Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F2/00—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B1/00—Preparatory treatment of cellulose for making derivatives thereof, e.g. pre-treatment, pre-soaking, activation
  • C08B1/006—Preparation of cuprammonium cellulose solutions
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B16/00—Regeneration of cellulose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
  • C08L1/02—Cellulose; Modified cellulose
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F11/00—Chemical after-treatment of artificial filaments or the like during manufacture
  • D01F11/02—Chemical after-treatment of artificial filaments or the like during manufacture of cellulose, cellulose derivatives, or proteins
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F2/00—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof
  • D01F2/02—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof from solutions of cellulose in acids, bases or salts
  • D01F2/04—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof from solutions of cellulose in acids, bases or salts from cuprammonium solutions
• • D—TEXTILES; PAPER
  • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B2201/00—Cellulose-based fibres, e.g. vegetable fibres
• • D—TEXTILES; PAPER
  • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B2201/00—Cellulose-based fibres, e.g. vegetable fibres
  • D10B2201/20—Cellulose-derived artificial fibres
  • D10B2201/22—Cellulose-derived artificial fibres made from cellulose solutions
• • D—TEXTILES; PAPER
  • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B2401/00—Physical properties
  • D10B2401/10—Physical properties porous
• • D—TEXTILES; PAPER
  • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B2505/00—Industrial
  • D10B2505/04—Filters

Definitions

• the present invention relates to cellulose fibers and products using the cellulose fibers.
• Cellulose is the most abundant carbohydrate on earth, a naturally occurring, biodegradable resource that is used in a variety of industrial fields. Furthermore, with the establishment of the Sustainable Development Goals (SDGs) in recent years, it is expected to become a sustainable resource with low environmental impact.
• SDGs Sustainable Development Goals
• One way to utilize cellulose is to make cellulose nanofibers, which are made by finely grinding cellulose.
• Cellulose nanofibers can be used in a variety of applications, including fillers for resins and rubbers, substrates for transparent materials and optical materials for electronic products, filtration materials, additives for foods, paints, and cosmetics, substrates for packaging materials and gas barrier materials, viscosity modifiers and dispersion stabilizers for various liquid products, and other applications.
• Cellulose nanofibers that meet the required performance requirements are being developed. By combining the selection of the type of cellulose used as the raw material, the selection of physical fine-grinding conditions, and the selection of chemical processing conditions, it is possible to obtain nanofibers made of cellulose materials with various shapes and characteristics.
• cellulose nanofibers have a strong coagulating effect due to intermolecular forces, and are prone to the formation of agglomerates due to aggregation during storage, the formation of agglomerates due to strong hydrogen bonds during drying, and the formation of agglomerates due to entanglement of fibers during stirring, kneading, etc.
• the viscosity can become too high, making it difficult to handle, and other problems can occur.
• powerful mechanical treatment or treatment with chemicals is required to reduce the size of the material, which increases costs. For these reasons, in applications where nanofibers are not required, they are sometimes used in the form of microfibers, which have a weaker micronization power.
• Patent Document 1 cellulose nanofibers are oxidized and then mixed with rubber latex to obtain a filler-rubber composite.
• the attempt is made to reduce the amount of coarse structures in the resulting rubber by increasing the viscosity of the latex, but as described in the examples, the rubber master batch contains a considerable amount of coarse structures of 10 ⁇ m or more in the dry state. This is presumably due to the generation of agglomerates resulting from the aggregation and entanglement of the nanofibers.
• cellulose microfibers are obtained by wet grinding using a cellulose raw material with a low hemicellulose content.
• the fiber diameter is adjusted by the conditions of wet grinding, but when the fiber is refined by grinding, either nanofiber formation or residual unground parts or both are unavoidable, and ultimately a considerable amount of coarse structures are included.
• the number average value of 50 fibers is calculated as the average fiber diameter, but the presence of nanofibers that cause agglomerates and the presence of unground parts are not evaluated.
• To confirm the dispersibility of cellulose fibers in the resin the presence or absence of coarse structures with a maximum diameter of 200 ⁇ m or more in a dry state is confirmed, but the presence or absence of coarse structures smaller than that is not evaluated.
• the cellulose raw material is first treated with an enzyme to break down the amorphous regions, and then refined to improve the homogeneity and dispersibility of the fibers, thereby obtaining cellulose microfibers.
• the fiber diameter, fiber length, and fibrillation rate are adjusted by the number of times the material is processed with the refiner, but even with this processing method, it is unavoidable to either turn the material into nanofibers or leave unground parts, or both, and the final product contains a considerable amount of coarse structures.
• Methods that solve this problem include adding a surfactant, removing water by solvent replacement and then drying, and chemically modifying cellulose.
• cellulose raw material is treated with an enzyme in advance to decompose the amorphous regions and then refined to obtain cellulose microfibers with a coefficient of variation of fiber diameter distribution of 1.1 or less.
• the maximum fiber diameter of CNF-B, which was refined weakly to obtain microfibers, was 1.271 ⁇ m, and no aggregates or undisintegrated parts were included in the 100 fibers observed, but the minimum fiber diameter was 0.022 ⁇ m and a considerable amount of nanofibers were included.
• Patent Document 5 a cationic surfactant is added to cellulose nanofibers, water is removed in the presence of a polyhydric alcohol, and at the same time, hydrophobization is performed with a silane coupling agent. Shear force is then applied to the rubber component to obtain a composite material that uses nanofibers but does not contain coarse structures larger than 1 ⁇ m.
• coalesced fibers in which the fibers are strongly bonded to each other are generated.
• These coalesced fibers are also a type of coarse structure, and depending on the application, they may impair the original performance of the microfiber.
• Patent Document 7 cellulose is dissolved in a cuprammonium solution and electrospinned to obtain uniform cellulose microfibers with a fiber diameter CV value of 11 to 30% and few particulate parts with a diameter of 3.0 ⁇ m or more.
• this method no unpulverized parts remain, cellulose is hardly oriented, and fibrillation is difficult, so even if it is used as a filler, nanofibers are unlikely to be generated during kneading.
• electrospinning is difficult to finely adjust the solidification rate, and the cellulose may reach the collector before sufficient desolvation is performed, resulting in the generation of coalesced fibers in which the fibers are firmly bonded to each other.
• the particulate parts in the sheet are 500 pieces/ mm2 or less, and there is a considerable amount of particulate parts when converted into weight units.
• the fibers obtained by electrospinning have problems such as low cellulose orientation, limited uses, strong aggregation during drying due to low crystallinity, and low productivity.
• the problem that the present invention aims to solve is to provide cellulose microfibers (fibrous cellulose) that have a uniform fiber diameter distribution with a low proportion of both cellulose nanofibers and coarse structures and that can be used for a variety of general purposes.
