JP7527434B2 - Cellulose fiber composition and method for producing same - Google Patents

Description

The present invention relates to a cellulose fiber composition and a method for producing the same. More specifically, the present invention relates to an energy-saving method that does not require strong physical grinding, a method for producing a cellulose fiber composition that is nano-sized, has a high degree of crystallinity, and causes little damage to the fiber shape, and a method for producing a chemically modified cellulose fiber composition.

Cellulose fibers (cell wall units) are aggregates of cellulose fine fibers (also called microfibrils or CNF). CNF has mechanical properties comparable to those of steel and a nanostructure with a diameter of about 2 nm to 20 nm, so it has attracted attention as a reinforcing material. However, since CNF fibers are bound together by hydrogen bonds, it is necessary to break the hydrogen bonds and separate the CNF (hereinafter also referred to as defibration). For this reason, as explained below, conventionally, mechanical defibration methods that apply strong physical forces, such as underwater mechanical defibration methods, have been known. In this method, cellulose fibers are swollen with water and nano-sized in a soft state by strong mechanical shearing using a high-pressure homogenizer or water jet. Natural cellulose microfibrils are composed of a crystalline zone and an amorphous zone, and the amorphous zone absorbs a swelling solvent such as water and becomes swollen, and when it becomes deformed by strong shearing, the resulting CNF has damage, entangles, and becomes easily caught. On the other hand, when using a powerful mechanical grinding method such as a ball mill, mechanochemical reactions specific to the solid state occur, and it becomes unavoidable that the crystalline structure of cellulose is destroyed or dissolved. As a result, the yield is low and the crystallinity of the obtained fibers may be low. Furthermore, in order to combine the obtained cellulose fibers with a hydrophobic resin, it is necessary to dehydrate the fibers after defibration and perform treatments such as surface hydrophobic modification, but when defibration is performed in water, the dehydration process requires a high amount of energy, which is also a problem.

On the other hand, in place of or in addition to the mechanical fiberization method, a technique for promoting fiberization by modifying the fiberization solvent has been developed.
For example, as a method for producing cellulose fine fibers with an esterified surface, a method is known in which cellulose is mixed with an organic solvent, an esterifying agent is added, and then an esterification reaction is carried out with strong mechanical crushing to esterify and dissociate the cellulose surface. However, a defibration solution containing an esterifying agent and an organic solvent has low permeability to cellulose, and hardly penetrates into the inside of the cellulose during the mechanical crushing process. Therefore, even in this method, chemical defibration is not performed, and the fibers are produced by a mechanical defibration method that requires strong mechanical force, so there is a possibility that the CNF will be damaged. In addition, the organic solvent and the esterifying agent are less likely to penetrate the inner part of the cellulose fiber, so the inner part of the cellulose fiber is less likely to be esterified. Therefore, it is considered that even if the fine fibers in the inner part of the cellulose fiber are defibrated by mechanical defibration, the surface modification is hardly performed.

The following Patent Document 1 describes a method for producing surface-esterified cellulose fine fibers, in which a cellulose-based material is swollen and/or partially dissolved using a mixed solvent containing an ionic liquid such as 1-butyl-3-methylimidazolium chloride and an organic solvent such as N,N-dimethylacetamide, and then acetylated with acetic anhydride. However, when using the mixed solvent containing an ionic liquid and an organic solvent as in Patent Document 1, there is a problem that the cost of recovering and reusing the ionic liquid is high. In addition, the example in Patent Document 1 describes that "2 g of filter paper (ADVANTEC FILTER PAPER) cut into 3 mm squares with scissors was placed in a 200 ml beaker, 50 mL of N,N-dimethylacetamide and 60 g of the ionic liquid 1-butyl-3-methylimidazolium chloride were added thereto, and the mixture was stirred with a magnetic stirrer at 80° C. for 30 minutes, and then treated with an Ultra-Turrax homogenizer at 13,000 rpm for 5 minutes." The degree of defibration was only confirmed at a laboratory level.
Patent Document 1 describes a conventional method for producing CNF, which involves fibrillating cellulose fiber raw materials through processes such as beating and homogenization, but in order to obtain CNF with a small fiber diameter, it is necessary to perform a thorough beating process, which results in significant damage to the fibers and reduces the strength and aspect ratio of the obtained CNF. On the other hand, if the beating process is reduced to suppress fiber damage, the obtained fibers have a large fiber diameter and a small aspect ratio, so CNF with good reinforcing properties cannot be obtained. It also describes that the production efficiency of conventional methods is poor, for example, the pre-beating method requires 7 to 15 treatments with a double disc refiner, and that pre-beaten pulp is fibrillated by grinding with a grinding wheel and then subjected to a high-pressure homogenizer process, resulting in a high-strength CNF. Although microfibrillated cellulose can be obtained, a considerable number of treatments are required, resulting in low production efficiency. A method of obtaining microfibrillated cellulose using a media-agitation grinder has also been proposed, but since a suspension of fibrous cellulose is directly fed into the grinder for grinding, there is a problem that the CNF can be damaged, as in the beating process, and the time required to produce CNF is very long, resulting in low productivity. A method has also been proposed that includes a process of hydrolysis in a hydrochloric acid solution at 120 to 130°C, followed by neutralization, washing, and grinding in a disc refiner, but although the acid treatment makes it easier to separate the CNF and allows finer fibers to be obtained, long periods of acid treatment damage the CNF and inevitably result in a decrease in physical properties.

The following Patent Document 2 describes a process for producing nanocellulose material, the process including the steps of: (a) providing a biomass feedstock containing lignocellulose; (b) fractionating the feedstock in the presence of an acid such as sulfur dioxide, a lignin solvent such as ethanol, and water to produce a cellulose-rich solid and a liquid containing hemicellulose and lignin; (c) mechanically treating the cellulose-rich solid to form cellulose fibrils and/or cellulose crystals, thereby producing a nanocellulose material having a crystallinity of at least 60%; and (d) recovering the nanocellulose material. Patent Document 2 also describes that during step (c), the cellulose-rich solid is treated with less than about 1000 kilowatt-hours of total mechanical energy per ton of the cellulose-rich solid.
Patent Document 2 describes that biomass-derived pulp can be converted to nanocellulose by mechanical treatment, and that although the process may be simple, disadvantages include high energy consumption, damage to fibers and particles due to strong mechanical treatment, and a wide distribution in fibril diameter and length; biomass-derived pulp can be converted to nanocellulose by chemical treatment, for example, pulp can be treated with 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) to produce nanocellulose, but although such techniques can reduce energy consumption and produce more uniform particle sizes compared to mechanical treatment, the process is not considered economically viable; therefore, there is a need in the art for an improved process for producing nanocellulose from biomass at reduced energy costs.
Patent document 2 describes that the major technical and economic barriers to the production of CNF are high energy consumption and high cost, and that the use of sulfur dioxide ( _SO2 ) and ethanol (or other solvent) effectively removes not only hemicellulose and lignin from biomass but also amorphous regions of cellulose, resulting in a highly crystalline cellulose product that requires minimal mechanical energy for conversion to CNF. In US Patent No. 5,393,136, a 0.65 wt % suspension of bleached pulp is made and passed up to 30 times through a Microfluidics (Westwood, Massachusetts, USA) M-1 10EH-30 microfluidization processor using a combination of interaction chambers with internal diameters of 87 μm, 200 μm, and 400 μm depending on the level of size reduction required, applying a constant pressure of up to 30 kpsi to a constant velocity product stream, where the fixed geometry microchannels of the interaction chamber accelerate the product stream to a high velocity, causing the high velocity product stream to impinge on itself and on an abrasion resistant surface (polycrystalline diamond), reducing the particle size through high shear and impact forces, and confirming an energy consumption of less than 1000 kWh/ton. This energy consumption is in terms of slurry.

