JP7547040B2 - Fine cellulose fiber and resin composite - Google Patents

Description

The present invention relates to fine cellulose fibers and a resin composite.

Thermoplastic resins are lightweight and have excellent processability, so they are widely used in a wide range of applications, including automotive parts, electrical and electronic parts, office equipment housings, and precision parts. However, resin alone often lacks sufficient mechanical properties and dimensional stability, so composites of resin and various fibrous materials are commonly used.

In recent years, nanofibers, including fine cellulose fibers (also called cellulose nanofibers (CNF)), have come to be used as fibrous materials. CNF has a tendency to aggregate in a dry state, so it is manufactured as an aqueous dispersion that allows for stable dispersion.

Various techniques for dispersing cellulose fibers in other materials have been proposed in the past. For example, Patent Document 1 describes a composition containing cellulose nanofibers and a block copolymer with the aim of improving the dispersibility of cellulose in resin, and Patent Document 2 describes a resin composition containing polyvinyl alcohol, polyvinylpyrrolidone, and a water-soluble resin consisting of a copolymer of these with the aim of dispersing cellulose fibers with a high aspect ratio well in a resin composition.

Patent No. 6234037 JP 2012-236906 A

However, even with the above-mentioned conventional techniques, it is still difficult to disperse fine cellulose fibers sufficiently well in the resin. In particular, once agglomerates form in fine cellulose fibers, it is difficult to eliminate the agglomerates, and these agglomerates cause a significant decrease or non-uniformity in the physical properties of the resin composite in which fine cellulose fibers are dispersed in the resin.

The present invention aims to solve the above problems and provide fine cellulose fibers that are less likely to form agglomerates and have a good effect of improving the physical properties of resin composites.

As a result of intensive research into solving the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by controlling the sedimentation behavior of fine cellulose fibers in a dilute dispersion of a specific concentration, and thus completed the present invention.
That is, the present invention includes the following aspects.
[1] A fine cellulose fiber,
The fine cellulose fibers have a ratio of the sedimentation height of the fine cellulose fibers to the total liquid height of the test dispersion (100%) of 6% or more when the test dispersion containing the fine cellulose fibers in water at a concentration of 0.05% by mass is allowed to stand at 23°C and normal pressure for 24 hours.
[2] The fine cellulose fibers according to the above aspect 1, having an average fiber diameter of 2 to 1000 nm.
[3] The fine cellulose fibers according to the above aspect 1 or 2, which are chemically modified.
[4] The fine cellulose fibers according to the above aspect 3, wherein the chemical modification is acylation.
[5] The fine cellulose fiber according to any one of the above aspects 1 to 4, having a weight average molecular weight (Mw) of 100,000 or more and a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of 6 or less.
[6] The fine cellulose fibers according to any one of the above aspects 1 to 5, having an average alkali-soluble polysaccharide content of 12% by mass or less and a crystallinity of 60% or more.
[7] A dried body comprising the fine cellulose fibers according to any one of aspects 1 to 6.
[8] The dried body according to aspect 7, having a moisture content of 50% by mass or less.
[9] A resin composite comprising the fine cellulose fiber according to any one of aspects 1 to 6 above and a resin.
[10] A method for producing the fine cellulose fiber according to any one of the above aspects 1 to 6,
beating a cellulose raw material and then defibrating the cellulose raw material with a homomixer to obtain a fine cellulose fiber slurry; and optionally drying the fine cellulose fiber slurry under reduced pressure while stirring.
A method comprising:
[11] A method for producing the dried body according to aspect 7 or 8, comprising the steps of:
A cellulose raw material is beaten and then defibrated with a homomixer to obtain a fine cellulose fiber slurry;
drying the fine cellulose fiber slurry under reduced pressure while stirring; and optionally mixing the fine cellulose fiber slurry and/or the fine cellulose fibers with additional components.
A method comprising:
[12] A method for producing the resin composite according to aspect 9, comprising the steps of:
beating a cellulose raw material and then defibrating the cellulose raw material with a homomixer to obtain a fine cellulose fiber slurry; and optionally drying the fine cellulose fiber slurry under reduced pressure while stirring.
A process for producing fine cellulose fibers by a method comprising the steps of:
A mixing step of mixing the fine cellulose fibers and the resin;
A method comprising:
[13] The method according to any one of aspects 10 to 12, further comprising chemically modifying cellulose before, simultaneously with, and/or after the defibration.

According to one aspect of the present invention, fine cellulose fibers can be provided that are less likely to form agglomerates and have a good effect of improving the physical properties of resin composites.

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 calculating the average substitution degree of hydroxyl groups in cellulose.

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

<Fine cellulose fiber>
One aspect of the present invention provides fine cellulose fibers, in which the ratio of the settling height of the fine cellulose fibers to the total liquid height of the test dispersion (100%) when the test dispersion containing the fine cellulose fibers in water at a concentration of 0.05% by mass is left to stand at 23° C. and normal pressure for 24 hours is 6% or more. The fine cellulose fibers refer to cellulose defibrated by a method of mechanically finely pulverizing a cellulose raw material using a refiner, a high-pressure homogenizer, a ball mill, a homomixer, or the like. Fine cellulose fibers are usually very prone to aggregation and have strong interactions between the fibers, making it difficult to disperse them well in a resin. The present inventor unexpectedly discovered that fine cellulose fibers that exhibit a high settling height in a specific dilute aqueous dispersion of 0.05% by mass can maintain a suitable space between the fibers, making it difficult to form aggregates and can be dispersed well in a resin, while being able to impart an excellent physical property improvement effect to the resin due to the suitable entanglement between the fibers. Even when such fine cellulose fibers are used in a relatively small amount, they have an excellent effect of improving the physical properties of a composite containing fine cellulose fibers and a resin (also referred to as a resin composite in the present disclosure). The fine cellulose fibers of the present disclosure may be present in a dispersion (i.e., a slurry) or as a dried body. The fine cellulose fibers may be chemically modified as described below. Examples of the dispersion include dispersions containing, for example, 0.001 to 2 mass%, or 0.01 to 1.5 mass%, or 0.1 to 1 mass% of fine cellulose fibers, with the remainder being a dispersion medium. The dispersion medium may be, for example, water and/or an organic solvent. Examples of the organic solvent include water-miscible organic solvents, such as polyols (e.g., polyether polyols such as polypropylene glycol and polyethylene glycol), ethanol, methanol, dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone, acetic acid, and t-butanol.

The test dispersion is prepared by the following method. When the fine cellulose fibers are present in the form of a dispersion, the dispersion is converted into an aqueous dispersion with a fine cellulose fiber concentration of 0.05% by mass by solvent replacement and/or dilution or concentration to prepare the test dispersion. Concentration is performed by subjecting the dispersion to a filter cloth, membrane filter, centrifugation, etc. When the fine cellulose fibers are in a dry form, water is added and the fibers are redispersed using a homogenizer, etc. to prepare a test dispersion with a fine cellulose fiber concentration of 0.05% by mass.