• the inventors conducted extensive research and experiments to solve the above problems, and discovered that the causes of the formation of coarse structures are the aggregation of nanofiberized cellulose, residual unpulverized parts of the raw cellulose, and strong adhesion between fibers. They unexpectedly discovered that by controlling these amounts to below a certain level, it is possible to obtain cellulose microfibers (fibrous cellulose aggregates) with few coarse structures and uniform fiber diameters without adding chemical substances or modifying the cellulose, and thus completed the present invention.
• the present invention is as follows.
• [1] Cellulose fibers having an average fiber diameter in a dry state of 0.3 ⁇ m or more and 3.0 ⁇ m or less when observed by an electron microscope, a ratio of fibers having a fiber diameter of less than 0.1 ⁇ m being 5% or less, and a ratio of coarse structures indexed by the ratio of the number of fibers having a wet fiber diameter of 20 ⁇ m or more as measured by automatic optical analysis being 3.0% or less.
• [3] The cellulose fiber according to [1] or [2] above, having a wet average fiber length of 3000 ⁇ m or less.
• [4] The cellulose fiber according to any one of [1] to [3] above, having a coefficient of variation of fiber diameter of 1.00 or less.
• [5] The cellulose fiber according to any one of [1] to [4] above, having a fiber diameter aggregation constant of 5.0 or less.
• [6] The cellulose fiber according to any one of [1] to [5], wherein the crystal structure of the cellulose constituting the cellulose fiber is type II.
• [7] Cellulose fiber according to any one of [1] to [6], wherein the crystallinity of the cellulose cellulose constituting the fiber is 30% or more and 90% or less.
• [8] A composition comprising the cellulose fiber according to any one of [1] to [7] above.
• [9] A porous body made of the cellulose fiber according to any one of [1] to [7] above
• the cellulose fibers of the present invention are uniform cellulose microfibers (fibrous cellulose aggregates) with few coarse structures, without the addition of chemical substances or modification of the cellulose, and can therefore be used for a variety of general-purpose applications, such as fillers for reinforcing resins and rubber, and as base materials for porous bodies such as filters.
• 1 is a SEM image of the cellulose fibers obtained in Example 1.
• 1 is a SEM image of the cellulose fibers obtained in Comparative Example 1.
• 1 is an SEM image of the cellulose fibers obtained in Comparative Example 7.
• 1 is a SEM image of the surface of a porous sheet prepared from the cellulose fibers of Example 1.
• 1 is an SEM image of the surface of a porous sheet prepared from the cellulose fibers of Comparative Example 7.
• 1 is a SEM-EDX image of a tensile fracture surface of a cellulose fiber-rubber composite in which the cellulose fiber of Example 1 is compounded.
• 1 is a SEM-EDX image of a tensile fracture surface of a cellulose fiber-rubber composite in which cellulose fibers of Comparative Example 6 are combined.
• 1 is an SEM image of the cellulose fibers obtained in Comparative Example 4.
• 1 is an SEM image of the cellulose fibers obtained in Comparative Example 8.
• 1 is an SEM image of the surface of a porous sheet prepared from cellulose fibers of Comparative Example 4.
• 1 is a SEM-EDX image of a tensile fracture surface of a cellulose fiber-rubber composite in which cellulose fiber of Example 1-3 is incorporated.
• One embodiment of the present invention is cellulose fibers having an average fiber diameter in a dry state of 0.3 ⁇ m or more and 3.0 ⁇ m or less when observed with an electron microscope, a ratio of fibers having a fiber diameter of less than 0.1 ⁇ m being 5% or less, and a ratio of coarse structures indexed by the ratio of the number of fibers having a wet fiber diameter of 20 ⁇ m or more measured by automatic optical analysis being 3.0% or less.
• cellulose fiber refers to a structure (aggregate) made of fibrous cellulose, and the method of producing the same is not particularly limited, and examples thereof include a method of finely pulverizing a cellulose raw material by physical force, a method of finely pulverizing by chemical force, and a method of dissolving the cellulose raw material in a solvent and forming it into a fibrous form. A combination of these methods is also possible.
• a method of dissolving the cellulose raw material in a solvent and forming it into a fibrous form is preferred. Dissolving the cellulose raw material in a solvent also makes it possible to remove minute foreign matter by filtration or centrifugation.
• fiber diameter of cellulose fibers refers to the value measured when the cellulose is in a dry state
• average fiber diameter refers to the number average value.
• the cellulose fibers of this embodiment are evaluated not only in a dry state but also in a wet state.
• evaluating in a dry state using an electron microscope it is difficult to distinguish between fibers that are originally aggregated and fibers that aggregate when dried.
• the results also vary depending on the location of the measurement. Furthermore, there is a limit to the number of fibers that can be measured in a dry state, and while there is a certain degree of accuracy in evaluating the average value, it is difficult to evaluate the distribution.
• the results of evaluation in a wet state are distinguished from the results of evaluation in a dry state by expressing the fiber diameter as the "wet fiber diameter" and the average fiber diameter as the "wet average fiber diameter". Note that since cellulose fibers swell in water, the "wet fiber diameter" is larger than the "fiber diameter”.
• the "average fiber diameter" of the "fiber diameter” of the cellulose fiber of this embodiment is 0.3 ⁇ m or more and 3.0 ⁇ m or less. If the average fiber diameter is 0.3 ⁇ m or more, it is possible to suppress the aggregation of fibers due to intermolecular forces during storage, aggregation due to entanglement during stirring, and aggregation due to hydrogen bonds during drying.
• the average fiber diameter is preferably 0.4 ⁇ m or more, more preferably 0.5 ⁇ m or more, and even more preferably 0.7 ⁇ m or more.
• the average fiber diameter is 3.0 ⁇ m or less, the number of fibers per unit weight increases, which has the effect of increasing the effect of adding as a filler and increasing the specific surface area when made into a porous body.
• the average fiber diameter is preferably 2.5 ⁇ m or less, more preferably 2.0 ⁇ m or less, even more preferably 1.5 ⁇ m or less, and most preferably 1.0 ⁇ m or less.
• the "proportion of fibers with a fiber diameter of less than 0.1 ⁇ m" of the cellulose fibers of this embodiment is 5% or less.
• the "proportion of fibers with a fiber diameter of less than 0.1 ⁇ m" is preferably 4% or less, more preferably 3% or less, even more preferably 2% or less, particularly preferably 1% or less, and most preferably 0%.
• cellulose nanofiber refers to cellulose fibers with a fiber diameter of less than 0.1 ⁇ m.