The following Patent Document 3 describes a method for producing a composition comprising microfibrillated cellulose and optionally an inorganic particulate material, the method comprising the steps of microfibrillating a cellulose-containing fibrous substrate using a vertical mill or the like in the presence of grinding media such as metal particles and, optionally, in the presence of an inorganic particulate material such as calcium carbonate to obtain a composition comprising microfibrillated cellulose and, optionally, an inorganic particulate material, the energy input during the microfibrillation step being about 500 to 20,000 kWh (kWh/t) per ton of cellulose-containing fibrous substrate, for example, about 1,250 to 10,000 kWh/t or, for example, about 1,750 to 4,000 kWh/t, the composition comprising (i) about 5.0% by mass or less of cellulose fibrils having a fibril diameter of less than 10 nm, based on the total mass of the cellulose-based material in the composition; and/or (ii) about 30% by mass or less of cellulose fibrils having a fibril diameter of less than 100 nm, based on the total mass of the cellulose-based material in the composition. Such compositions contain inorganic fillers that can be used in papermaking or paper coating.

The following Patent Document 4 describes a low-energy method for preparing underivatized nanocellulose material, which includes the steps of (a) treating a cellulosic material with a swelling agent such as morpholine to obtain a swollen cellulosic material, (b) subjecting the swollen cellulosic material to an effective mechanical comminution process such as high shear force, high pressure homogenization, microfluidization, high friction force, and combinations thereof, and (c) isolating the nanocellulose material. In Patent Document 4, the low-energy process refers to a process characterized by a significant reduction in the energy consumption of the mechanical processing equipment used compared to the energy-intensive prior art processes known in the art, and is defined as any efficient mechanical comminution process that can crush (or break) into small particles, usually less than 2000 kWh/t, preferably less than 1500 kWh/t, and more preferably less than 500 kWh/t. However, Patent Document 4 describes that the mechanical milling process can be carried out using conventional techniques known in the art, such as high shear force, microfluidization (e.g., M110-EH microfluidizer with two chambers attached in series), high pressure homogenizer (e.g., NanoDeBee high pressure homogenizer (BEE International Inc.), ConCor high pressure/high shear homogenizer (Primary Dispersions Ltd.)), controlled hydrodynamic cavitation (e.g., Arisdyne Systems controlled hydrodynamic cavitation device), and high friction force (e.g., Super MassColloider colloid/friction mill (Masuko)), and combinations thereof, and in the examples, the M110-EH microfluidizer is used.

The following Patent Document 5 describes a method for producing cellulose fine fibers that are nano-sized, have a high degree of crystallinity, and have little damage to the fiber shape, by permeating cellulose with a defibrating solution containing an aprotic solvent and a vinyl carboxylate or an aldehyde without mechanically crushing the cellulose. Patent Document 5 considers that defibration is caused by the defibrating solution permeating into the cellulose and breaking the hydrogen bonds between the cellulose fibers, lamellae, and microfibrils, and that the higher the donor number or electrical conductivity of the defibrating solution, the larger the void volume between the cellulose fibers, lamellae, and microfibrils caused by swelling, and the higher the degree of defibration. In addition, when the defibrating solution contains a vinyl carboxylate or an aldehyde, the vinyl carboxylate reacts with the hydroxyl groups of cellulose or the water contained in cellulose to produce acetaldehyde as a by-product, or the aldehyde forms a hemiacetal or acetal with some of the hydroxyl groups on the surface of the microfibrils, cutting the hydrogen bonds between the microfibrils, so that the microfibrils easily separate and are defibrated, and when the defibrating solution further contains a modifying reactant, the hemiacetal or acetal is unstable and is attacked by the modifying reactant to return to acetaldehyde, thereby modifying the hydroxyl groups of cellulose. In other words, the defibrating solution described in Cited Document 5 contains a vinyl carboxylate such as vinyl acetate or an aldehyde as an essential component. Patent Document 5 describes that dimethyl sulfoxide (DMSO) is preferred as an aprotic solvent from the viewpoint of the permeability of the defibrating solution, but describes that defibration did not proceed in a defibrating solution that did not contain vinyl acetate (lauroyl chloride:DMSO = 1:9) or an aldehyde-free defibrating solution (DMSO 100%). In Patent Document 5, 1 g of vinyl acetate and 9 g of DMSO are placed in a 20 ml sample bottle, stirred with a magnetic stirrer until the mixture is uniformly mixed, then 0.3 g of cellulose pulp is added, stirred for another 3 hours, and washed with distilled water to remove the defibrating solution (vinyl acetate and DMSO) and by-products (acetaldehyde or acetic acid), and the obtained cellulose fine fibers are confirmed to be modified or not by FT-IR analysis, the shape is observed with a scanning electron microscope (SEM), the crystallinity is measured by XRD analysis, and the degree of defibration and solvent dispersibility are evaluated, and defibration is only confirmed at the laboratory level. The power consumption of this stirrer is calculated as 150 kWh/kg, since 0.3 g of pulp is treated for 3 hours at 15 W.

The following Patent Document 6 describes a method for producing derivatized CNF, which is characterized by adding an organic acid vinyl such as vinyl acetate to a solution in which hydrous CNF is dispersed in a hydrophilic organic solvent such as DMSO, forming a precipitate in the reaction solution after the reaction is completed, and recovering and drying the precipitate. That is, Patent Document 6 discloses that CNF can be esterified even if it contains water by using a vinyl ester. However, the "hydrous CNF" described in Patent Document 6 is obtained by colliding high-pressure water of about 50 to 400 MPa with a polysaccharide mixed solution of 0.5 to 10 mass% water, and only discloses a technology for derivatizing already defibrated CNF. Therefore, Patent Document 6 does not disclose any method for producing cellulose fine fibers that are nano-sized, have a high degree of crystallinity, and have little damage to the fiber shape, using an energy-saving method that does not require strong physical crushing.