In one embodiment, the ratio of the settling height is 6% or more, and preferably 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more. A high ratio of the settling height is an indicator that the fine cellulose fibers are well defibrated, and that the fibers maintain a moderate space between each other and are unlikely to form agglomerates, while also having a moderate amount of entanglement. On the other hand, if the ratio is too high (for example, when the fine cellulose fibers do not settle in the case of 100%), the fine cellulose fibers are likely to form an excessive network, making it difficult to disperse them in the resin, and as a result, agglomerates are likely to form, which may lead to a decrease in the physical properties of the resin composite. From this perspective, the upper limit of the ratio may be 80% or less, 70% or less, 60% or less, 50% or less, or 40% or less.

The sedimentation height ratio is measured by measuring the transmittance of the dispersion at a wavelength of 850 nm (hereinafter also referred to as initial transmittance) using, for example, a liquid dispersion stability evaluation device Turbiscan (manufactured by Sanyo Trading Co., Ltd.). After leaving the test tube at rest for 24 hours at 23° C., the height from the bottom of the dispersion to the separation interface and the height from the bottom of the dispersion to the top of the dispersion are measured using the liquid dispersion stability evaluation device, with the height at which the transmittance becomes 50% at the above wavelength being defined as the separation interface, and is calculated using the following formula (1):
Settling height ratio (%) = ([A] / [B]) × 100 ... (1)
(In formula (1), [A] is the height from the bottom surface of the dispersion to the separation interface, and [B] is the height from the bottom surface of the dispersion to the top surface of the dispersion.)
In addition, when the height at which the permeability becomes 50% is not defined, the region with a higher permeability than the initial permeability is defined as the supernatant portion, the region with a lower permeability than the initial permeability is defined as the sediment portion, and the boundary between the supernatant portion and the sediment portion is defined as the separation interface, and the sedimentation height ratio is calculated according to (1) above.

In one embodiment, the fine cellulose fiber of the present disclosure can be produced by a method including, for example, obtaining a fine cellulose fiber slurry by defibrating a cellulose raw material in dimethyl sulfoxide (also referred to as DMSO) using a homomixer, and optionally drying the fine cellulose fiber slurry under reduced pressure while stirring. When the cellulose raw material is dried under reduced pressure, the fine cellulose fiber of the present disclosure is obtained as a dry body. As a means for controlling the settling height, the above-mentioned cellulose raw material is subjected to a dry or wet grinding treatment, and in one embodiment, a cellulose raw material having a length-weighted average fiber length of 5 mm or less, preferably 4 mm or less, or 3 mm or less, or 2 mm or less, or 1 mm or less is produced, and the cellulose raw material is refined in a wet manner. If the cellulose raw material is 5 mm or less, uniform fine cellulose fibers are obtained in the subsequent refinement process, and aggregation in water is suppressed. Although the mechanism of this action is unclear, if the cellulose fibers are too long, it becomes difficult to apply shear energy, etc., uniformly during defibration. The non-uniform fine cellulose fibers obtained in this manner have a large fiber diameter due to the presence of thick fibers, and are prone to twisting and poorly dispersible in water. The lower limit of the length-weighted average fiber length of the cellulose raw material is preferably 0.1 mm or more, or 0.2 mm or more, or 0.3 mm or more, or 0.4 mm or more, or 0.5 mm or more to prevent a decrease in crystallinity due to excessive crushing treatment. The length-weighted average fiber length of the cellulose raw material can be measured, for example, by an optical measurement method (see JAPAN TAPPI Paper and Pulp Test Method No. 52 (Pulp and Paper - Fiber Length Test Method - Optical Automatic Measurement Method) or JIS P 8226 (Pulp - Fiber Length Measurement Method by Optical Automatic Analysis Method - Part 1: Polarized Method), JIS P 8226-2 (Pulp - Fiber Length Measurement Method by Optical Automatic Analysis Method - Part 2: Non-Polarized Method)).

As the cellulose raw material, 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.

Since the cellulose raw material contains alkali-soluble and sulfuric acid-insoluble components (such as lignin), the alkali-soluble and sulfuric acid-insoluble components may be reduced by a purification process such as delignification by cooking and a bleaching process. On the other hand, the purification process such as delignification by cooking and the bleaching process cut the molecular chains of cellulose, changing the weight-average molecular weight and number-average molecular weight, so it is important that the purification process and bleaching process of the cellulose raw material control the weight-average molecular weight of cellulose and the ratio of the weight-average molecular weight to the number-average molecular weight so that they 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 raw material, increasing the proportion of alkali-soluble matter present. Since alkali-soluble matter has poor heat resistance, it is important that the refining and bleaching processes of cellulose raw materials are controlled so that the amount of alkali-soluble matter contained in the cellulose raw material is kept below a certain value.

The cellulose raw material is obtained by a dry grinding process. Any type of grinder can be used in the dry grinding process, but a high-speed rotary impact grinder is preferable because it can produce cellulose raw material with a good shape. A high-speed rotary impact grinder is a grinder that uses pins that rotate in a grinding chamber or a rotor with a special structure to impact or shear the cellulose raw material and grind it. In addition, to suppress fiber damage during dry grinding, the cellulose raw material may contain moisture to a certain extent based on its weight.

Examples of mills with this type include the Jiyu mill, New Cosmomizer (manufactured by Nara Machinery Works, Ltd.), Victory Mill, Far In Victory Mill (manufactured by Hosokawa Micron, Ltd.), Turbo Mill (manufactured by Turbo Kogyo, Ltd.), Ultra Rotor (manufactured by W.I.R. Co., Ltd.), Makino type mill, Ultraplex (manufactured by Makino Sangyo, Ltd.), Fine Mill (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), Impeller Mill (manufactured by Seishin Enterprise Co., Ltd.), and Disc Refiner (manufactured by Aikawa Iron Works, Ltd.).

There is no particular restriction on the method of reducing the fiber diameter in order to convert the cellulose raw material into fine cellulose fibers, but it is preferable to make the defibration processing conditions (method of applying a shear field, size of the shear field, etc.) more efficient. In addition, in order to suppress the decrease in crystallinity due to shear, wet defibration using a solvent is preferable. There is no particular restriction on the defibration solvent, but examples include water and aprotic solvents. Water is preferable because it is an inexpensive solvent and does not require explosion-proofing of the production equipment. When the cellulose raw material is immersed in an aprotic solvent, cellulose swells in a short time, and the cellulose is finely pulverized by only applying slight stirring and shear energy. In addition, by adding a cellulose modifying agent before, during, or after fine pulverization, chemically modified fine cellulose fibers (also called chemically modified fine cellulose fibers) can be obtained directly without solvent replacement. Therefore, aprotic solvents are preferable from the viewpoint of production efficiency.

Examples of aprotic solvents include alkyl sulfoxides, alkyl amides, pyrrolidones, etc. These solvents can be used alone or in combination of two or more.

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

Examples of alkylamides include N,N-diC1-4 alkylformamides such as N,N-dimethylformamide (DMF) and N,N-diethylformamide; and N,N-diC1-4 alkylacetamides such as N,N-dimethylacetamide (DMAc) and N,N-diethylacetamide.

Examples of pyrrolidones include pyrrolidones such as 2-pyrrolidone and 3-pyrrolidone; N-C1-4 alkylpyrrolidone such as N-methyl-2-pyrrolidone (NMP); and the like.