• cellulose microfiber refers to cellulose fibers with a fiber diameter of 0.1 ⁇ m or more and less than 9.7 ⁇ m.
• Coarse structure refers to a structure whose maximum width on the short side perpendicular to the long side is 20.0 ⁇ m or more in a wet state, as described below.
• Coarse structures include aggregates of structures smaller than 20.0 ⁇ m, such as aggregates of nanofibers and entangled fibers, and unified fibers in which fibers are firmly bonded to each other, as well as cellulose aggregates such as structures originally larger than 20.0 ⁇ m, such as remaining unground parts of cellulose raw materials and thick fibers, and foreign matter contained in the cellulose raw materials.
• the reason for using the measurement results in a wet state is that evaluation in a dry state makes it impossible to distinguish whether the structure was originally aggregated or aggregated when dried.
• measurement in a wet state makes it easier to increase the number of measurements, and allows for accurate evaluation of distribution.
• it depends on the preparation method and crystal structure of the cellulose fiber, by reducing the number of structures of 20.0 ⁇ m or more in a wet state, it is possible to reduce the number of structures of approximately 10.0 ⁇ m or more in a dry state.
• the "proportion of coarse structures" of the cellulose fibers of this embodiment is 3.0% or less. If the proportion of coarse structures is 3.0% or less, effects such as reduced defects when used as a filler, reduced defects when used as a base material for a porous body, and improved functionality by increasing the number of fibers can be expected.
• the "proportion of coarse structures” is preferably 2.0% or less, more preferably 1.0% or less, and even more preferably 0.5% or less. The smaller the "proportion of coarse structures," the better, but from the standpoint of production efficiency, a proportion of 0.1% or more is preferable.
• the "coefficient of variation of fiber diameter" of the cellulose fiber of this embodiment is preferably 1.00 or less. Fibers having a uniform fiber diameter with a coefficient of variation of fiber diameter of 1.00 or less are less susceptible to deterioration of function due to breakage of thin fibers and defects due to thick fibers, and are more likely to exhibit desired performance in various applications, and can have a uniform fiber length when shortened by physical impact.
• the "coefficient of variation of fiber diameter” is preferably 0.70 or less, more preferably 0.50 or less, even more preferably 0.40 or less, particularly preferably 0.30 or less, and most preferably 0.20 or less. The smaller the "coefficient of variation of fiber diameter", the more preferable it is, but from the viewpoint of production efficiency, a coefficient of variation of 0.05 or more is preferable.
• the "wet average fiber diameter" of the cellulose fiber of this embodiment is preferably 1.0 ⁇ m or more and 10.0 ⁇ m or less. By making the wet average fiber diameter 1.0 ⁇ m or more, it is possible to suppress the aggregation of fibers during storage, aggregation due to entanglement during stirring, and aggregation due to hydrogen bonds during drying.
• the "wet average fiber diameter” is preferably 1.3 ⁇ m or more, and particularly preferably 1.7 ⁇ m or more.
• the "wet average fiber diameter" is 10.0 ⁇ m or less, the number of fibers per unit weight increases, which has the effect of increasing the effect of adding as a filler and increasing the specific surface area when made into a porous body.
• the "wet average fiber diameter” is preferably 8.3 ⁇ m or less, more preferably 6.7 ⁇ m or less, even more preferably 5.0 ⁇ m or less, and particularly preferably 3.3 ⁇ m or less.
• aggregation constant is an index representing the degree of aggregation of cellulose fibers and is defined by the following formula.
• Coagulation constant (wet average fiber diameter ⁇ average fiber diameter)
• Cellulose fibers that contain many nanofibers with a fiber diameter of less than 0.1 ⁇ m appear to be dispersed when observed locally using an SEM, but in reality, some of the fibers are not crushed or a network structure is formed by hydrogen bonding. The wet fiber diameter of such cellulose fibers tends to be large.
• cellulose fibers that appear to be independent fibers overlapping each other using an SEM but in reality, many of the fibers are firmly bonded together, also tend to have a large wet fiber diameter.
• the "aggregation constant" of the cellulose fiber diameter is preferably 5.0 or less.
• the "aggregation constant” is more preferably 4.0 or less, even more preferably 3.0 or less, and particularly preferably 2.5 or less.
• a smaller “aggregation constant” is preferable, from the viewpoint of production efficiency, it is preferably 1.0 or more, and more preferably 1.5 or more.
• the "coefficient of variation of wet fiber diameter" of the cellulose fiber of this embodiment is preferably 1.00 or less. Fibers with a uniform fiber diameter, with a coefficient of variation of wet fiber diameter of 1.00 or less, are less susceptible to loss of function due to breakage of thin fibers and defects due to thick fibers, and are more likely to exhibit the desired performance in various applications. In addition, the fiber length can be made uniform when shortening the fibers by physical impact.
• the "coefficient of variation of wet fiber diameter” is preferably 0.90 or less, more preferably 0.80 or less, even more preferably 0.70 or less, particularly preferably 0.60 or less, and most preferably 0.50 or less. A smaller "coefficient of variation of wet fiber diameter" is preferable, but from the viewpoint of production efficiency, a value of 0.20 or more is preferable.
• the "crystal structure (crystal form)" of the cellulose fiber of this embodiment is not particularly limited, and various cellulose types, such as type I, type II, type III, and type IV, can be used.
• the "degree of crystallinity" of the cellulose fiber according to the present invention is also not particularly limited, and cellulose fibers of any degree of crystallinity can be used. When adjusting the fiber length in a wet state, a type II crystal structure is preferred, which allows the fibers to be cut with a weak force and tends to be uniform.
• the "crystallinity" of the cellulose fiber in this embodiment is preferably 30% or more and 90% or less. If the crystallinity is a certain level or more, aggregation during drying can be reduced and the strength of the cellulose fiber will also be high, so the crystallinity is preferably 30% or more, more preferably 40% or more, and particularly preferably 50% or more. On the other hand, if the crystallinity is below a certain level, dispersibility when used as a filler will improve, and when used as a base material for a porous body, fibers will bond at their intersections to increase the strength of the base material, so the crystallinity is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less. Note that several methods have been proposed for calculating the crystallinity of cellulose, but in this embodiment, the crystallinity refers to the crystallinity calculated by the Segal method.
• the cross-sectional shape of the cellulose fibers in this embodiment is not particularly limited, and fibers of various cross-sectional shapes such as round, irregular, and irregular can be used, and the surface may be fibrillated.
• a round cross section is preferred from the perspective of the reinforcing effect when used as a filler and the repair effect when the porous body is used as a filter.
• the surface is fibrillated in order to prevent the fibers from coming off.
• the "fiber length” and "wet fiber length” of the cellulose fibers of this embodiment can be adjusted to any length.