JP 2010-104768 A Special Publication No. 2016-501937 Special table 2016-505727 publication Special Publication No. 2015-522097 International Publication No. 2017/159823 International Publication No. 2016/010016

In view of the above-mentioned conventional techniques, the problem that the present invention aims to solve is to provide a method for producing a cellulose fiber composition that is nano-sized, has a high degree of crystallinity, and has minimal damage to the fiber shape, using an energy-saving method that does not require strong physical grinding, and a method for producing a chemically modified cellulose fiber composition.

As a result of intensive research and repeated experiments to solve the above problems, the inventors unexpectedly discovered that by using an apparatus equipped with at least a first means for supplying the contents, a second means having a rotating element capable of generating a shear force and an ejection pressure on the contents from the first means, and a third means for returning the contents from the second means to the first means, and defibrating the cellulose fibers in a specific defibrating solvent under mild conditions without mechanically crushing them, it is possible to defibrate the cellulose fibers with extremely low power consumption and produce a cellulose fiber composition that is nano-sized, has a high degree of crystallinity, and has little damage to the fiber shape, and thus completed the present invention.

That is, the present invention is as follows.
[1] the steps of:
providing an apparatus comprising at least a first means for supplying contents, a second means having a rotating element capable of producing a shear force and an ejection pressure on the contents from the first means, and a third means capable of returning the contents from the second means to the first means;
a step of feeding a cellulose-containing pulp and a defibrating solvent into the first means; and a defibrating step of rotating a rotating element of the second means at a peripheral speed of 20 m/s to 80 m/s to defibrate the cellulose by shear force to form cellulose fibers having an average fiber diameter of 2 nm to 800 nm.
A method for producing a cellulose fiber composition comprising the steps of:
[2] The method according to [1], wherein the defibration in the defibration step is performed at 20°C to 90°C for 0.5 hours to 8 hours.
[3] the steps of:
providing an apparatus comprising at least a first means for supplying contents, a second means having a rotating element capable of producing a shear force and an ejection pressure on the contents from the first means, and a third means capable of returning the contents from the second means to the first means;
introducing a cellulose-containing pulp and a defibrating solvent into the first means;
a defibration step in which the rotating element of the second means is rotated at a peripheral speed of 20 m/s to 80 m/s, and defibration is performed by shear force to form cellulose fibers having an average fiber diameter of 2 nm to 800 nm; and a chemical modification step in which a chemical modifier and a catalyst are then introduced into the first means, and the peripheral speed of the rotating element of the second means is reduced to less than 20 m/s to form chemically modified cellulose fibers having an average fiber diameter of 2 nm to 800 nm;
A method for producing a chemically modified cellulose fiber composition comprising the steps of:
[4] The method according to [3], wherein the defibration step is carried out at 20°C to 90°C for 0.5 hours to 8 hours, and the chemical modification step is carried out at 20°C to 80°C for 0.25 hours to 6 hours.
[5] the steps of:
providing an apparatus comprising at least a first means for supplying contents, a second means having a rotating element capable of producing a shear force and an ejection pressure on the contents from the first means, and a third means capable of returning the contents from the second means to the first means;
a step of feeding a cellulose-containing pulp, a defibrating solvent, a chemical modifier, and a catalyst into the first means, in which the chemical modifier and the catalyst are fed simultaneously with the feeding of the pulp or after a predetermined time has elapsed; and a defibrating/chemically modifying step of rotating a rotating element of the second means at a peripheral speed of 20 m/s to 80 m/s to defibrate the cellulose by shear force to form chemically modified cellulose fibers having an average fiber diameter of 2 nm to 800 nm;
A method for producing a chemically modified cellulose fiber composition comprising the steps of:
[6] The method according to [5], wherein the defibration and chemical modification process is carried out at 20°C to 90°C for 0.5 hours to 8 hours.
[7] The method according to any one of [1] to [6] above, wherein the first means is an agitator having a scraper capable of scraping off the contents along the inner wall surface, the second means is a rotary homogenizer disposed below the agitator, and the third means is a mixer tank or a circulation line of the tank capable of returning the product discharged from the rotary homogenizer to the agitator.
[8] The method according to any one of [1] to [7], wherein the defibrating solvent is an aprotic polar solvent which may contain up to 30% by weight of water.
[9] The method according to any one of [1] to [8], wherein the pulp is added in an amount of 1 to 10 parts by mass, calculated as a cellulose solid content, per 100 parts by weight of the defibrating solvent.
[10] The method according to [8] or [9], wherein the aprotic polar solvent is at least one selected from the group consisting of dimethylsulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and any mixture thereof.
[11] The method according to any one of [2] to [10] above, wherein the chemical modifying agent is a vinyl carboxylate.
[12] The method according to [1], wherein the carboxylic acid vinyl ester is vinyl acetate, and the chemically modified cellulose fiber is an acetylated cellulose fiber having an average degree of substitution of 0.05 to 1.2.
[13] The method according to any one of [2] to [12] above, wherein the catalyst is an alkali metal or alkaline earth metal carbonate or hydrogen carbonate.
[14] The method according to [3], wherein the catalyst is sodium bicarbonate (baking soda) or potassium carbonate.
[15] A method for producing a plastic aqueous composition of cellulose fibers or chemically modified cellulose fibers, further comprising the steps of washing the cellulose fiber composition or chemically modified cellulose fiber composition produced by the method according to any one of [1] to [14] above with water to remove most of the defibration solvent, and then dehydrating the composition under pressure to obtain a plastic aqueous composition having a solid content of 5 to 20% by weight.
[16] A method for producing a resin composite, comprising a step of melting and kneading a plastic aqueous composition of chemically modified cellulose fibers produced by the method according to [15] above with a thermoplastic resin.

According to the present invention, instead of using a powerful mechanical fiberization method using a high-pressure homogenizer or water jet, a specific device is used that includes at least a first means for supplying the contents, a second means having a rotating element capable of generating shear force and ejection pressure on the contents from the first means, and a third means for returning the contents from the second means to the first means, and the fiber is defibrated in a specific fiberization solvent under mild conditions, thereby enabling the cellulose fibers to be defibrated with extremely low power consumption, and a cellulose fiber composition having a nano-sized fiber with high crystallinity and little damage to the fiber shape to be produced. In addition, when the fiberization has progressed to a certain extent, the CNF can be chemically modified using the same device, and the obtained chemically modified CNF composition is washed with water to remove most of the fiberization solvent, and then dehydrated under pressure to obtain a paper clay-like plastic aqueous composition with a high solid content of about 20% by weight, which can be melted and kneaded with a thermoplastic resin to produce a resin composite. In other words, the present invention is an extremely useful technology in industry as a technology that enables low-cost, large-scale production of CNF-reinforced composite materials.