These aprotic solvents can be used alone or in combination of two or more. Among these aprotic solvents, DMSO, DMF, DMAc, NMP, etc., especially DMSO, can be used to more efficiently produce chemically modified fine cellulose fibers. The mechanism of action is not entirely clear, but it is presumed to be due to uniform micro-swelling of the cellulose raw material in the aprotic solvent. In addition, since the swelling state of the cellulose raw material differs between water and aprotic solvents, which are generally used in the production of fine cellulose fibers, as described above, the fiber diameter and shape of the obtained fine cellulose fibers may differ. The fiber diameter and shape are related to the dispersion state and network formation in water or resin, and are also thought to affect the sedimentation height ratio.

The cellulose raw material can be refined using a device that effectively applies shear to the cellulose raw material, such as a disintegrator, beater, refiner, low-pressure homogenizer, high-pressure homogenizer, ultra-high-pressure homogenizer, emulsifier, homomixer, grinder, mass colloider, cutter mill, ball mill, bead mill, jet mill, single-screw extruder, twin-screw extruder, ultrasonic agitator, or household juicer mixer. Among these, the homomixer using an aprotic solvent is preferred because it can defibrate the cellulose raw material with low energy and allows chemical modification of the fine cellulose fibers in a non-aqueous system.

The procedure for pulverization in the homomixer includes, but is not limited to, the following. In one embodiment, the homomixer includes a first means for supplying the contents, a second means having a rotating element capable of generating a shear force and a protruding pressure on the contents from the first means, and optionally a third means capable of returning the contents from the second means to the first means. In one embodiment, the second means is disposed below the first means, the contents are fed to the second means by the first means, and are returned to the first means via the third means by the discharge pressure of the second means, thereby enabling extremely efficient defibration of cellulose by shear force. The first means may be an agitator such as a stirring propeller, and the agitator may have a scraper capable of scraping off the contents along the inner wall surface of the tank. The second means may be an ultra-high speed homogenizer (rotor/stator type) attached to the bottom of the tank. The second means can crush and disperse the contents to a sub-micron level by energy such as shear force and collision between solids. The third means may be a recirculation pipe that sends the contents from the second means (e.g., the discharge from the homogenizer) to the top or middle of the tank and returns it to the first means.

In one embodiment, in the case of a homomixer with a tank capacity of 35 L or more, extremely low energy of 0.5 to 80 kWh of rated power consumption per kg of cellulose dry solids can be imparted to the cellulose raw material. Such low-energy defibration is preferable in that the settling height of the fine cellulose fibers can be easily controlled. In one embodiment, low-energy defibration using shear force by rotating the rotating element of the second means at a peripheral speed of 20 m/s to 80 m/s and preferably at 20°C to 90°C for 0.5 hours to 8 hours is preferable in that the settling height of the fine cellulose fibers can be easily controlled.

In one aspect, the number average fiber diameter of the microfine cellulose fibers is preferably 2 to 1000 nm from the viewpoint of obtaining a good effect of improving physical properties by the microfine cellulose fibers. The number average fiber diameter of the microfine 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 fine 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 fine cellulose fibers with a small amount of the fine cellulose fibers. The upper limit is not particularly limited, but is preferably 5,000 or less from the viewpoint of handleability.

In the present disclosure, the length, diameter, and L/D ratio of each of the fine cellulose fibers are determined by diluting an aqueous dispersion of the fine cellulose fibers with a water-soluble solvent (e.g., water, ethanol, tert-butanol, etc.) to 0.01 to 0.1% by mass, dispersing the fibers using a high-shear homogenizer (e.g., IKA, product name "Ultra Turrax T18") under processing conditions: rotation speed of 25,000 rpm for 5 minutes, casting the fibers on mica, and air-drying the fibers to obtain a measurement sample, which is then measured using a high-resolution scanning electron microscope (SEM) or atomic force microscope (AFM). Specifically, the length (L) and diameter (D) of 100 randomly selected fibrous substances are measured in an observation field where the magnification is adjusted so that at least 100 fibrous substances are observed, and the ratio (L/D) is calculated. 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) of the fine cellulose fibers are calculated.

The length, diameter, and L/D ratio of the fine cellulose fibers in the resin composite described below can be confirmed by measuring the solid resin composite as a measurement sample using the above-mentioned measurement method. Alternatively, the length, diameter, and L/D ratio of the fine cellulose fibers in the resin composite can be confirmed by dissolving the resin components in the resin composite in an organic or inorganic solvent that can dissolve the resin components of the resin composite, separating the fine cellulose fibers, thoroughly washing with the solvent, and then replacing with a water-soluble solvent (e.g., water, ethanol, tert-butanol, etc.), preparing a 0.01 to 0.1 mass% dispersion, and redispersing with a high-shear homogenizer (e.g., IKA, product name "Ultra Turrax T18"). The redispersion can be confirmed by casting the redispersion on mica, air-drying it, and measuring it as a measurement sample using the above-mentioned measurement method. At this time, the measurement is performed on 100 or more randomly selected fine cellulose fibers.

The crystallinity of the fine 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 fine 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 fine 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 set the crystallinity of the fine cellulose fibers within the above-mentioned range.

When the fine cellulose fibers are cellulose type I crystals (derived from natural cellulose), the degree of crystallinity can be calculated from the diffraction pattern (2θ/deg. is 10 to 30) obtained by measuring a sample by wide-angle X-ray diffraction using the Segal method, as shown in 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 fine cellulose fibers are cellulose II type crystals (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 the cellulose II type crystals 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 fine cellulose fibers disclosed herein have relatively high structural mobility, and by dispersing the fine cellulose fibers in a resin, a resin composite having a lower linear expansion coefficient and superior strength and elongation during tensile and bending deformation can be obtained. Therefore, cellulose fibers containing cellulose type I crystals or cellulose type II crystals are preferred, and fine cellulose fibers containing cellulose type I crystals and having a crystallinity of 55% or more are more preferred.

The degree of polymerization of the fine 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, 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 fine cellulose fiber 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 fine 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 "15th Revised Japanese Pharmacopoeia Commentary (published by Hirokawa Shoten)."

In one embodiment, the weight average molecular weight (Mw) of the fine cellulose fiber is 100,000 or more, more preferably 200,000 or more, and even more preferably 250,000 or more. The ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight (Mn) is 10 or less, or 9 or less, or 8 or less, or 7 or less, or 6 or less, and 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, particularly when the weight average molecular weight of the cellulose molecules of the fine cellulose fibers is large and the weight average molecular weight is large and the width of the molecular weight distribution is narrow, a particularly high heat resistant fine cellulose fiber and a resin composite containing the fine cellulose fibers and the resin can be obtained. The weight average molecular weight (Mw) of the fine cellulose fiber may be, for example, 1,000,000 or less, or 900,000 or less, or 800,000 or less, or 700,000 or less, or 600,000 or less, or 500,000 or less, from the viewpoint of the availability of the cellulose raw material. The ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight (Mn) may be, for example, 1.5 or more, or 2 or more, from the viewpoint of the ease of production of the fine cellulose fiber. Mw can be controlled to the above range by selecting a cellulose raw material having an Mw according to the purpose, appropriately performing physical treatment and/or chemical treatment on the cellulose raw material in an appropriate range, etc. Mw/Mn can also be controlled to the above range by selecting a cellulose raw material having an Mw/Mn according to the purpose, appropriately performing physical treatment and/or chemical treatment on the cellulose raw material in an appropriate range, etc. In both the control of Mw and the control of Mw/Mn, examples of the physical treatment include dry or wet grinding using a microfluidizer, ball mill, or disk mill, or physical treatment that applies mechanical forces such as impact, shear, shear, or friction using a crusher, homomixer, high-pressure homogenizer, or ultrasonic device, and examples of the chemical treatment include digestion, bleaching, acid treatment, and conversion to regenerated cellulose.