• it can be obtained in the form of very long fibers, or it can be obtained in the form of short fibers by cutting the obtained long fibers.
• the fiber length and wet fiber length can be selected according to the application. Note that the "average fiber length” and “wet average fiber length” in this invention represent the length-weighted average fiber length.
• the "wet average fiber length" is preferably 20 ⁇ m or more and 3000 ⁇ m or less. If the wet average fiber length is a certain level or more, the fibers are less likely to come off even when stress is applied, and the reinforcing effect is high, so it is more preferably 30 ⁇ m or more, even more preferably 40 ⁇ m or more, and particularly preferably 50 ⁇ m or more.
• the wet average fiber length is a certain level or less, the number of fibers increases, resulting in a high reinforcing effect, and the generation of coarse structures due to entanglement of fibers during kneading can be suppressed, so it is more preferably 1000 ⁇ m or less, even more preferably 800 ⁇ m or less, even more preferably 600 ⁇ m or less, and particularly preferably 400 ⁇ m or less.
• the "wet average fiber length" is preferably 50 ⁇ m or more and 3000 ⁇ m or less. If the wet average fiber length is a certain level or more, the fibers are kept entangled and the porous structure can be maintained even if drying shrinkage occurs during drying, so the wet average fiber length is more preferably 100 ⁇ m or more, and even more preferably 200 ⁇ m or more.
• the wet average fiber length is a certain level or less, entanglement of the fibers can be suppressed, so the wet average fiber length is more preferably 2000 ⁇ m or less, even more preferably 1000 ⁇ m or less, and particularly preferably 800 ⁇ m or less.
• the "coefficient of variation of wet fiber length" of the cellulose fiber of this embodiment is preferably 1.00 or less. Fibers having a uniform fiber length with a coefficient of variation of wet fiber length of 1.00 or less can suppress the generation of agglomerates due to fiber entanglement. As a result, the desired performance can be exhibited when used in various applications.
• the "coefficient of variation of wet fiber length" is more preferably 0.90 or less, even more preferably 0.80 or less, particularly preferably 0.70 or less, and most preferably 0.60 or less. The smaller the "coefficient of variation of wet fiber length" is, the more preferable it is, but from the viewpoint of production efficiency, a value of 0.05 or more is preferable.
• the cellulose fibers of this embodiment can be made uniform in both fiber diameter and fiber length, and by making both uniform, the effect of using the fibers in various applications can be efficiently achieved.
• the "coefficient of variation of wet fiber diameter" and the "coefficient of variation of wet fiber length” are both 1.00 or less.
• both are 0.90 or less, more preferably both are 0.80 or less, even more preferably both are 0.70 or less, particularly preferably both are 0.60 or less, and especially preferably both are 0.50 or less.
• both the "coefficient of variation of wet fiber length" and the "coefficient of variation of wet fiber length" are smaller, but from the viewpoint of production efficiency, it is preferable that they are 0.05 or more.
• the cellulose fibers of this embodiment can be converted into cellulose derivatives by reacting some of their hydroxyl groups, and any substituent can be introduced depending on the required functions.
• a substituent that does not cause hydrophobization of cellulose is preferred, and the degree of substitution is preferably 0.30 or less, more preferably 0.20 or less, particularly preferably 0.10 or less, and particularly preferably 0.05 or less.
• the cellulose fibers of this embodiment can be used as an aqueous solution dispersed in water as necessary.
• Surfactants, inorganic salts, water-soluble polymers, etc. may also be added, and other liquids compatible with water may be added if necessary, or the fibers may be dispersed in a non-aqueous solvent.
• the fibers may be mixed with other fibers or solids such as particles and fillers.
• anionic, amphoteric, or nonionic surfactants are preferred in terms of improving the biodegradability of cellulose and the environmental impact after decomposition, and the amount used is preferably 10% by weight or less. More preferably, the amount is 3% by weight or less, even more preferably 1% by weight or less, and particularly preferably 0.1% by weight or less. It is most preferable to not add any surfactant.
• the cellulose fibers of this embodiment can be used in a dried solid state as necessary. To prevent aggregation during drying, freeze drying, solvent replacement drying, solvent replacement freeze drying, supercritical drying, etc. may be performed. Surfactants, inorganic salts, oils, etc. may be added, and cellulose derivatives may be made by utilizing the hydroxyl groups of cellulose.
• the cellulose raw material is not particularly limited, and various raw materials can be selected.
• wood pulp, non-wood pulp, cotton-based pulp such as cotton and cotton linters, cellulose such as sea squirt and seaweed, recovered pulp, recycled cellulose, etc. can be mentioned. It is also possible to use a mixture of two or more of them. Among them, cotton and cotton linter pulp are preferred because of their high purity, and cotton linters are particularly preferred.
• the solvent for dissolving cellulose is not particularly limited, and various known solvents can be selected. Examples include cuprammonium solution, viscose solution, acids or alkalis of specific concentrations, aqueous solutions of inorganic salts such as zinc chloride, N-methylmorpholine N-oxide, and various ionic liquids. Among these, cuprammonium is preferred as a solvent because it allows the coagulation rate to be adjusted, the fiber diameter to be easily narrowed, and fibrillation to be adjusted.
• spinning there are no particular limitations on the method of dissolving cellulose in a solvent and forming it into a fiber form, and various spinning methods can be used.
• flow-down tension spinning in which a solution is extruded from a spinning nozzle with many holes (orifices) and flows into a funnel together with a coagulating liquid that removes the solvent, and coagulated
• air-gap spinning in which the solution is once discharged into the air and stretched, and then coagulated with a coagulating liquid
• dry spinning in which stretching and desolvation are performed in air
• melt-blow spinning in which stretching and coagulation are performed using a high-speed air flow
• electrospinning in which the solution is charged and thinned and accumulated by electrical repulsion.
• flow-down tension spinning air-gap spinning, and melt-blow spinning, which can control the orientation of cellulose, are preferred, and flow-down tension spinning, which can uniformize the fiber diameter, is less likely to break even when the fiber diameter is thin, and can suppress strong adhesion between the fibers, is particularly preferred.
• cellulose is dissolved in a cuprammonium solution and tension spinning is performed.
• concentration of cellulose dissolved in the cuprammonium solution can be selected arbitrarily. Although it depends on the degree of polymerization of the cellulose to be dissolved, 1 to 20% by weight is preferable. After dissolving the cellulose, it is preferable to remove foreign matter and undissolved matter by performing filtration through a filter or centrifugation. If the concentration is at a certain level or higher, the viscosity of the stock solution increases and thread breakage in the funnel is suppressed, which results in uniform drawing and an effect of preventing the single threads from coming into contact with other fibers before sufficient solvent removal occurs, resulting in a uniform fiber diameter.