FIG. 1 is a schematic diagram of the apparatus. FIG. 2 is a schematic diagram of a stirrer. FIG. 2 is a schematic diagram of a rotating element. 1 is a graph of the performance curve of a homogenizing mixer. 1 is a graph showing the relationship between the peripheral speed and the flow rate of a homogenizing mixer. 1 is a graph showing the relationship between the number of passes during defibration and the average fiber diameter and crystallinity. The number of passes is a value roughly calculated by the theoretical flow rate of the homogenizing mixer (L/min) × processing time (min) / charge amount (L). 1 is a graph showing the change in degree of substitution (DS) over time in acetylation.

Hereinafter, an embodiment of the present invention will be described in detail.
The method for producing a cellulose fiber composition of the present embodiment includes the following steps:
providing an apparatus comprising at least a first means for supplying contents, a second means having a rotating element capable of producing a shear force and an ejection pressure on the contents from the first means, and a third means capable of returning the contents from the second means to the first means;
a step of feeding a cellulose-containing pulp and a defibrating solvent into the first means; and a defibrating step of rotating a rotating element of the second means at a peripheral speed of 20 m/s to 80 m/s to defibrate the cellulose by shear force to form cellulose fibers having an average fiber diameter of 2 nm to 800 nm.
The defibration in the defibration step is preferably carried out at 20° C. to 90° C. for 0.5 hours to 8 hours.

<Defibrillation of cellulose>
In the defibration step in the method for producing a cellulose fiber composition of this embodiment, a specific defibration solvent is permeated into the cellulose fibers to defibrate the cellulose fibers. When the specific defibration solvent permeates the cellulose fibers, the cellulose fibers are swelled while the hydrogen bonds between the microfibrils are broken, and the microfibrils are defibrated by themselves to obtain defibrated CNF. In this defibration step, there is no need to use a powerful defibration device such as a high-pressure homogenizer or water jet of the conventional technology, and cellulose is defibrated without relying on powerful mechanical defibration or crushing, and nano-sized CNF with high crystallinity and little damage to the fiber shape is obtained. The equipment used in this defibration step will be described later.

Because such a specific defibration solvent does not penetrate into the crystalline zone (domain) of the microfibrils, the resulting cellulose fine fibers are less damaged and have a structure close to that of natural microfibrils. At the same time, in the method for producing a cellulose fiber composition of this embodiment, the cellulose fibers can be defibrated without using mechanical defibration means that rely on the action of strong shear forces, so the resulting cellulose fibers are less damaged by physical actions. Therefore, it is believed that the resulting cellulose fibers and chemically modified cellulose fibers retain high strength.

The specific defibration solvent may be an aprotic polar solvent that may contain water, and such aprotic polar solvent is preferably at least one selected from the group consisting of dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and any mixture thereof, and is most preferably DMSO.
DMSO can be mixed with water in any ratio. As the ratio of water to the defibrating solvent increases, fiber cutting tends to occur more than defibration. In other words, by adjusting the ratio of water, it is possible to achieve an optimal balance between defibration and fiber cutting. However, if the ratio of water in the defibrating solvent is too high, the fiber shape will be severely damaged, so the ratio of water in the defibrating solvent is preferably up to 30% by weight. It is preferable to add 1 to 10 parts by mass of raw pulp in terms of cellulose solids per 100 parts by weight of the defibrating solvent.
In addition, although it depends on the equipment used in the defibration step described below, the concentration of the raw pulp/DMSO slurry is limited to 10% by weight from the standpoint of slurry viscosity and equipment clogging.

The defibration step in the method for producing a CNF composition of this embodiment includes permeating a defibration solvent into cellulose fibers to defibrate them. The reason why the cellulose fibers are defibrated by the defibration solvent is believed to be as follows.
Defibration occurs when the defibration solvent penetrates into the cellulose and breaks the hydrogen bonds between cellulose fibers, lamellae, and microfibrils. The higher the donor number or electrical conductivity of the defibration solvent, the larger the void volume between cellulose fibers, lamellae, and microfibrils caused by swelling, and the higher the degree of defibration.
When the defibrating solvent contains a vinyl carboxylate, the vinyl carboxylate reacts with the hydroxyl groups of cellulose or the water contained in cellulose to produce acetaldehyde as a by-product. This acetaldehyde forms hemiacetal or acetal with some of the hydroxyl groups on the surface of the microfibrils, and breaks the hydrogen bonds between the microfibrils. As a result, the microfibrils are easily separated from each other and defibrated. In addition, when the defibrating solvent contains a chemical modifier, the hemiacetal or acetal is unstable and is attacked by the chemical modifier to return to acetaldehyde, modifying the hydroxyl groups of the cellulose.

The cellulose fibers subjected to the defibration process may be in the form of cellulose alone, or may be in a mixed form containing non-cellulose components such as lignin and hemicellulose. The cellulose is preferably cellulose containing a crystalline cellulose structure I, and examples thereof include wood-derived pulp, wood, bamboo, linter pulp, cotton, and substances containing cellulose powder. The weight ratio of cellulose to the defibration solvent is preferably cellulose/defibration solvent = 1.0:100 to 10:100, more preferably 3:100 to 8:100, and even more preferably 4:100 to 6:100. If the cellulose ratio is too low, the production efficiency of CNF may be reduced. If the cellulose ratio is too high, the penetration of the defibration solvent between cellulose fibers, lamellae, and microfibrils may be insufficient, and the degree of defibration may decrease. In addition, the high viscosity increases the defibration time. In any case, productivity may decrease. Furthermore, when producing chemically modified CNF, if the proportion of cellulose is too high, the uniformity of the size and chemical modification rate of the resulting CNF may decrease.

Since the defibrating solvent has high permeability to cellulose, by adding cellulose to the defibrating solvent and mixing, the defibrating solvent penetrates between the microfibrils and breaks the hydrogen bonds between the microfibrils, thereby defibrating the cellulose. Furthermore, by using a chemical modifier and/or a catalyst in combination, the surface of the cellulose fibers can be modified. The rotating element of the second means of the device is rotated at a peripheral speed of 20 m/s to 80 m/s, and defibrated by shear force for 0.5 to 8 hours at 20°C to 90°C, to form cellulose fibers with an average fiber diameter of 2 nm to 800 nm. As described below, when chemical modification is performed after the defibrating process, a chemical modifier and a catalyst are added to the first means of the device, the peripheral speed of the second means is reduced to less than 20 m/s, and a chemical modification process is subsequently performed to form chemically modified cellulose fibers with an average fiber diameter of 2 nm to 800 nm, preferably at 20°C to 80°C for 0.25 to 6 hours. Furthermore, when defibration and chemical modification are carried out simultaneously or semi-sequentially, the chemical modifier and the catalyst are added simultaneously with the addition of the pulp or after a predetermined time has elapsed, and then the rotating element of the second means is rotated at a peripheral speed of 20 m/s to 80 m/s, and defibration is performed by shear force, preferably at 20°C to 90°C for 0.5 hours to 8 hours, followed by the defibration and chemical modification process to form chemically modified cellulose fibers with an average fiber diameter of 2 nm to 800 nm.