The weight average molecular weight and number average molecular weight of cellulose referred to here are values obtained by dissolving cellulose in N,N-dimethylacetamide containing added 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 fine cellulose fibers include hydrolysis. Hydrolysis promotes depolymerization of the amorphous cellulose inside the fine cellulose fibers, decreasing the average degree of polymerization. At the same time, hydrolysis removes impurities such as hemicellulose and lignin in addition to the above-mentioned amorphous cellulose, 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, microwave decomposition, and the like. 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 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 cellulose is treated for 10 minutes or more at 100°C or higher under pressure using an aqueous mineral acid solution of 2% by mass or less. Under these conditions, the catalyst components such as acid penetrate into the inside of the fine cellulose fibers, promoting hydrolysis, reducing the amount of catalyst components used, and making subsequent purification easier. In addition, the dispersion of the cellulose 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.

The alkali-soluble polysaccharides that may be contained in the fine cellulose fibers include hemicellulose, as well as β-cellulose and γ-cellulose. Those skilled in the art will understand alkali-soluble polysaccharides as the components obtained as the alkali-soluble portion of holocellulose obtained by solvent extraction and chlorine treatment of plants (e.g., wood) (i.e., the components obtained by removing α-cellulose from holocellulose). Alkali-soluble polysaccharides are polysaccharides that contain hydroxyl groups and have poor heat resistance, and may decompose when exposed to heat, cause yellowing during thermal aging, and cause a decrease in the strength of the cellulose fibers. Therefore, it is preferable that the content of alkali-soluble polysaccharides in the fine cellulose fibers is low.

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

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 fine cellulose fiber is preferably 10% by mass or less, 5% by mass or less, or 3% by mass or less, based on 100% by mass of the fine cellulose fiber, from the viewpoint of avoiding a decrease in the heat resistance of the fine cellulose fiber and the associated discoloration. From the viewpoint of ease of production of the fine cellulose fiber, the above content may be 0.01% by mass or more, 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 this acid-insoluble component, and the number average of the acid-insoluble component contents calculated for the three samples is taken as the average acid-insoluble component content.

The fine cellulose fibers may be chemically treated (e.g., oxidized or chemically modified using a modifying agent). As an example, fine cellulose fibers obtained by oxidizing cellulose fibers with 2,2,6,6-tetramethylpiperidine-1-oxyl radical as shown in Cellulose (1998) 5, 153-164, followed by washing and mechanical fiberization, may be used.

As a cellulose modification agent, 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=CH ₂ ...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.

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.

The degree of modification of the chemically modified fine cellulose fiber of this embodiment is expressed as the average degree of substitution of hydroxyl groups (the average number of hydroxyl groups substituted per glucose, which is the basic structural unit of cellulose, also referred to as DS). In one aspect, the DS of the chemically modified fine cellulose fiber is preferably 0.01 or more and 2.0 or less. If the DS is 0.01 or more, a resin composite containing chemically modified fine cellulose with a high thermal decomposition onset temperature can be obtained. On the other hand, if the DS is 2.0 or less, an unmodified cellulose skeleton remains in the chemically modified fine cellulose, so that a resin composite containing chemically modified fine cellulose that combines high tensile strength and dimensional stability derived from cellulose and a high thermal decomposition onset temperature derived from chemical modification can be obtained. The DS is more preferably 0.05 or more, even more preferably 0.1 or more, particularly preferably 0.2 or more, and most preferably 0.3 or more, and more preferably 1.8 or less, even more preferably 1.5 or less, particularly preferably 1.2 or less, and most preferably 1.0 or less.

When the modifying group of the chemically modified fine cellulose fiber is an acyl group, the degree of acyl substitution (DS) can be calculated based on the peak intensity ratio of the peak derived from the acyl group to the peak derived from the cellulose skeleton from the reflection type infrared absorption spectrum of the esterified fine cellulose fiber. The peak of the absorption band of C=O based on the acyl group appears at 1730 cm ^-1 , and the peak of the absorption band of C-O based on the cellulose skeleton appears at 1030 cm ^-1 (see Figures 1 and 2). The DS of the esterified fine cellulose fiber is obtained by preparing a correlation graph between the DS obtained from the solid-state NMR measurement of the esterified fine cellulose fiber described later and the modification rate (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 the cellulose skeleton C-O, 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 fine cellulose fiber by solid-state NMR can be calculated by carrying out ^13C solid-state NMR measurement on the frozen and pulverized esterified fine cellulose fiber, and calculating the DS from the total area intensity (Inp) of the signals assigned to carbons C1-C6 derived from the pyranose ring of cellulose appearing in the range of 50 ppm to 110 ppm relative to the area intensity (Inf) of the signal assigned to one carbon atom derived from the modifying group, using the following formula:
DS=(Inf)×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 Avance500WB
Frequency: 125.77MHz
Measurement method: DD/MAS method Waiting time: 75 sec
NMR sample tube: 4 mm diameter
Accumulation times: 640 times (approximately 14 hours)
MAS: 14,500Hz
Chemical shift reference: glycine (external reference: 176.03 ppm)

<Dry product>
One aspect of the present invention provides a dried body (also referred to as a fine cellulose fiber dried body or dried body) containing the fine cellulose fibers of the present disclosure. The dried body may be composed of only fine cellulose fibers, or may contain fine cellulose fibers and additional components. Examples of the additional components include dispersants, fine fiber filler components made of highly heat-resistant organic or inorganic polymers such as aromatic aramids, compatibilizers, plasticizers, polysaccharides, natural proteins, inorganic compounds, colorants, fragrances, pigments, flow control agents, leveling agents, conductive agents, antistatic agents, UV absorbers, UV dispersants, deodorants, and preservatives. The dried body can be produced, for example, by obtaining a fine cellulose fiber slurry by the above-mentioned method for producing fine cellulose fibers, and then heating and drying the slurry under stirring or drying under reduced pressure. The dried body containing fine cellulose fibers and additional components can be produced by a method of adding additional components to a fine cellulose fiber slurry, and then heating and drying the slurry under stirring or drying under reduced pressure, or by a method of mixing a dried body of fine cellulose fibers with additional components.