• the concentration of cellulose dissolved in the cuprammonium solution is more preferably 2% by weight or more, even more preferably 3% by weight or more, and particularly preferably 4% by weight or more. If the concentration is below a certain level, the fiber diameter can be narrowed by being easily stretched, and foreign matter can be easily removed by filtering or centrifuging the raw solution.
• the concentration of cellulose dissolved in the cuprammonium solution is more preferably 9% by weight or less, even more preferably 8% by weight or less, and particularly preferably 7% by weight or less.
• the ammonia concentration is preferably 10% by weight or less, more preferably 9% by weight or less, and even more preferably 8% by weight or less. Within this range, coagulation unevenness is unlikely to occur, and strong bonding between fibers can be suppressed.
• Nozzles of any shape can be used for ejecting the dissolving liquid.
• the number of holes is preferably 10 to 2000. If the number of holes is 2000 or less, the occurrence of internal and external differences in coagulation can be kept within a certain range, resulting in uniform fiber diameters. In addition, by keeping the flow rate of the coagulating liquid below a certain level, the flow in the funnel can be rectified, and contact between fibers can be suppressed before sufficient desolvation has been achieved.
• the number of holes is more preferably 1500 or less, even more preferably 1000 or less, and particularly preferably 500 or less. From the viewpoint of productivity, the number of holes is more preferably 50 or more.
• the hole diameter is preferably 0.05 to 0.50 mm.
• the hole diameter is 0.05 or more, productivity is high, sufficient stretching can be achieved, and the strength of the cellulose fibers can be increased.
• the ejection speed of the dissolving liquid can be kept below a certain level, which prevents the dissolving liquid from shaking in the coagulating liquid and prevents the fibers from contacting each other before sufficient desolvation has been achieved.
• the hole (hole) diameter is more preferably 0.08 mm or more, and even more preferably 0.10 mm or more. On the other hand, if the hole (hole) diameter is 0.50 mm or less, the solution discharged from the spinneret can be kept at a certain distance, and contact between fibers before sufficient desolvation can be suppressed.
• the hole (hole) diameter is more preferably 0.40 mm or less, and even more preferably 0.30 mm or less.
• the hole (hole) distance from end to end of adjacent holes (holes) is preferably 0.60 to 2.00 mm. If the hole (hole) distance is 0.60 mm or more, contact between fibers can be suppressed even if the dissolving solution shakes slightly in the coagulation solution.
• the spinneret since the spinneret has holes arranged concentrically or in multiple rows, the dissolving liquid discharged from the holes in the outermost layer comes into contact with fresh coagulation liquid, but the dissolving liquid discharged from the holes in the inner layer may have uneven coagulation. If the distance between the holes is 0.60 mm or more, the coagulation liquid is more likely to diffuse into the inner layer, which can suppress uneven coagulation of the dissolving liquid discharged from the holes in the inner layer, and as a result, it is possible to suppress contact between the fibers before sufficient desolvation is achieved.
• the distance between the holes is more preferably 0.80 mm or more, and even more preferably 1.0 mm or more.
• the type of coagulation liquid is not important as long as it is a liquid that can perform deammonification, but it is preferable to use water with an adjusted temperature from the viewpoints of economy and safety.
• the type of coagulation liquid is not important as long as it is a liquid that can perform deammonification, but it is preferable to use water with an adjusted temperature from the viewpoints of economy and safety.
• it is necessary to perform drawing at a low spinning temperature but the coagulation of the solution discharged from the holes in the inner layer may be insufficient.
• copper removal is performed in this state, strong hydrogen bonds will be formed between the fibers. For this reason, it is preferable to first perform drawing and coagulation at a low spinning temperature, and then complete the coagulation of the solution discharged from the holes in the inner layer at a higher spinning temperature. After deammonification in the funnel and fiber formation, the copper removal can be performed by any method.
• the method of pouring acid into the funnel the method of discharging the blue yarn into an acid bath after it leaves the funnel, the method of changing the orientation of the blue yarn after it leaves the funnel and immersing it in an acid bath, the method of dripping acid onto the blue yarn, the method of receiving the blue yarn on a net and showering it with acid, the method of receiving the blue yarn in a tank and adding acid in a batch-type manner, and the like can be mentioned.
• the cellulose fiber is less likely to be fibrillated.
• the acid between the fibers is easily renewed, the copper removal efficiency is improved, and cellulose fibers with less residual copper and residual sulfuric acid can be obtained.
• a method of receiving the blue yarn on a net after it leaves the funnel and relaxing the tension, and a method of showering sulfuric acid on the blue yarn after it leaves the funnel and changing the orientation of the blue yarn to suppress an increase in tension were used.
• deammonification is performed by a method in which cellulose is not sufficiently stretched, such as electrospinning, the strength of the obtained cellulose fiber can be increased by applying a certain amount of tension to perform copper removal.
• the method for removing the acid can be selected arbitrarily.
• the fibers are thin and the liquid between the fibers is not easily renewed, so a method that allows easy liquid renewal is preferable.
• washing with warm water was repeated to remove sulfuric acid. It is preferable that the residual copper and sulfuric acid content of cellulose fibers is low. If these contents are high, they can cause the fibers to clump together when dried, reduce strength during storage, and slow the rate of biodegradation.
• any method can be selected. For example, heat drying, reduced pressure drying, air drying, freeze drying, solvent replacement drying, supercritical drying, or a combination of these methods can be used.
• An oil agent can be added during drying to suppress aggregation.
• the fiber diameter of the cellulose fibers can be adjusted as desired by adjusting the concentration of the dissolved cellulose, the diameter of the nozzle for discharging the dissolved solution, the shape of the funnel, and the stretching ratio determined by the combination of the temperature, composition, and flow rate of the coagulation liquid.
• Various methods can be used to adjust the fiber length of cellulose fibers depending on the required fiber length, including cutting the fibers with a blade and subjecting the fibers to a physical impact to shorten the fibers.
• Examples of methods for cutting cellulose fibers with a blade include a rotary cutter, a guillotine cutter, and a cutter mill.
• the cellulose fibers may be cut in a dry state, a wet state, or a state suspended in water or an organic solvent. They may also be chemically or heat-treated in advance. Cutting with a blade makes it easy to keep the fiber length constant, but there is a limit to how short the fiber can be.
• Examples of the method of fiber shortening by physical impact include mixers, homogenizers, ball mills, beaters, disc finers, grinders, high-pressure homogenizers, etc.
• the method of fiber shortening by physical impact can shorten the fiber length, but the fiber length of the obtained fiber is likely to have a certain distribution.
• the fiber length of the obtained fiber is likely to have a certain distribution.