<Apparatus>
The apparatus that can be used in the method for producing a cellulose fiber composition or a chemically modified cellulose fiber composition of this embodiment is an apparatus that includes at least 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 a third means capable of returning the contents from the second means to the first means. The first means is preferably a means capable of stirring the contents to generate a turbulent flow and supplying the contents to the second means. The CNF composition is a fluid that exhibits thixotropy, and exhibits a so-called thixotropic property in which the viscosity decreases when a certain force is applied continuously, and the decreased viscosity returns to the original state when left for a certain period of time. In addition, if the rotation speed of the rotating element of the CNF composition is too high, the air is entrained and the flow rate decreases, and on the other hand, if the rotation speed is not set to a number greater than the number at which shear force is applied, the slurry does not flow and the flow rate does not increase. Therefore, it is necessary to adjust the peripheral speed to a specific range in the second means having a rotating element capable of generating a shear force and a protruding pressure on the contents from the first means, which can stir the retained contents to generate a turbulent flow and supply downstream. By using such an apparatus, when the specific defibrating solvent contains 1 to 10 parts by mass of cellulose, calculated as cellulose solids content, per 100 parts by mass of the above-mentioned solvent, for example, when a homomixer with a tank capacity of 35 L or more is used, sufficient defibration can be achieved with extremely low energy, with a rated power consumption of 0.5 to 80 kWh per kg of cellulose dry solids. In other words, the method for producing a cellulose fiber composition or a chemically modified cellulose fiber composition of this embodiment is an extremely useful method that enables the production of a CNF composition or a chemically modified CNF composition with low energy in large-scale production, rather than in a laboratory scale.

Such a device is not particularly limited, and may be, for example, a homogenizing mixer (also referred to as homomixer in this specification) as shown in Figure 1. In Figure 1, reference numeral 1 denotes an agitator (agitation propeller) having a special shape, which generates a vertical turbulent flow toward the bottom of the tank and transfers the product (contents) to a homogenizer attached to the bottom of the tank. Reference numeral 2 denotes an ultra-high speed homogenizer (rotor/stator type) with a maximum peripheral speed of 31 m/sec attached to the bottom of the tank, for example, for shearing, and the product is pulverized and dispersed to a sub-micron level by the shear force and energy such as collision between solids. Reference numeral 3 denotes a recirculation pipe that sends the homogenized product to the upper or middle stage of the tank.
An example of the agitator is shown in Figure 2. The agitator shown in Figure 2 is a movable scraper that is not fixed and does not use screws. It is machined one by one to fit the shape of the handmade tank, and fits closely to the wall of the tank, scraping off the material and improving the mixing and heat transfer efficiency.
FIG. 3 shows an example of a rotating element of the homogenizer of the homomixer (also called a rotary homomixer).
The homogenizer may be of various sizes. For example, in a type having a tank size of 35 L, the homogenizer rotor (rotating element) size is 92 mm, the motor capacity is 7.5 kW (when the voltage is 400 V), and the agitator motor capacity is 1.5 kW (when the voltage is 400 V).
Figure 4 shows an example of the relationship between the peripheral speed (m/s) of the rotating element of the homogenizer, the flow rate (water) ( ^m3 /hr), the current (A), the shear force (kW), and the discharge pressure (bar). As can be seen from Figure 4, the flow rate increases in proportion to the rotation speed (peripheral speed) of the homogenizer, and the shear force rises at a boundary of 15 to 20 m/s (at rotation speeds below this, only the pump effect occurs). The relationship shown in Figure 4 can remain basically unchanged even if the size of the homogenizer is increased. In other words, the size of the homogenizer can be designed to match the peripheral speed.

When the homomixer is used as the device, the first means is an agitator having a scraper that can scrape off the contents along the inner wall surface, the second means is a rotary homomixer arranged under the agitator, and the third means can correspond to a circulation line that can return the discharged material of the rotary homomixer to the agitator. As long as the same function is performed in the tank, the circulation line is not necessarily required. By arranging the second means under the first means, sending the contents to the second means by the first means, returning the contents to the first means via the third means by the discharge pressure of the second means, and stirring the contents returned by the first means, cellulose can be defibrated by shear force very efficiently. In addition, by monitoring the peripheral speed of the rotating element of the second means and the flow rate in the third means, the operation and management of the defibration process can be facilitated.

In the defibration step in the method for producing a cellulose fiber composition of this embodiment, the rotating element of the second means is rotated at a peripheral speed of 20 m/s to 80 m/s, and defibration is performed by shear force, preferably at 20° C. to 90° C. for 0.5 to 8 hours, to form cellulose fibers with an average fiber diameter of 2 nm to 800 nm. In the chemical modification step following the defibration step in the method for producing a chemically modified cellulose fiber composition of this embodiment, a chemical modifier and a catalyst are introduced into the first means of the device, the peripheral speed of the rotating element of the second means is reduced to less than 20 m/s, and chemically modified cellulose fibers with an average fiber diameter of 2 nm to 800 nm can be formed, preferably at 20° C. to 80° C. for 0.25 to 6 hours. If the peripheral speed of the rotating element is less than 20 m/s, the shear force in the second means is insufficient, and defibration does not proceed. On the other hand, if the speed exceeds 50 m/s, air will be entrapped due to the thixotropy of the CNF composition, making it impossible to secure the discharge pressure and enabling recirculation, and there is also a risk of the decomposition of the CNF progressing.
Furthermore, in the defibration/chemical modification step in which the defibration step and the chemical modification step are carried out simultaneously in the production method of a chemically modified cellulose fiber composition of this embodiment, the rotating element of the second means is rotated at a peripheral speed of 20 m/s to 80 m/s, and defibration is performed by shear force, preferably at 20° C. to 90° C. for 0.5 hours to 8 hours, to form chemically modified cellulose fibers with an average fiber diameter of 2 nm to 800 nm. In other words, by using the above-mentioned device, it is possible to produce a chemically modified cellulose fiber composition on a large scale with low energy by appropriately changing the operating conditions of the same device for the chemical modification step subsequent to the defibration step.