<Dispersant>
The dispersant means a compound that has the function of stably dispersing fine cellulose fibers and improves or controls the dispersion state of the fine cellulose fibers in the resin, thereby improving the mechanical properties of the resin composite produced using the fine cellulose fibers. In a preferred embodiment, the fine cellulose fibers are dispersed in the resin composite in the form of a dispersion containing a dispersant and fine cellulose fibers dispersed in the dispersant. That is, the resin composite is preferably a dispersion in which fine cellulose fibers are dispersed in a dispersant, and the dispersion is dispersed in the resin. The mass ratio of the fine cellulose fibers to the total of 100 mass% of the fine cellulose fibers and the dispersant is preferably 10 mass% or more, or 20 mass% or more, or 30 mass% or more, and preferably 99 mass% or less, or 95 mass% or less, or 90 mass% or less. The dispersant can be at least one selected from the group consisting of surfactants, organic compounds having a boiling point of 160 ° C. or more, and resins having a chemical structure capable of highly dispersing fine cellulose fibers, and is preferably at least one selected from the group consisting of surfactants and organic compounds having a boiling point of 160 ° C. or more.

As the surfactant, any of anionic surfactants, nonionic surfactants, amphoteric surfactants, and cationic surfactants can be used, but in terms of affinity with fine cellulose fibers, anionic surfactants and nonionic surfactants are preferred, and nonionic surfactants are more preferred.

As the hydrophilic group of the surfactant, polyoxyethylene chain, carboxyl group, and hydroxyl group are preferred in terms of affinity with fine cellulose fibers, and polyoxyethylene chain is particularly preferred. Nonionic polyoxyethylene derivatives are particularly preferred. The polyoxyethylene chain length of the polyoxyethylene derivative may be 3 or more, or 5 or more, or 10 or more, or 15 or more. The longer the chain length, the higher the affinity with fine cellulose fibers, but from the viewpoint of balance with the desired properties of the resin composite (e.g., mechanical properties), the polyoxyethylene chain length may be 60 or less, or 50 or less, or 40 or less, or 30 or less, or 20 or less.

As the structure of the hydrophobic group of the surfactant, alkyl ether type, alkyl phenyl ether type, rosin ester type, bisphenol A type, β-naphthyl type, styrenated phenyl type, and hardened castor oil type are preferred in terms of high affinity with resin. The number of carbon atoms in the alkyl chain of the hydrophobic group (the number of carbon atoms excluding the phenyl group in the case of alkyl phenyl) is preferably 5 or more, or 10 or more, or 12 or more, or 16 or more. For example, when the resin is a polyolefin resin, the greater the carbon number of the surfactant, the higher the affinity with the resin. The carbon number may be, for example, 30 or less, or 25 or less.

As the hydrophobic group, those having a cyclic structure or those having a bulky and multifunctional structure are more preferable. As hydrophobic groups having a cyclic structure, alkylphenyl ether type, rosin ester type, bisphenol A type, β-naphthyl type, and styrenated phenyl type groups are preferable, and as those having a multifunctional structure, hydrogenated castor oil type (e.g. hydrogenated castor oil ether) groups are preferable. Rosin ester type and hydrogenated castor oil type are particularly preferable.

In a preferred embodiment, the surfactant is a polyethylene glycol (PEG)-polypropylene glycol (PPG) copolymer.

In one embodiment, the moisture content of the dry material containing fine cellulose fibers can be controlled to preferably 50% by mass or less, more preferably 0.01 to 40% by mass, even more preferably 0.1 to 30% by mass, particularly preferably 0.1 to 20% by mass, and most preferably 0.1 to 10% by mass, based on the total amount of the dry material.

In one embodiment, the bulk density of the dry material containing fine cellulose fibers is preferably 0.05 g/ml to 1 g/ml, or 0.1 g/ml to 0.8 g/ml, or 0.2 g/ml to 0.7 g/ml, or 0.3 g/ml to 0.6 g/ml, in order to keep storage and transportation costs low while maintaining good dispersion of the fine cellulose fibers in the resin complex. The bulk density is measured using a powder tester (PT-N type, manufactured by Hosokawa Micron Corporation), and the value of Pack Density is measured as the bulk density.

In one embodiment, the settling height ratio of the slurry when the dried fine cellulose fiber body having a fine cellulose fiber concentration of 0.05% by mass is redispersed in water is preferably 5% to 50%, or 5% to 40%, or 5% to 30%, or 5% to 20%, or 10% to 20% in order to achieve good dispersion of the fine cellulose fiber in the resin composite. The settling height ratio is a value measured after preparing a dispersion as described below. Distilled water is added to the dried fine cellulose fiber body so that the fine cellulose fiber is 0.05% by mass to prepare 20 g of a test dispersion. 20 g of the test dispersion is dispensed into a 30 ml glass vial, dispersed with a homogenizer (rotation speed 10,000 rpm, 5 minutes), placed in a screw-cap test tube (inner diameter 12 mm), sealed, and manually shaken to obtain a uniform dispersion.

<Resin composite>
One aspect of the present invention provides a resin composite comprising the fine cellulose fibers of the present disclosure and a resin. In one aspect, the fine cellulose fibers are well dispersed in the resin with an appropriate space between them, so that they are unlikely to form aggregates, while the moderate entanglement between the fibers provides an excellent property-improving effect on the resin, so that even if a small amount of fine cellulose fibers is used, the resin composite can have excellent properties.

<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-based 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-based resins include ethylene-based (co)polymers such as low-density polyethylene (e.g., linear low-density polyethylene), high-density polyethylene, ultra-low-density polyethylene, and ultra-high-molecular-weight polyethylene; polypropylene-based (co)polymers such as polypropylene, ethylene-propylene copolymer, and ethylene-propylene-diene copolymer; and copolymers of ethylene and α-olefins such as ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer, and ethylene-glycidyl methacrylate copolymer.

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 upper limit from the viewpoint of improving the toughness of the resin composite, and it is desirable that the MFR does not exceed the lower limit from the viewpoint of the fluidity of the resin composite.

In addition, in order to increase the affinity with fine 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, and 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 polyolefin resins mentioned above can be used, but polypropylene is particularly suitable. The acid-modified polypropylene resin may be used alone, but it is more preferable to use it in combination with an unmodified polypropylene resin in order to adjust the modification rate of the resin as a whole. In this case, the ratio of the acid-modified polypropylene resin to all polypropylene resins is preferably 0.5% by mass to 50% by mass. A more preferred lower limit is 1% by mass, or 2% by mass, or 3% by mass, or 4% by mass, or 5% by mass. A more preferred upper limit is 45% by mass, or 40% by mass, or 35% by mass, or 30% by mass, or 20% by mass. In order to maintain the interfacial strength between the resin and the fine cellulose fibers, a content equal to or greater than the lower limit is preferred, and in order to maintain the ductility of the resin, a content equal to or less than the upper limit is preferred.

The melt mass flow rate (MFR) of the acid-modified polypropylene resin, measured in accordance with ISO1133 at 230°C and a load of 21.2 N, is preferably 50 g/10 min or more, 100 g/10 min or more, 150 g/10 min or more, or 200 g/10 min or more, from the viewpoint of increasing the affinity at the interface between the resin and the fine 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 fine 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.