• a distribution of fiber diameters occurs, and a distribution of fiber length is likely to occur because thin and easily cut parts and thick and difficult to cut parts are mixed.
• the cellulose of the present application has a uniform fiber diameter, the spread of the fiber length distribution can be suppressed to a certain extent.
• the fiber length distribution can be further suppressed by cutting the long fibers to a certain length with a blade before applying a physical impact, rather than immediately shortening the long fibers.
• the purpose of applying a physical impact to the fibers is to shorten the fiber length or to peel off the fibers that are weakly associated with each other, and not to reduce the fiber diameter. If it is desired to shorten the fiber length very much, it is preferable to combine it with a method such as suppressing the orientation of cellulose or lowering the degree of polymerization of cellulose in order to suppress fiber fibrillation as necessary.
• the cellulose fiber of the present embodiment can be used as a filler to be added to resins or rubbers, a porous body that can be used in filters, adsorbents, sound absorbing materials, heat insulating materials, etc., a coating agent, a base material for artificial leather, an anti-settling agent for liquid products, etc.
• Cellulose fibers that have few nanofibers and few coarse structures can be uniformly dispersed as a filler and a uniform porous body can be obtained without adding a surfactant or making the cellulose hydrophobic.
• the present invention is not limited thereto.
• the cellulose fibers of this embodiment may be used alone, may be mixed with other cellulose fibers or fibers of other materials, or may be laminated with another porous body.
• an example of forming a porous body using cellulose fibers alone is described.
• no surfactant or pore size retaining agent is added, and the cellulose is not hydrophobized. Instead, a sheet is formed by the simplest method of heating and drying, and the effect of the shape of the cellulose fibers on the formation of the porous body is evaluated.
• the method for forming a porous body from cellulose fibers is not particularly limited, and various known methods can be used. For example, air-laid method, spunlace method, needle punch method, papermaking method, chemical bond method, freeze-drying method, etc. are included.
• the papermaking method is preferred in that it is a simple method for obtaining a homogeneous porous body.
• the liquid in which the cellulose fibers are suspended during papermaking is preferably one in which the cellulose does not aggregate.
• water is preferable, but from the viewpoints of drying efficiency and suppression of aggregation during drying, alcohols such as methanol, ethanol, isopropyl alcohol, and t-butanol, ketones such as acetone and methyl ethyl ketone, and ethers such as diethyl ether are also preferable.
• alcohols such as methanol, ethanol, isopropyl alcohol, and t-butanol
• ketones such as acetone and methyl ethyl ketone
• ethers such as diethyl ether
• the method of drying after papermaking is not particularly limited, but when the crystal structure of the cellulose fibers is type II, the temperature is preferably 200° C. or less, more preferably 190° C. or less, and even more preferably 180° C. or less.
• the obtained cellulose fiber sheets were used to evaluate their performance as porous bodies.
• the material to be mixed is not particularly limited, and it can be used as a filler for various resins and rubbers.
• natural rubber latex and cellulose fiber are mixed to prepare a master batch, kneaded, and then vulcanized and hot-pressed to obtain a composite of cellulose fiber and rubber.
• the solvent replacement or freeze-drying of the cellulose fiber, the addition of surfactants or polyhydric alcohols, the hydrophobization of cellulose, the addition of other fillers, etc. are not performed, and the composite is performed by a simple method, and the effect of the shape of the cellulose fiber on the composite is evaluated.
• the cellulose fibers When mixing the cellulose fibers and natural rubber latex, the cellulose fibers may be added in a dry state, or in a slurry state suspended in water or an organic solvent. To disperse the cellulose fibers more uniformly, it is preferable to add them in a slurry state.
• a planetary centrifugal mixer When mixing the cellulose fibers and natural rubber latex, it is preferable to use a planetary centrifugal mixer. The resulting aqueous solution in which the natural rubber latex and cellulose fibers are suspended is dried to prepare a master batch.
• the cellulose concentration in the masterbatch is preferably 1.0 to 20.0% by weight or more. Since cellulose has high dispersibility and is difficult to form a network structure in the presence of water, if the cellulose concentration is low, the cellulose fibers will settle during drying, resulting in poor uniformity of the obtained masterbatch.
• the lower limit of the cellulose concentration in the masterbatch is more preferably 1.5% by weight or more, and even more preferably 2.0% by weight or more.
• the method for kneading the obtained master batch can be a known method. For example, a Banbury mixer or an oven roll can be used. After kneading the master batch, stearic acid, zinc oxide, sulfur, and a vulcanization accelerator are added and further kneaded.
• Carbon black or the like may be added as necessary.
• vulcanization and molding are performed by hot pressing and cold pressing to obtain a composite of cellulose fiber and rubber.
• the temperature of the series of operations is preferably 200° C. or less, more preferably 190° C. or less, and even more preferably 180° C. or less.
• the obtained composite is punched into a dumbbell shape and the composite is evaluated.
• the cellulose fiber of this embodiment has biodegradability and decomposes in compost, soil, and the ocean. Biodegradation in the ocean is particularly difficult due to the small number of microorganisms and the low temperature rise, so in order to speed up the decomposition rate in the ocean, it is preferable that the cellulose is not hydrophobically modified. Also, considering the safety of the decomposition products, it is preferable not to add surfactants or additives for various applications.
• the solid content concentration of the cellulose fibers in the pure water is adjusted to 0.10 to 0.01% by weight, and the cellulose fibers are precipitated by centrifugation and resuspended in ethanol three times to replace the solvent with ethanol.
• the cellulose fibers are further precipitated by centrifugation and resuspended in t-butanol three times to replace the solvent with t-butanol.
• the sample is freeze-dried and vapor-deposited with osmium to obtain an observation sample. This sample is observed with an electron microscope at a magnification of 1000x, 10000x, or 30000x depending on the fiber diameter.
• two diagonal lines are drawn on the observation image, and one straight line is arbitrarily drawn passing through the intersection of the diagonal lines, and the widths of 25 fibers intersecting with this straight line are visually measured.
• the observation location is changed and another location is enlarged and the same measurement is performed, observing a total of four locations, and the average value is calculated from the widths of a total of 100 fibers to obtain the average fiber diameter.
• the fiber width if two or more fibers are found to be attached and there is no separated portion within the field of view of the image, they are considered to have been attached at the sample preparation stage, and the width of each fiber is measured as if they were separate fibers.
• the wet average fiber diameter is measured by optical automatic analysis using a Valmet FS5 Fiber Image Analyzer. However, accurate measurements cannot be made for fibers with a diameter that is too small because the resolution is not sufficient to measure the diameter.
• Cellulose fibers with an average fiber diameter of 0.3 ⁇ m or less measured by an electron microscope are listed as reference values.