<Chemical modification>
Other embodiments of the present invention can be the following sequential method, in which defibration is followed by chemical modification, or simultaneous or semi-sequential method, in which defibration and chemical modification are performed simultaneously or stepwise.
<Sequential method>
The following steps:
providing an apparatus comprising at least a first means for supplying contents, a second means having a rotating element capable of producing a shear force and an ejection pressure on the contents from the first means, and a third means capable of returning the contents from the second means to the first means;
introducing a cellulose-containing pulp and a defibrating solvent into the first means;
a defibration step in which the rotating element of the second means is rotated at a peripheral speed of 20 m/s to 80 m/s, and defibration is performed by shear force to form cellulose fibers having an average fiber diameter of 2 nm to 800 nm; and a chemical modification step in which a chemical modifier and a catalyst are then introduced into the first means, and the peripheral speed of the rotating element of the second means is reduced to less than 20 m/s to form chemically modified cellulose fibers having an average fiber diameter of 2 nm to 800 nm;
The defibration step is preferably carried out at 20°C to 90°C for 0.5 to 8 hours, and the chemical modification step is preferably carried out at 20°C to 80°C for 0.25 to 6 hours.
<Simultaneous method, semi-sequential method>
The following steps:
providing an apparatus comprising at least a first means for supplying contents, a second means having a rotating element capable of producing a shear force and an ejection pressure on the contents from the first means, and a third means capable of returning the contents from the second means to the first means;
a step of feeding a cellulose-containing pulp, a defibrating solvent, a chemical modifier, and a catalyst into the first means, in which the chemical modifier and the catalyst are fed simultaneously with the feeding of the pulp or after a predetermined time has elapsed; and a defibrating/chemically modifying step of rotating a rotating element of the second means at a peripheral speed of 20 m/s to 80 m/s to defibrate the cellulose by shear force to form chemically modified cellulose fibers having an average fiber diameter of 2 nm to 800 nm;
The defibration and chemical modification step can be preferably carried out at a temperature of 20° C. to 90° C. for 0.5 hours to 8 hours.

<Addition of chemical modifiers and catalysts>
When a chemical modifier is added to the defibrating solvent, it can be mixed by stirring or the like and dissolved uniformly. The order of mixing may be all added at the same time, or they may be added sequentially while stirring and mixed. When a chemical modifier with low polarity is used, the penetration rate of the defibrating solvent, the swelling rate of the cellulose fibers, and the defibrating rate may decrease. Therefore, it is preferable to permeate the defibrating solvent containing no chemical modifier into the cellulose fibers, and add the chemical modifier to the defibrating solvent when defibration has progressed to a certain extent.
When a catalyst is added to the defibrating solvent, it can be mixed by stirring or the like and dissolved or suspended uniformly. The addition of a catalyst can improve the polarity of the defibrating solvent and further promote defibration. The chemical modifier and catalyst may be added simultaneously, or may be added successively while stirring and mixed. Usually, a method is used in which pulp, chemical modifier, and catalyst are added successively to the defibrating solvent. The catalyst may also be added when defibration has progressed to a certain extent by permeating a defibrating solvent not containing a catalyst into the cellulose fibers. When the chemical modifier and/or catalyst are added after permeating the defibrating solvent into the cellulose fibers, they may be added directly to the defibrating solvent, or may be added after dissolving them in any suitable solvent. The any suitable solvent may be a solvent used as the defibrating solvent.

The chemical modifying agent is preferably a vinyl carboxylate.
When vinyl acetate is used as the chemical modifying agent, acetylated cellulose having an average degree of substitution of 0.05 to 1.2 can be obtained.

The content of the vinyl carboxylate in the defibrating solvent is preferably 0.05% to 50% by weight, more preferably 1% to 40% by weight, and even more preferably 2% to 30% by weight, based on the total amount of the defibrating solvent. If the content of the vinyl carboxylate is less than 0.05% by weight, the rate of chemical modification may be insufficient. On the other hand, if the content of the vinyl carboxylate exceeds 50% by weight, the permeability of the defibrating solvent into the cellulose may decrease. By keeping the content of the vinyl carboxylate in this range, the balance between the permeability between the microfibrils and the reactivity with the hydroxyl groups of the cellulose is improved.

Vinyl carboxylate esters are not particularly limited, and examples thereof include 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. These compounds may be used alone or in combination of two or more. Vinyl acetate is preferred.

The defibrating solvent may further contain a base catalyst or an acid catalyst depending on the type of chemical modifier. By including a catalyst in the defibrating solvent, the chemical modification reaction is promoted and the polarity of the defibrating solvent is improved, further promoting defibration. Base catalysts and acid catalysts have high dielectric constants, and adding them increases the dielectric constant of the defibrating solvent. As a result, the affinity of the defibrating solvent for cellulose increases, and the penetration rate and swelling rate of the defibrating solvent improve. Furthermore, it promotes the dissolution of non-crystalline components such as soluble hemicellulose contained in cellulose, and has the effect of accelerating the defibration of microfibrils.

As described above, when the defibrating solvent contains a vinyl carboxylate, by further adding a catalyst to the defibrating solvent, the cellulose is defibrated and the vinyl carboxylate undergoes an ester exchange reaction with the hydroxyl groups of the cellulose, thereby obtaining esterified chemically modified CNF. The catalyst may be either an acid catalyst or a base catalyst. The content of the base catalyst or acid catalyst relative to the entire defibrating solvent is preferably 0.001% by weight to 0.5% by weight.
When using a base catalyst, if the base catalyst is too alkaline, the defibrating solvent may penetrate into the crystals, which may reduce the crystallinity of the CNF. Therefore, any appropriate base catalyst that does not destroy the crystal structure of cellulose can be used as the base catalyst. As the base catalyst, preferred are carboxylates such as carbonates, hydrogen carbonates, and acetates; borates; phosphates; hydrogen phosphates; salts of alkali metals or alkaline earth metals such as tetraalkylammonium acetates; pyridines, imidazoles, and amines. The base catalyst is more preferably a carbonate or hydrogen carbonate of an alkali metal or alkaline earth metal, and even more preferably sodium hydrogen carbonate (sodium bicarbonate). By containing these base catalysts, the polarity (dielectric constant) of the defibrating solvent is increased, and the permeation rate is improved, which is preferable. A strongly basic (strongly alkaline) catalyst may reduce the stability of cellulose. Therefore, when a strongly basic catalyst is used, it is preferable that the content of the base catalyst in the defibrating solvent is 0.1% by weight or less. The base catalyst may be used alone or in combination of two or more kinds.

In the chemical modification process and the defibration and chemical modification process, it is preferable to carry out the process in a closed or pressurized system to prevent the evaporation of the vinyl carboxylate. Furthermore, it is preferable to apply pressure to prevent the evaporation of the low-boiling component of acetaldehyde, which is a by-product of the vinyl carboxylate.

