1 minute.
The inlet temperature of the hot air was measured three times during the drying process, and the average value was used as the drying temperature.

[Twin-screw extruder (Ex-dry)]
Equipment: Twin-screw extruder manufactured by Japan Steel Works, Ltd. (Model: TEX54αIII: L/D=63)
Conditions: cylinder temperature 200° C., while the screw was rotating at 66 rpm, the raw material was fed to the uppermost barrel at 20 kg/h using a gravimetric feeder, and a dry powder was obtained from the discharge port.
The clearance was measured as the minimum distance between the kneading disc (diameter 54 mm) and the cylinder.
The drying time and residence time in this condition was 1 minute.
The temperature of the cylinder in which the most downstream kneading disk is disposed was measured three times, and the average value was used as the drying temperature.

[Planetary Mixer (PM)]
Equipment: Planetary mixer manufactured by Kodaira Manufacturing Co., Ltd. (Model: ACM-5LVT: hook type)
Conditions: Jacket temperature 60° C., stirring at 307 rpm, pressure reduced to −90 kPa with a vacuum pump. Reduced pressure drying was carried out until the product temperature reached 50° C.
The clearance was measured as the minimum distance between the hook fin (diameter 100 mm) and the jacket.
The drying time under these conditions was 180 minutes.
The surface temperature of the jacket was measured at three points, and the average value was used as the drying temperature.

[Examples 1 to 12, Comparative Example 8]
A dried cellulose fiber body was obtained using the CNF shown in Table 1 and the above-mentioned apparatus shown in Table 2 with the CNF, drying temperature, and shear rate shown in Tables 3 and 4. Note that for Example 12, a cellulose fiber slurry was obtained without using a dispersant in the preparation of the raw material.

<Production of resin composite>
The dried cellulose fiber produced above and a thermoplastic resin (UBE nylon 1013B manufactured by Ube Industries, Ltd.) were mixed in such a ratio that the cellulose fiber accounted for 10 mass % of the resin composite, and a resin composite was produced according to the following procedure.

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

As for the screw configuration, cylinders 1 to 3 were used as a conveying zone consisting of only a conveying screw, and two clockwise kneading discs (feed type kneading discs: hereinafter sometimes simply referred to as RKDs) and two neutral kneading discs (non-conveying type kneading discs: hereinafter sometimes simply referred to as NKDs) were arranged in order from the upstream side in cylinder 4. Cylinder 5 was used as a conveying zone, one RKD and two subsequent NKDs were arranged in cylinder 6, cylinders 7 and 8 were used as conveying zones, and two NKDs were arranged in cylinder 9. The following cylinder 10 was used as a conveying zone, and two NKDs and one subsequent counterclockwise screw were arranged in cylinder 11, and cylinders 12 and 13 were used as conveying zones. A vent port was installed at the top of cylinder 12 to enable reduced pressure suction, and vacuum suction was performed.

The dried cellulose fiber was mixed with a thermoplastic resin, melt-kneaded at 250 rpm using a twin-screw extruder, extruded into strands, cooled with water, cut, and obtained as pellets. The resulting pellets were melted at 260°C using an attached injection molding machine, and dumbbell-shaped test pieces according to JIS K7127 were prepared and used for evaluation.

Evaluation
<Evaluation of Cellulose Fibers>
[Preparation of porous sheet]
First, the wet cake was added to tert-butanol, and further dispersed in a mixer or the like until no aggregates were formed. The concentration was adjusted to 0.5% by mass per 0.5 g of cellulose fiber solids. 100 g of the obtained tert-butanol dispersion was filtered on filter paper, dried at 150°C, and then the filter paper was peeled off to obtain a sheet. The sheet with an air resistance of 100 sec/100 ml or less per 10 g/ ^m2 sheet basis weight was used as a porous sheet and was used as a measurement sample.
After measuring the basis weight W (g/ ^m2 ) of the sample left to stand for one day in an environment of 23°C and 50% RH, the air resistance R (sec/100 ml) was measured using an Oken type air resistance tester (manufactured by Asahi Seiko Co., Ltd., model EG01). At this time, the value per basis weight of 10 g/ ^m2 was calculated according to the following formula.
Air resistance per unit area of 10 g/ ^m2 (sec/100 ml) = R/W x 10