• the solids concentration of cellulose fiber in pure water is automatically adjusted to a range of 0.005 to 0.0005% by weight using "Valmet FS5", 300 cc is placed in a plastic beaker, and the mixture is dispersed in the beaker for 1 minute using a bath-type ultrasonic disperser.
• the mixture is then placed in the Valmet FS5, and various parameters are set as follows, and measurements are performed.
• the fiber width (unit: ⁇ m) obtained as a result of the measurement is used as the wet average fiber diameter.
• the wet average fiber diameter cannot be measured by automatic optical analysis within the range of 0.005 to 0.0005% by weight of the solids concentration of cellulose fiber in pure water
• the solids concentration is increased by 0.005% by weight from 0.005% by weight, and the wet average fiber diameter is measured while changing the concentration to 0.010% by weight, 0.015% by weight, 0.020% by weight, and 0.025% by weight.
• concentration is too high to be measured, automatic adjustment is performed, and the value that remains constant even when the concentration is changed is regarded as the wet average fiber diameter.
• Fiber diameter aggregation constant (wet average fiber diameter) ⁇ (average fiber diameter)
• the aggregation constant of the fiber diameter is calculated by:
• Crystallinity (%) ⁇ (diffraction intensity of 200 plane) ⁇ (diffraction intensity of amorphous part) ⁇ (diffraction intensity of 200 plane) ⁇ 100
• the crystallinity (%) is calculated by the following.
• aqueous suspension with a cellulose fiber concentration of 0.10% by weight in pure water is prepared, a cellulose filter paper is placed on a Büchner funnel, and the suspension is filtered while reducing the pressure to 0.01 MPa so that the cellulose amount is 40 g/ m2 to remove water, and the resulting laminated sheet of cellulose fiber and filter paper is dried at 110°C for 1 hour. After drying, the cellulose fiber layer is peeled off from the filter paper to obtain a cellulose fiber sheet.
• the surface is evaluated for the presence of coarse structures having a size of 10 ⁇ m or more in a dry state according to the following criteria.
• "X” Coarse structures are present on all three sheets.
• ⁇ Coarse structures are present on one or two of the three sheets.
• ⁇ No coarse structures are present on any of the three sheets.
• aqueous suspension with a cellulose fiber concentration of 5.0% by weight in pure water is prepared, and added to natural rubber latex with a solids concentration of 60.0% by weight so that the weight ratio of natural rubber to cellulose fiber is 20: 1.
• the resulting mixture is stirred with a planetary stirrer, and the resulting wet master batch is spread thinly on a Teflon (registered trademark) vat and dried at 50°C for 48 hours, and further dried in a vacuum dryer for 3 hours to obtain a master batch.
• Teflon registered trademark
• the obtained master batch is pre-kneaded for 5 minutes at 50°C and 20 rpm using a Labo Plastomill, and then 0.5 g of stearic acid, 6.0 g of zinc oxide, 3.5 g of sulfur, and 0.7 g of vulcanization accelerator per 100 g of master batch are added, and further kneaded for 10 minutes at 50°C and 40 rpm to obtain a bulk composite.
• the obtained composite is hot-pressed for 8 minutes at 150°C and 30 MPa using a heated hydraulic press, and further cold-pressed for 5 minutes at 20°C and 10 MPa to obtain a sheet-shaped cellulose fiber-rubber composite with a thickness of about 2 mm.
• Example 1 Cotton linter pulp was dissolved in a cuprammonium solution to prepare a cuprammonium cellulose solution having a cellulose concentration of 5.0 wt%, a copper concentration of 1.8 wt%, and an ammonia concentration of 5.5 wt%, which was then filtered through a sintered filter having an average pore size of 5 ⁇ m to remove foreign matter.
• the cuprammonium cellulose solution was discharged into 20°C warm water from a spinneret having a discharge hole with a hole diameter of 0.3 mm, 180 holes, and a hole distance of 1.1 mm as a spinning nozzle, and stretched and deammonified by a flow-down tension spinning method to produce a blue yarn.
• the blue yarn and the warm water were received while running 50°C warm water in a semicircular inclined trough installed 20 cm below the funnel outlet, and the blue yarn and the warm water were separated by pouring them into a plastic net.
• the blue yarn was showered with 10% by weight sulfuric acid to thoroughly decopper it, and then showered with pure water to thoroughly wash off the sulfuric acid, and a continuous cellulose fiber in a wet state was obtained.
• the obtained continuous cellulose fibers were diluted with pure water to prepare an aqueous suspension with a cellulose concentration of 1.0% by weight, and 500 ml of the suspension was placed in a mixer (Extreme Mill, MX-1200XT, manufactured by AS ONE Corporation) and treated for 5 minutes to prepare short cellulose fibers.
• Example 2 Short cellulose fibers were prepared in the same manner as in Example 1, except that the ammonia concentration of the cuprammonium cellulose solution was 8.0% by weight.
• Example 3 Short cellulose fibers were prepared in the same manner as in Example 2, except that the cuprammonium cellulose solution had a cellulose concentration of 4.0% by weight and a copper concentration of 1.4% by weight.
• Example 4 Short cellulose fibers were prepared in the same manner as in Example 1, except that the ammonia concentration of the cuprammonium cellulose solution was 4.5% by weight.
• Example 5 Short cellulose fibers were prepared in the same manner as in Example 4, except that the cuprammonium cellulose solution had a cellulose concentration of 7.0% by weight and a copper concentration of 2.5% by weight.
• Example 6 The shortened cellulose fibers obtained in Example 1 were subjected to five micronization treatments under an operating pressure of 100 MPa using a high-pressure homogenizer (NS015H manufactured by Nia Sorobi) to prepare shortened cellulose fibers.
• a high-pressure homogenizer (NS015H manufactured by Nia Sorobi) to prepare shortened cellulose fibers.
• Example 7 The shortened cellulose fibers obtained in Example 1 were suspended in 10% by weight sulfuric acid to a cellulose concentration of 0.1% by weight, heated to 70°C and stirred with a magnetic stirrer for 30 minutes, and the sulfuric acid was washed out with pure water to obtain cellulose fibers that had been subjected to a fibrillation treatment. The obtained cellulose fibers were treated with a high-pressure homogenizer in the same manner as in Example 7 to prepare shortened cellulose fibers.
• Example 8 The cuprammonium cellulose solution had a cellulose concentration of 7.0% by weight and a copper concentration of 2.5% by weight, and was stirred overnight in an oxygen atmosphere to reduce the degree of polymerization of the cellulose.