<Separation and purification>
The cellulose fibers or chemically modified cellulose fiber composition obtained by defibration may be separated and purified by any appropriate method. Examples of the separation and purification method include centrifugation, filtration, concentration, and precipitation. For example, the defibration mixture (defibration solution containing defibrated cellulose) may be centrifuged or filtered to separate the cellulose fine fibers and the defibration solvent. Alternatively, a solvent capable of dissolving the catalyst and the defibration solvent (water, alcohols, ketones, etc.) may be added to the defibration mixture, and separation and purification (washing) may be performed by a separation method (any appropriate method) such as centrifugation, filtration, and precipitation. The separation operation may be performed multiple times (for example, about 2 to 5 times). When a chemical modifier is added, the chemical modifier may be deactivated with water or methanol after the reaction is completed, or may be recovered by distillation without being deactivated from the viewpoint of reuse.
A paper-like plastic aqueous composition of cellulose fibers or chemically modified cellulose fibers can be produced by washing the cellulose fiber composition or chemically modified cellulose fiber composition obtained in the defibration step, or chemical modification step, with water to remove most of the defibration solvent, and then applying pressure to dehydrate the composition to obtain a plastic aqueous composition with a solid content of 5 to 20% by weight. A resin composite can be produced by melting and kneading the plastic aqueous composition of chemically modified cellulose fibers thus obtained with a thermoplastic resin.
A filter dryer (pressure filtration device) can be used when "washing with water to remove most of the defibrating solvent, and then applying pressure to dehydrate" as described above. The solids concentration in the cellulose fiber or chemically modified cellulose fiber composition is up to about 30%, and at this point the composition is in a clay-like or bean curd refuse-like state. If the solids concentration is concentrated to nearly 30% by weight, it becomes difficult to redisperse the composition when it is diluted with water again. For this reason, the solids content in the cellulose fiber or chemically modified cellulose fiber composition is preferably 5 to 20% by weight.

The average fiber diameter of the CNF in the paper-like plastic aqueous composition of cellulose fibers or chemically modified cellulose fibers can be 2 nm to 800 nm, and the aspect ratio can be 40 to 1000. The obtained CNF is defibrated to nano-size or submicrometer, and the average fiber diameter is, for example, preferably 3 nm to 600 nm, more preferably 5 nm to 500 nm, and even more preferably 10 nm to 300 nm. If the fiber diameter is too large, the effect as a reinforcing material may decrease. If the fiber diameter is too small, the handleability and heat resistance of the fine fibers may also decrease.
The obtained CNF has a longer fiber length than the fine fibers obtained by the conventional mechanical fiber defibration method because no strong mechanical shear force is applied, and the average fiber length is, for example, 1 μm or more. The obtained CNF has an average fiber length in the range of, for example, about 1 μm to 200 μm, but the reaction conditions can be controlled according to the application to obtain cellulose fine fibers with an appropriate average fiber length. In general, the average fiber length is, for example, 1 μm to 100 μm, preferably 2 μm to 60 μm, and more preferably 3 μm to 50 μm. If the fiber length is too short, the reinforcing effect may decrease. Also, if the fiber length is too long, the fibers may easily become entangled, and the dispersibility in solvents and resins may decrease.
The aspect ratio of CNF can be easily controlled by the composition of the defibration solvent and the infiltration time. In general, the aspect ratio is 40 to 1000. From the viewpoint of dispersibility and reinforcing effect, the aspect ratio is more preferably 50 to 800, and even more preferably 80 to 600. An aspect ratio of less than 40 is not preferred because although it is easy to disperse, the reinforcing effect and the strength of the free-standing film are low. On the other hand, an aspect ratio of more than 1000 may cause a decrease in dispersibility due to entanglement of the fibers.

The surface of the chemically modified cellulose fiber of this embodiment is uniformly modified, so it can be well dispersed in organic solvents and resins. In the manufacturing method of this embodiment, the fine fibers are modified in a defibration solvent in a stretched state, so that the hydroxyl groups on the surface are uniformly modified (uniformly), and the stretched state can be maintained even after drying. In contrast, in the conventional technology, for example, in order to prepare chemically modified CNF, cellulose is first defibrated in water by strong mechanical crushing or shearing force, and then the water is replaced with an aprotic polar solvent such as acetone or toluene, and a modification reaction is carried out. During the solvent replacement, the unmodified CNF becomes an aggregated state in which the fine fibers are bonded to each other, gathered together, or entangled with themselves, resulting in a clump of fine fibers. Even if it is placed in a reaction solvent in this state, it exists as an aggregated clump, so only the hydroxyl groups on the surface of the clump are modified, and the resulting chemically modified fine fibers cannot be well dispersed in a solvent or resin.

In order to effectively express the properties of chemically modified CNF (e.g., low linear expansion properties, strength, heat resistance, etc.) in the resin, it is preferable that the CNF has high crystallinity. In the manufacturing method of this embodiment, the raw cellulose is chemically defibrated and the crystallinity can be maintained at a high level, so the crystallinity can be maintained at the same value as the cellulose used. The crystallinity of the chemically modified cellulose fiber is, for example, 50% or more, preferably 50% to 98%, more preferably 55% to 95%, even more preferably 60% to 92%, and particularly preferably 65% to 90%. If the crystallinity is too low, there is a risk of reducing properties such as linear expansion properties and strength.

The average degree of substitution of chemically modified cellulose fibers (the average number of substituted hydroxyl groups per glucose, the basic structural unit of cellulose) can vary depending on the fine fiber diameter and the type of chemical modifier. The average degree of substitution is preferably 0.2 to 1.2, and more preferably 0.25 to 1.0. If the average degree of substitution is too high, the crystallinity or yield of the fine fibers may decrease.

The present invention will be specifically explained below based on examples, but the present invention is not limited to these examples. Details of the raw materials used are as follows, and various physical properties of the obtained cellulose fibers and chemically modified cellulose fibers were measured as follows.