[Degree of acyl substitution (DS)]
The infrared spectrum of the porous sheet at five points was measured by an ATR-IR method using a Fourier transform infrared spectrophotometer (FT/IR-6200 manufactured by JASCO Corp.) The infrared spectrum measurement was performed under the following conditions.
Number of times: 64
Wave number resolution: ⁴ cm
Measurement wave number range: 4000 to 600 cm ^-1 ,
ATR crystal: Diamond,
Incident angle: 45°
From the obtained IR spectrum, the IR index was calculated according to the following formula (1):
IR index = H1730/H1030 (1)
In the formula, H1730 and H1030 are the absorbances at 1730 cm ^-1 and 1030 cm ^-1 (absorption bands of C-O stretching vibration of the cellulose backbone chain). However, the lines connecting 1900 cm ^-1 and 1500 cm ^-1 and the line connecting 800 cm ^-1 and 1500 cm ^-1 are taken as baselines, and the absorbances are calculated based on these baselines as 0 absorbance.
Then, the average degree of substitution at each measurement location was calculated from the IR index according to the following formula (2), and the average value was taken as DS.
DS = 4.13 × IR index (2)

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

[Average fiber diameter]
The cellulose fiber cake or cellulose fiber slurry was diluted with tert-butanol to 0.01% by mass, dispersed using a high-shear homogenizer (manufactured by IKA, product name "Ultra Turrax T18") under processing conditions of 25,000 rpm for 5 minutes, cast onto mica, air-dried, and measured using a high-resolution scanning electron microscope. The measurement was performed by adjusting the magnification so that at least 100 cellulose fibers were observed, the major axis (L) of 100 randomly selected cellulose fibers was measured, and the arithmetic 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 the porous sheet was weighed, cut into small pieces with scissors, lightly stirred, and then 20 mL of pure water was added and left for one day. Next, water and solids were separated by centrifugation. Then, 20 mL of acetone was added, lightly stirred, and left for one day. Next, acetone and solids were separated by centrifugation. Then, 20 mL of N,N-dimethylacetamide was added, lightly stirred, and left for one day. N,N-dimethylacetamide and solids were separated again by centrifugation, and then 20 mL of N,N-dimethylacetamide was added, lightly stirred, and left for one day. N,N-dimethylacetamide and solids were separated by centrifugation, and 19.2 g of N,N-dimethylacetamide solution prepared so that lithium chloride was 8 mass percent was added to the solids, and the mixture was stirred with a stirrer, and it was confirmed that the solids had dissolved. The solution in which the cellulose fibers were dissolved was filtered through a 0.45 μm filter, and the filtrate was used as a sample for gel permeation chromatography. The apparatus and measurement conditions used are as follows.
Equipment: Tosoh HLC-8120
Column: TSKgel SuperAWM-H (6.0 mm ID x 15 cm) x 2 Detector: RI detector Eluent: N,N-dimethylacetamide (lithium chloride 0.2%)
Flow rate: 0.6 mL/min. Calibration curve: Pullulan equivalent

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

<Evaluation of dried cellulose fiber body>
The measurements were carried out using a powder tester (model number: PT-X) manufactured by Hosokawa Micron Corporation.

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

[Collapse angle]
A 109 g weight placed on the same base as the measurement table was dropped three times at intervals of two seconds onto the sample for which the angle of repose was measured, from a height of 160 mm, and then the conical shape of the sample was photographed from the side, and the angle between the generatrix of the cone and the horizontal plane was measured. The number average value of the three measurements was taken as the angle of collapse.

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

[Loose bulk density]
The dried cellulose fiber was poured into a 100 mL (inner diameter 50.46 mm × depth 50 mm) stainless steel bottomed cylindrical container at 10 g/min with a medicine spoon until it overflowed, and the dried cellulose was drained off and then weighed to the nearest 0.01 g. The number average value of the weight measured three times was divided by the internal volume of the bottomed cylindrical container to calculate the loose bulk density.

[Collected bulk density]
A resin adapter (inner diameter 50.46 mm x length 40 mm) of sufficient capacity was connected to the top of the same bottomed cylindrical container used for the loose bulk density so that it was in close contact with the container, and the dried cellulose fiber was poured into the container until it overflowed using the same procedure as for the measurement of the loose bulk density. The bottomed cylindrical container was then subjected to vibration with an amplitude of 1.5 mm and 50 Hz for 30 seconds using a motor with an eccentric weight attached to the rotating shaft while the adapter was still connected. The adapter was then removed, and the dried material was drained to the level, after which its weight was measured to the nearest 0.01 g. The number average value of the weight measured three times was divided by the internal volume of the bottomed cylindrical container to calculate the collected bulk density.

[Compression level]
From the values of the packed bulk density and the loose bulk density, the following formula:
The degree of compression was calculated according to the formula: Compressibility=(Packed bulk density-Loose bulk density)/Packed bulk density.