• Continuous cellulose fibers were prepared in the same manner as in Example 1, and then the solution was subjected to a micronization treatment using a high-pressure homogenizer in the same manner as in Example 6 to prepare short cellulose fibers.
• Example 9 A spinneret having an outlet hole with a hole diameter of 0.3 mm, 800 holes, and a hole distance of 1.1 mm was used as a spinning nozzle, the blue yarn coming out of the funnel outlet was deflected, hot water of 50°C was poured on it, the tension of the blue yarn was reduced by adjusting the speed with a nip roller, and copper was removed by dropping 10% by weight of sulfuric acid onto the blue yarn running freely in the horizontal direction with a nozzle, and then the yarn was immersed in a bath of pure water flowing countercurrently to wash off the sulfuric acid, thereby obtaining cellulose fiber wound into a skein.
• the obtained skein-wound cellulose fiber was cut using a rotary cutter with multiple cutting blades arranged radially at a pitch of 1 mm to prepare short cellulose fiber. Furthermore, when the blue thread that had turned and was running freely sideways was touched with a fingertip, the surface of the thread was smooth, suggesting that the single threads were not firmly bonded to each other.
• Example 10 The short fiber cellulose fibers obtained in Example 9 were treated with a high pressure homogenizer in the same manner as in Example 6 to prepare short fiber cellulose fibers.
• Example 11 The shortened cellulose fibers obtained in Example 2 were subjected to five micronization treatments under an operating pressure of 50 MPa using a high-pressure homogenizer (NS015H manufactured by Nia Sorobi) to prepare shortened cellulose fibers.
• a high-pressure homogenizer (NS015H manufactured by Nia Sorobi) to prepare shortened cellulose fibers.
• Comparative Example 2 The cellulose fibers obtained in Comparative Example 1 were treated with a high-pressure homogenizer in the same manner as in Example 6 to prepare short cellulose fibers.
• Electrostatic spinning was performed using a metal nozzle with an inner diameter of 0.41 mm, and the cellulose fibers were separated from the collector by decoppering with sulfuric acid, and the sulfuric acid, PEG, and surfactant were washed with pure water, and the mixture was shortened in a mixer in the same manner as in Example 1 to prepare shortened cellulose fibers.
• the fiber of Comparative Example 5 had a fiber diameter of 0.1 ⁇ m or less measured in a dry state of 99%, and a coarse structure with a wet fiber diameter of 20 ⁇ m or more measured in a wet state of 1.4%. This is because, although the total exceeds 100%, the coarse structure may not be included in the measurement field of view when a very small portion is enlarged with an electron microscope. In addition, fibers that appear independent in an image in which a very small portion is enlarged may be connected in an invisible part of the image.
• the cellulose fibers obtained in Examples 1 to 10 are microfibers in terms of average fiber diameter, but because the proportion of nanofibers is small, they are highly stable fibers with a small aggregation constant of fiber diameter, and furthermore, the proportion of coarse structures is small, and they are uniform fibers with a small coefficient of variation of fiber diameter. Furthermore, as in Examples 1 to 5, the fiber diameter can be freely controlled by adjusting the spinning conditions, and as in Examples 6 to 10, the fiber length can be freely controlled while maintaining the fiber diameter by adjusting the micronization conditions. In contrast, the fibers of Comparative Examples 1, 4, and 8 obtained by the existing spinning method, even though the same wet spinning method was used, have a certain amount of coarse structures.
• the cellulose fibers are strongly bonded to each other immediately after spinning, and even if a crushing treatment is performed as in Comparative Example 2, a certain amount of coarse structures remain, and nanofibers are generated by fibrillation.
• the cellulose fiber of Comparative Example 8 like Comparative Example 1, also has the cellulose fibers strongly bonded to each other immediately after spinning.
• a certain amount of nanofiber parts and coarse structures are present.
• the cellulose fiber of Example 1 maintained gaps between the fibers even after drying by heating, resulting in a uniform porous sheet.
• the cellulose fiber of Comparative Example 7 contained nanofibers and was short in length, and the gaps between the fibers were filled by shrinkage during drying, resulting in a sheet that did not have a uniform porous structure.
• Table 2 in the sheets prepared from the cellulose fibers having a high proportion of nanofibers obtained in Comparative Examples 5 and 6, the gaps between the fibers are filled to such an extent that the air resistance cannot be measured, and the structure cannot be said to be porous.
• the fibers of Comparative Examples 5 and 6 which have short fiber lengths, the fibers are disentangled during drying, and the gaps between the fibers are easily filled.
• the sheets prepared from the cellulose fibers of Comparative Examples 4 and 7, which have a large number of coarse structures, contain coarse structures in the sheets, and are prone to defects such as pinholes and reduced strength.
• the fracture surface of the cellulose fiber-rubber composite obtained from the cellulose fibers of Example 1 shows good dispersion of the cellulose fibers
• the fracture surface of the composite obtained from the cellulose fibers in Comparative Example 6, in which coarse structures are present shows scattered cellulose lumps.
• the cellulose fiber-rubber composites obtained from the cellulose fibers of Examples 1 to 8 and 11 have improved tensile strength without a decrease in breaking elongation, and because they have a constant fiber length, they can also improve 100% stress like the compounding agent containing type I cellulose.
• the composites obtained from the cellulose fibers containing coarse structures of Comparative Examples 4 to 7 tend to have a decrease in breaking elongation and a decrease in tensile strength.
• the cellulose fiber of Example 1 maintains good dispersion even when the blending amount is increased. Also, as is clear from Table 4, the tensile strength is maintained even when the blending amount of cellulose fiber is 10% by weight, and the stress can be improved by 100% depending on the blending amount.
• the cellulose fibers of the present invention are uniform cellulose microfibers (fibrous cellulose aggregates) with few coarse structures, without the addition of chemical substances or modification of cellulose, and can therefore be used for a variety of general purposes, such as fillers for reinforcing resins and rubber, and as base materials for porous bodies such as filters.
• the cellulose fibers of the present invention can also be suitably used as materials for porous bodies such as adsorbents, sound-absorbing materials, and heat insulating materials, as base materials for transparent materials and optical materials for electronic products, as additives for foods, paints, and cosmetics, as base materials for packaging materials and gas barrier materials, as viscosity modifiers and dispersion stabilizers for liquid products, as base materials for artificial leather, and for apparel applications in which synthetic fibers and cellulose fibers are used.
• porous bodies such as adsorbents, sound-absorbing materials, and heat insulating materials
• base materials for transparent materials and optical materials for electronic products as additives for foods, paints, and cosmetics
• base materials for packaging materials and gas barrier materials as viscosity modifiers and dispersion stabilizers for liquid products
• base materials for artificial leather and for apparel applications in which synthetic fibers and cellulose fibers are used.

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