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 compound, monoamine compound, dicarboxylic acid compound, monocarboxylic acid compound, acid anhydride, monoisocyanate, monoacid halide, monoester, monoalcohol, 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 above. Among these, in terms of reactivity, stability of the blocked terminal, and price, one or more 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 are preferred, and acetic acid is most preferred.

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 0.45 from the viewpoint of dispersibility of the fine 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 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 alkyl type epoxy resin; epoxy resins modified with cyclohexylmaleimide and glycidyl methacrylate; epoxy resins modified with cyclohexylmaleimide and glycidyl methacrylate; epoxy-modified polybutadiene rubber derivatives; CTBN-modified epoxy resins; trimethylolpropane polyglycidyl ether; Phenyl-1,3-diglycidyl ether, biphenyl-4,4'-diglycidyl ether, 1,6-hexanediol diglycidyl ether, 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 and vinyl compounds (e.g., certain vinyl ethers). Examples of cationic reaction types include epoxy compounds and certain vinyl ethers. For example, epoxy compounds that can be used as cationic reaction types can be monomers for both thermosetting 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 methylstyrene and ethylstyrene. 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.

The amount of fine cellulose fibers per 100 parts by mass of resin (in one embodiment, thermoplastic resin) is preferably within the range of 0.001 to 100 parts by mass. The lower limit of the amount of fine cellulose fibers is more preferably 0.01 parts by mass, even more preferably 0.1 parts by mass, and most preferably 1 part by mass. The upper limit of the amount of fine cellulose fibers is more preferably 80 parts by mass, even more preferably 70 parts by mass, and most preferably 50 parts by mass. From the viewpoint of the balance between processability and mechanical properties, it is desirable to set the amount of fine cellulose fibers within the above-mentioned range.

<Method for producing resin composite>
In one embodiment, the resin composite can be produced by a method including a fine cellulose fiber production step of obtaining fine cellulose fibers by a method including beating a cellulose raw material and then defibrating it with a homomixer to obtain a fine cellulose fiber slurry, and optionally drying the fine cellulose fiber slurry under reduced pressure while stirring, and a mixing step of mixing the fine cellulose fibers (i.e., the fine cellulose fiber slurry or dried body) with a resin. More specifically, the resin composite can be produced by, for example, the following method depending on the type of resin. When producing a resin composite containing chemically modified fine cellulose fibers, the order of chemical modification and defibration does not matter, and cellulose may be chemically modified before defibration, simultaneously with defibration, and/or after defibration.

When the resin is a thermoplastic resin, the fine cellulose fibers of the present disclosure can be kneaded with the thermoplastic resin in the form of a dispersion or a dried body (which may further contain additional components) to produce a resin composite.
- A method in which a resin monomer and fine cellulose fibers are mixed, a polymerization reaction is carried out, the resulting resin composition 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 fine 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 a resin and fine cellulose fibers is melt-kneaded using a single-screw or twin-screw extruder, extruded into a rod-like or tubular shape, and cooled to obtain an extrusion molded product;
A method in which a mixture of resin and fine 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 fine 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 fine cellulose fibers is a method in which a resin and fine cellulose fibers transported in a desired ratio are mixed and then melt-kneaded.

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 fine cellulose fibers and the 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, and cylindrical shapes, which vary 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 fine cellulose fibers in a resin solution or resin powder dispersion and drying the resulting mixture, a method of thoroughly dispersing fine cellulose fibers in a resin monomer liquid and polymerizing the resulting mixture by heat, UV irradiation, a polymerization initiator, or the like, a method of thoroughly impregnating a molded body (e.g., a sheet, a powder particle molded body, etc.) made of fine cellulose fibers with a resin solution or resin powder dispersion and drying the resulting mixture, or a method of thoroughly impregnating a molded body made of fine cellulose fibers with a resin monomer liquid and polymerizing the resulting mixture by heat, UV irradiation, a polymerization initiator, or the like. When curing, various polymerization initiators, curing agents, curing accelerators, polymerization inhibitors, etc. can be blended.

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. Examples of the method of 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, various curing methods using active energy rays can be used to produce a resin molded body.

When the resin is an elastomer, a resin composite can be produced by a method of dry kneading fine cellulose fibers and raw rubber, or a method of dispersing or dissolving fine 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-type stirring device, a rotary stirring device, an electromagnetic stirring device, 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 a 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 molded product.

A resin molded product containing a thermoplastic resin or an 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 molded product 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 molded products may be subjected to secondary processing such as annealing, etching, corona treatment, plasma treatment, embossing, cutting, and surface polishing.

In the resin composite, the amount of fine 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.

The resin composite of this embodiment is highly heat resistant and lightweight, and can therefore be used as a substitute for steel plates, fiber-reinforced plastics such as carbon fiber reinforced plastics and glass fiber reinforced plastics, and resin composites containing inorganic fillers. For example, industrial machine parts (e.g., electromagnetic device housings, roll materials, transport arms, medical device parts, etc.), general machine parts, automobile, railway, and vehicle parts (e.g., outer panels, chassis, aerodynamic parts, seats, friction materials inside transmissions, etc.), ship parts (e.g., hulls, seats, etc.), aviation-related parts (e.g., fuselages, main wings, tails, movable surfaces, fairings, cowls, doors, seats, interior materials, etc.), spacecraft and artificial satellite parts (motor cases, main wings, structures, antennas, etc.), electronic and electrical parts (e.g., personal computer housings, mobile phone housings, office automation equipment, audio-visual equipment, telephones, facsimiles, home appliances, toys, etc.), construction and civil engineering materials (e.g., rebar replacement materials, truss structures, cables for suspension bridges, etc.), daily necessities, sports and leisure goods (e.g., golf club shafts, fishing rods, tennis or badminton rackets, etc.), wind power generation housing parts, etc., and container and packaging parts.

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

<Production of fine cellulose fibers>
[Production Example 1]
The cotton linter pulp was treated with a hammer mill (HM-500, manufactured by LabNect, screen mesh φ0.7 mm) to obtain pulverized pulp P1.

[Production Example 2]
A pulverized pulp P2 was obtained in the same manner as in Production Example 1, except that the screen mesh was changed to φ0.3 mm.

[Production Example 3]
Ground pulp P3 was obtained by the method of Production Example 2, except that the cotton linter pulp was replaced with abaca pulp.

[Production Example 4]
Ground pulp P4 was obtained in the same manner as in Production Example 1, except that the cotton linter pulp was replaced with NBKP.

[Example 1: Defibration only, pulverized pulp P1]
A KAPPA VITA (registered trademark) homomixer (tank size 35 L) was charged with 1 part by mass of ground pulp P1 and 19 parts by mass of DMSO, and the mixture was treated for 8 hours at a homomixer rotation speed of 6000 rpm (circumferential speed 29 m/s) to obtain a fine cellulose fiber slurry (slurry S1, DMSO solvent). After concentrating the slurry S1 with a dehydrator, 30 parts by mass of pure water was added, thoroughly stirred, and the mixture was concentrated again in the dehydrator. After this, a series of washing operations, including the addition of 30 parts by mass of pure water, stirring, and concentration, was repeated a total of five times to remove DMSO, and 10 parts by mass of a fine cellulose fiber cake (cake K1, water solvent) with a solid content of 10% by mass was obtained.