[Moisture percentage]
The measurements were carried out 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 receiver in the order of 710 μm, 1000 μm, and 1700 μm mesh, and a precisely weighed dried cellulose fiber material in the range of 1 to 20 g was placed on the top sieve, followed by vibration at an amplitude of 1.5 mm and 50 Hz for 10 minutes. The fractionated sample was then precisely weighed together with the sieve, and the weight fraction of each fraction was calculated to obtain a particle size distribution.

[Screen mesh evaluation]
With a 50-mesh screen mesh attached between the die adaptor 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 on the following three-level scale.
A: Almost no particles were trapped. B: Some particles were trapped, and the screen mesh needed to be replaced. C: The die pressure rose before the operation was completed, and the screen mesh needed to be replaced.

<Evaluation of Resin Composite>
[Tensile elongation at break, bending modulus]
The obtained pellets were molded using an injection molding machine under conditions in accordance with JIS K6920-2 to form multipurpose test pieces in accordance with ISO294-3.
The multipurpose test specimens were measured for tensile elongation at break in accordance with ISO 527 and for flexural modulus in accordance with ISO 179. Since polyamide resins change due to moisture absorption, they were stored in aluminum moisture-proof bags immediately after molding to suppress moisture absorption.
The results are shown in Table 1.

The highly tough resin composites that the present invention can provide can be suitably used in a variety of resin molding applications.

Claims (17)

A cellulose fiber dry body containing chemically modified cellulose fibers,
the chemical modification is esterification,
The cellulose fibers have a number average fiber diameter of 2 nm to 1000 nm,
the dried cellulose fiber material has an angle of repose of 40° to 60°, a difference angle of 10° or less, a loose bulk density of 0.01 g/cm ³ to 0.40 g/cm ³ , a packed bulk density of 0.1 g/cm ³ to 0.55 g/cm ³ , and a compressibility of 20% to 40%,
In the dried cellulose fiber material, the content of particle components having a particle size of 710 μm or less is 50% by mass to 90% by mass. The dried cellulose fiber material according to claim 1 , wherein the esterification is acetylation. The dried cellulose fiber material according to claim 1 or 2 , wherein the average degree of substitution (DS) of the cellulose fiber is 0.1 to 1.2. A dried cellulose fiber material comprising cellulose fibers and a dispersant,
The cellulose fibers have a number average fiber diameter of 2 nm to 1000 nm,
the dried cellulose fiber material has an angle of repose of 40° to 60°, a difference angle of 10° or less, a loose bulk density of 0.01 g/cm ³ to 0.40 g/cm ³ , a packed bulk density of 0.1 g/cm ³ to 0.55 g/cm ³ , and a compressibility of 20% to 40%,
In the dried cellulose fiber material, the content of particle components having a particle size of 710 μm or less is 50% by mass to 90% by mass. The dried cellulose fiber material according to claim 4 , 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. The dried cellulose fiber material according to any one of claims 1 to 5 , wherein the content of particulate components having a particle size of more than 710 µm and not more than 1000 µm is 10% by mass to 30% by mass. The dried cellulose fiber material according to any one of claims 1 to 6 , wherein the content of particle components having a particle size of more than 1000 µm is 1% by mass to 10% by mass. The dried cellulose fiber material according to any one of claims 1 to 7 , wherein the cellulose fiber has an average fiber length (L)/fiber diameter (D) ratio of 30 to 5,000. The cellulose fiber dried material according to any one of claims 1 to 8 , 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 dried cellulose fiber material according to any one of claims 1 to 9 , wherein the cellulose fibers have a crystallinity of 60% or more. The dried cellulose fiber material according to any one of claims 1 to 10 , wherein the cellulose fiber has an alkali-soluble polysaccharide content of 20 mass% or less. The dried cellulose fiber material according to any one of claims 1 to 11 , having a moisture content of 30 mass% or less. A method for producing a dried cellulose fiber material according to any one of claims 1 to 12 ,
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 10,000%/min to form a dried cellulose fiber body.
A method comprising: 14. The method of claim 13 , wherein the drying step is carried out in a continuous process with a residence time of 0.01 minutes to 10 minutes at a drying temperature of 20°C to 200°C. A method for producing a resin composite containing cellulose fibers and a resin, comprising:
The method includes mixing the dried cellulose fiber material according to any one of claims 1 to 12 with a resin,
The resin composite has a tensile elongation at break of 8% or more. The method of claim 15 , wherein the resin is a thermoplastic resin. The method of claim 16 , wherein the thermoplastic resin is a polyamide-based resin.

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