[Example 2: Sequential method (acetylation after defibration), pulverized pulp P1]
To the fine cellulose fiber slurry (slurry S2, DMSO solvent) obtained in the same manner as in Example 1, 2.1 parts by mass of vinyl acetate and 0.32 parts by mass of sodium bicarbonate were added, and acetylation was carried out at 60 ° C. for 4 hours to obtain a fine cellulose fiber slurry (slurry S3, DMSO solvent). In order to prevent retention in the circulation line, the treatment was carried out at a homomixer rotation speed of 2000 rpm (circumferential speed 12 m / s). The acetylation reaction was stopped by adding 30 parts by mass of pure water to the slurry S3 and thoroughly stirring it, and the slurry was placed in a dehydrator and concentrated. After this, the same washing operation as in Example 1 was repeated five times to remove DMSO, vinyl acetate, sodium bicarbonate, and by-products, and 10 parts by mass of acetylated fine cellulose fiber cake (cake K2, water solvent) with a solid content of 10% by mass was obtained.

[Example 3: Simultaneous method (simultaneous defibration and acetylation), pulverized pulp P2]
To a KAPPA VITA (registered trademark) homomixer (tank size 35 L), 1 part by mass of ground pulp P2, 19 parts by mass of DMSO, 2.1 parts by mass of vinyl acetate, and 0.32 parts by mass of sodium bicarbonate were added, and defibration and acetylation were simultaneously performed for 4 hours at a homomixer rotation speed of 6000 rpm (circumferential speed 29 m/s) and a treatment temperature of 60° C. to obtain a fine cellulose fiber slurry (slurry S4, DMSO solvent). The subsequent reaction termination by addition of water and washing operations were performed in the same manner as in Example 2, and 10 parts by mass of an acetylated fine cellulose fiber cake (cake K3, water solvent) with a solid content of 10% by mass was obtained.

[Example 4: Sequential process, ground pulp P3]
A fine cellulose fiber cake (cake K4, water solvent) having a solid content of 10% by mass was obtained in 10 parts by mass in the same manner as in Example 2, except that ground pulp P3 was used instead of ground pulp P1.

[Example 5: Defibration only, pulverized pulp P1]
The same method as in Example 1 was used to obtain 10 parts by mass of a fine cellulose fiber cake (Cake K5, water solvent) having a solid content of 10% by mass, except that the homomixer treatment time was changed to 24 hours.

[Comparative Example 1: Simultaneous method, cotton linter pulp]
10 parts by mass of an acetylated fine cellulose fiber cake (cake K6, water solvent) having a solid content of 10% by mass was obtained in the same manner as in Example 3, except that cotton linter pulp was used instead of ground pulp P1.

[Comparative Example 2: Sequential process, abaca pulp]
A fine cellulose fiber cake (cake K7, water solvent) having a solid content of 10% by mass was obtained in 10 parts by mass in the same manner as in Example 2, except that abaca pulp was used instead of ground pulp P1.

[Comparative Example 3: Defibration only (water solvent), pulverized pulp P4]
One part by mass of the ground pulp P4 was stirred at room temperature for 1 hour at 500 rpm in 50 parts by mass of water using a single-shaft agitator (DKV-1 φ125 mm dissolver manufactured by IMEX). The mixture was then fed to a bead mill (NVM-1.5 manufactured by IMEX) using a hose pump, and circulated for 180 minutes using only water to obtain 51 parts by mass of a fine cellulose fiber slurry (slurry S5, water solvent) having a solid content of 2.0% by mass. Finally, the slurry S5 was concentrated in a dehydrator to obtain 10 parts by mass of a fine cellulose fiber cake (K8, water solvent) having a solid content of 10% by mass.
During the 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 the circulation operation, the slurry temperature was controlled at 40° C. using a chiller to absorb heat generated by friction.

[Comparative Example 4: Defibration only (DMSO solvent), pulverized pulp P4]
31 parts by mass of a fine cellulose fiber slurry (Slurry S6, DMSO solvent) having a solid content of 3.2% by mass was obtained in the same manner as in Comparative Example 3, except that 30 parts by mass of DMSO was used instead of 50 parts by mass of water. 30 parts by mass of pure water was added to the slurry S6, which was thoroughly stirred and then placed in a dehydrator for concentration. The obtained wet cake was dispersed again in 30 parts by mass of pure water, stirred, and concentrated. The washing operation was repeated a total of five times to remove DMSO, and 10 parts by mass of a fine cellulose fiber cake (K9, water solvent) having a solid content of 10% by mass was obtained.
The physical properties of the cellulose raw material, pulverized pulp, and fine cellulose fibers are shown in Table 1.

The settling height ratio of fine cellulose fibers using pulverized pulp was higher than that of fibers using unpulverized cellulose raw materials. When the solvent used during defibration was water, the number average fiber diameter was smaller than that of DMSO, and the settling height ratio was higher. Although the length-weighted average fiber length of the pulverized pulp of wood pulp-based NBKP was small, the settling height ratio was small.

<Method for producing dried fine cellulose fiber body>
To the fine cellulose fiber cakes K1 to K9 obtained in Examples 1 to 5 and Comparative Examples 1 to 4, 3% by mass of hydrogenated castor oil ether (RCW-20, manufactured by Aoki Oil & Fat) was added, and the mixture was stirred in a planetary mixer (Primix Corporation, product name "Hibismix 2P-1") at 50 rpm for 10 minutes at 25°C and atmospheric pressure, and then dried under reduced pressure at 50 rpm for 8 hours at a jacket temperature of 80°C and reduced pressure of -0.1 MPa to obtain dried fine cellulose fibers (CNF1 to 9). In the dried fine cellulose fiber, the mass ratio of fine cellulose fiber/hydrogenated castor oil ether was 10/3.
The physical properties of the dried fine cellulose fiber material and the resin composite are shown in Table 2.
When the settling height ratio of the fine cellulose fiber itself was high, the settling height ratio of the dried fine cellulose fiber also showed a high value. This is thought to be because the fine cellulose fiber was well defibrated and an advanced network was formed in water. In addition, various physical properties of the resin composite were also excellent.

<Evaluation of cellulose raw materials and crushed pulp>
[Length-weighted average fiber length]
The fiber length was measured using a fiber length measuring device (Kajaani FiberLab V4 (manufactured by Metso Automation)) in accordance with JIS P 8226-2 "Pulp - Fiber length measurement method by optical automatic analysis method, Part 2: Non-polarized light method."

<Evaluation of fine cellulose fibers>
The physical properties of the fine cellulose fibers were evaluated using a porous sheet prepared by the following method.
[Porous sheet]
First, the wet cake was added to tert-butanol, and further dispersed in a mixer or the like until no aggregates were present. The concentration was adjusted to 0.5% by mass per 0.5 g of fine cellulose fiber solid content. 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 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

[Average fiber diameter]
The wet cake was diluted to 0.01% by mass with tert-butanol, 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 microscope. The measurement was performed by adjusting the magnification so that at least 100 cellulose fibers were observed, and the minor diameter (D) of 100 randomly selected cellulose fibers was measured, and the arithmetic average of the 100 cellulose fibers was calculated.

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

[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 it was dissolved by visual observation. The solution in which cellulose was dissolved was filtered through a 0.45 μm filter, and the filtrate was used as a sample for gel permeation chromatography. The apparatus and measurement conditions used are as follows.
Equipment: Tosoh Corporation HLC-8120
Column: TSKgel SuperAWM-H (6.0 mm ID x 15 cm) x 2 Detector: RI detector Eluent: N,N-dimethylacetamide (lithium chloride 0.2%)
Flow rate: 0.6 mL/min. Calibration curve: Pullulan equivalent

[Average content of 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 fine 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 fine cellulose fibers.

[Settling height ratio]
A test dispersion was prepared by adding distilled water to the fine cellulose fiber cake so that the fine cellulose fiber was 0.05% by mass. 20 ml of the test dispersion was dispensed into a 30 ml glass vial, and then dispersed with a homogenizer (10,000 rpm, 1 minute). Then, 8 ml of the test dispersion was quickly placed in a screw-top test tube (12 mm inner diameter), sealed, and manually shaken to make the dispersion uniform. The transmittance (hereinafter also referred to as initial transmittance) of the dispersion at a wavelength of 850 nm was measured using a liquid dispersion stability evaluation device Turbiscan (manufactured by Sanyo Trading Co., Ltd.). In addition, after leaving this test tube at 23 ° C. for 24 hours, the height from the bottom of the dispersion to the separation interface and the height from the bottom of the dispersion to the top of the dispersion were measured using the liquid dispersion stability evaluation device, with the height at which the transmittance becomes 50% at the above wavelength being defined as the separation interface, and the following formula (1):
Settling height ratio (%) = ([A] / [B]) × 100 ... (1)
(In formula (1), [A] is the height from the bottom surface of the dispersion to the separation interface, and [B] is the height from the bottom surface of the dispersion to the top surface of the dispersion.)
In addition, when the height at which the permeability becomes 50% was not defined, the region with a higher permeability than the initial permeability was defined as the supernatant portion, and the region with a lower permeability than the initial permeability was defined as the sediment portion, and the boundary between the supernatant portion and the sediment portion was defined as the separation interface, and the sedimentation height ratio was determined according to (1) above.
The larger the sedimentation height ratio, the better the dispersibility in the resin composite, the easier it is to form a network of fine cellulose fibers, and the better the mechanical properties (particularly tensile elongation and tensile strength).

<Evaluation of dried fine cellulose fiber>
[Settling height ratio]
Distilled water was added to the dried fine cellulose fibers so that the fine cellulose fibers were 0.5% by mass to prepare 20 g of a test dispersion. 20 g of the test dispersion was dispensed into a 30 ml glass vial, and then dispersed with a homogenizer (manufactured by IKA, trade name "Ultra Turrax T18", rotation speed 10,000 rpm, 5 minutes). Next, 7.2 ml of distilled water and 0.8 ml of the test dispersion were placed in a screw-cap test tube (inner diameter 12 mm), sealed, and manually shaken to make the dispersion uniform. The obtained dispersion was calculated according to the above-mentioned method for measuring the sedimentation height ratio.

<Production and evaluation of resin composite>
The obtained dried fine cellulose fiber and the following thermoplastic resin were melt-kneaded under the following conditions using a twin-screw extruder (OMEGA30H, L/D = 60) having 13 cylinder blocks so that the weight of the fine cellulose fiber was 1 part by mass per 9 parts by mass of the thermoplastic resin, to obtain pellets of fine cellulose fiber reinforced thermoplastic resin.

(Thermoplastic resin)
- UBE Nylon 1013B Polyamide 6 (hereinafter referred to as PA) manufactured by Ube Industries, Ltd.
The carboxyl end group ratio ([COOH]/[total end groups]) is 0.59.
- Prime Polypro J105G Made by Prime Polymer Polypropylene (hereinafter referred to as PP)

(Melt-kneading conditions)
Rotation speed: 300 rpm
Cylinder temperature: 250°C (for PA) or 200°C (for PP)

[Tensile yield strength, tensile yield elongation (TEy), tensile break elongation (TEb)]
Multipurpose test pieces conforming to ISO294-3 were molded using an injection molding machine with a maximum clamping pressure of 75 tons, and tests were performed under conditions conforming to JIS K6920-2 with n=10. Note that since polyamide resin changes due to moisture absorption, it was stored in an aluminum moisture-proof bag immediately after molding to suppress moisture absorption.
The ratio of the tensile elongation at yield (TEy) to the tensile elongation at break (TEb) [TEb/TEy] was calculated.

The fine cellulose fibers disclosed herein can impart favorable property-improving effects to resin composites, and can therefore be suitably used in fields such as automotive interior and exterior material applications.

Claims (13)

A fine cellulose fiber,
The average content of alkali-soluble polysaccharides in the fine cellulose fibers is 12.5% by mass or less,
The fine cellulose fibers have a ratio of the settling height of the fine cellulose fibers to the total liquid height of the test dispersion (100%) of 10% or more and 50 % or less when a test dispersion containing the fine cellulose fibers in water at a concentration of 0.05% by mass is allowed to stand at 23°C and normal pressure for 24 hours. The fine cellulose fibers according to claim 1, having an average fiber diameter of 2 to 1000 nm. The fine cellulose fibers according to claim 1 or 2, which are chemically modified. The fine cellulose fibers according to claim 3, wherein the chemical modification is acylation. The fine cellulose fiber according to any one of claims 1 to 4, having a weight average molecular weight (Mw) of 100,000 or more and a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of 6 or less. The fine cellulose fiber according to any one of claims 1 to 5, having an average alkali-soluble polysaccharide content of 12% by mass or less and a crystallinity of 60% or more. A dried body comprising the fine cellulose fibers according to any one of claims 1 to 6. The dried body according to claim 7, having a moisture content of 50% by mass or less. A resin composite comprising the fine cellulose fibers according to any one of claims 1 to 6 and a resin. A method for producing fine cellulose fibers according to any one of claims 1 to 6,
A cellulose raw material is pulverized and then defibrated with a homomixer to obtain a fine cellulose fiber slurry; and optionally, the fine cellulose fiber slurry is dried under reduced pressure while being stirred.
A method comprising: A method for producing a dried body according to claim 7 or 8,
A cellulose raw material is pulverized and then defibrated with a homomixer to obtain a fine cellulose fiber slurry;
drying the fine cellulose fiber slurry under reduced pressure while stirring; and optionally mixing the fine cellulose fiber slurry and/or the fine cellulose fibers with additional components.
A method comprising: A method for producing a resin composite according to claim 9,
A cellulose raw material is pulverized and then defibrated with a homomixer to obtain a fine cellulose fiber slurry; and optionally, the fine cellulose fiber slurry is dried under reduced pressure while being stirred.
A process for producing fine cellulose fibers by a method comprising the steps of:
A mixing step of mixing the fine cellulose fibers and the resin;
A method comprising: The method of any one of claims 10 to 12, further comprising chemically modifying the cellulose prior to, simultaneously with, and/or after the defibration.

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