<Raw material, defibration solvent, catalyst, chemical modifier>
The cellulose that is the raw material for CNF includes natural cellulose and regenerated cellulose.
As the natural cellulose, any of wood pulp obtained from broadleaf or coniferous trees and refined pulp from non-wood species (i.e., non-wood pulp) can be used. As the non-wood pulp, cotton-derived pulp including cotton linter pulp (e.g., refined linter), hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, straw-derived pulp, etc. can be used. Representative examples of cotton-derived pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp include refined pulp obtained from raw materials such as cotton lint, cotton linter, hemp-based abaca (e.g., mostly from Ecuador or the Philippines), zaisal, bagasse, kenaf, bamboo, straw, etc., through a refinement process such as delignification by cooking and a bleaching process. In addition, refined products of seaweed-derived cellulose and sea squirt cellulose can also be used. Here, lignin and hemicellulose can be mentioned as components other than cellulose remaining in the pulp, but since both of these components induce a decrease in heat resistance and the associated discoloration when composited with a resin, it is better for the content of these components in the cellulose raw material to be small. Specifically, the lignin content of the cellulose raw material is preferably 2% by mass or less, more preferably 1% by mass or less, and even more preferably 0.6% by mass or less. The hemicellulose content of the cellulose raw material is preferably 13% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.
On the other hand, regenerated cellulose is a substance obtained by dissolving or crystal swelling (mercerization) natural cellulose and regenerating it, and refers to a β-1,4-linked glucan (glucose polymer) having a molecular arrangement that gives a crystal diffraction pattern (cellulose II type crystal) with vertices at diffraction angles corresponding to lattice spacings of 0.73 nm, 0.44 nm, and 0.40 nm by particle beam diffraction. In the X-ray diffraction pattern of cellulose II type crystal, the X-ray diffraction pattern with a 2θ range of 0° to 30° has one peak at 10°≦2θ<19° and two peaks at 19°≦2θ≦30°. Examples of regenerated cellulose include rayon, cupra, and Tencel. Since it is easy to produce fibers with a fiber diameter of more than 100 nm from regenerated cellulose, it may be preferable from the viewpoint of dispersibility. Among these, it is preferable to use fibers finely made from cupra or Tencel, which have a high molecular orientation in the fiber axis direction, from the viewpoint of ease of fineness. Furthermore, cut threads of regenerated cellulose fibers and cut threads of cellulose derivative fibers can also be used. Furthermore, natural cellulose and regenerated cellulose may be mixed and used as the raw material.
In addition, since the raw pulp is in the form of a sheet, the fibers may be loosened or cut by wet processing using a pulper, beater, refiner, etc., or by dry processing using a shredder, dry refiner, hammer mill, crusher (ATOMZ, Ishikawa Soken Co., Ltd., etc.) in order to facilitate feeding into the equipment or to suppress twisting. In addition, dry grinding generally leads to a decrease in the crystallinity of cellulose, but using ATOMZ, Ishikawa Soken Co., Ltd., is preferable because it suppresses the decrease in crystallinity.
As the defibrating solvent, products of reagent manufacturers such as Kishida Chemical Co., Ltd. and Kanto Chemical Co., Ltd., or industrial products can be used, but a solvent that has been recovered and regenerated by distillation or the like can also be used. The defibrating solvent may contain water, but since water inhibits defibration and the reaction when chemically modifying the hydroxyl groups of cellulose, the water content is preferably 50% or less, preferably 30% or less, and more preferably 10% or less.
As for catalysts and chemical modifiers, products of reagent manufacturers such as Kishida Chemical Co., Ltd. and Kanto Chemical Co., Ltd., or industrial products can be used.
In the following examples, pulp derived from cotton linters in sheet form obtained from Japan Pulp and Paper Co., Ltd. was used as the cellulose raw material, DMSO with a moisture content of 0.5% or less obtained from Kishida Chemical Co., Ltd. was used as the defibrating solvent, sodium bicarbonate obtained from Kanto Chemical Co., Ltd. was used as the catalyst, and vinyl acetate obtained from Kishida Chemical Co., Ltd. was used as the chemical modifying agent.

<Preparation of measurement sample>
First, a concentrate of the aqueous dispersion of cellulose fiber or chemically modified cellulose fiber obtained in the examples and comparative examples is obtained by centrifugation (solid content of 5% by mass or more). Then, the concentrate containing 0.5 g of cellulose fiber or chemically modified cellulose fiber is dispersed in tert-butanol so that the concentration becomes 0.2% by mass, and the concentrate is further dispersed by ultrasonic dispersion or the like until no aggregates are present. 100 g of the obtained tert-butanol dispersion is filtered on a filter paper (5C, Advantec, diameter 90 mm), and the wet paper formed on the filter paper is peeled off and dried at 150°C alone to obtain a sheet. The sheet having an air resistance of 100 sec/100 ml or less per 10 g/ ^m2 of sheet basis weight is used as a porous sheet and is used as a measurement sample.
The air resistance (sec/100 ml) per 10 g/ ^m2 sheet basis weight is measured by measuring the basis weight W (g/ ^m2 ) of a sample left to stand for one day in an environment of 23°C and 50% RH, and then measuring the air resistance R (sec/100 ml) using an Oken air resistance tester (manufactured by Asahi Seiko Co., Ltd., model EG01). The value per 10 g/ ^m2 basis weight is then calculated according to the following formula:
Air resistance per unit area of 10 g/ ^m2 (sec/100 ml) = R/W x 10

(1) Number average fiber diameter First, three randomly selected points on the surface of the porous sheet are observed with a scanning electron microscope (SEM) at a magnification of 10,000 to 100,000 times depending on the fiber diameter of the fine fibers. In each of the three SEM images obtained, lines are drawn in the horizontal and vertical directions on the screen, and the number of fibers intersecting the lines and the fiber diameter of each fiber are measured from the enlarged image, and two series of number average fiber diameters, vertical and horizontal, are calculated for each image. The number average of the number average fiber diameters for the three images is taken as the average fiber diameter of the target sample.

(2) Crystal form and crystallinity: A diffraction pattern is measured (at room temperature) by a powder method using an X-ray diffraction apparatus (Rigaku Corporation, multipurpose X-ray diffraction apparatus), and the crystallinity is calculated by the Segal method using the following formula. The crystal form is also measured from the obtained X-ray diffraction image.
Crystallinity (%) = [I ₍₂₀₀₎ - I _(amorphous) ] / I ₍₂₀₀₎ x 100
{In the formula, I ₍₂₀₀₎ is the diffraction peak intensity due to the 200 plane (2θ=22.5°) in cellulose I type crystals, and I _(amorphous) is the halo peak intensity due to the amorphous phase in cellulose I type crystals, which is the peak intensity at an angle 4.5° lower (2θ=18.0°) than the diffraction angle of the 200 plane.}
<X-ray diffraction measurement conditions>
Equipment: MiniFlex (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.

(3) Evaluation of the degree of chemical modification (DS average degree of substitution)
The degree of chemical modification of the cellulose fibers is evaluated by drying the cellulose fibers to form a porous sheet, and then measuring the infrared spectrum of the porous sheet by the ATR-IR method using a Fourier transform infrared spectrophotometer (FT/IR-6200 manufactured by JASCO Corporation). The infrared spectrum measurement is performed under the following conditions.
(Infrared Spectroscopic Measurement 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 is calculated according to the following formula.
IR index = H1730/H1030
H1730 and H1030 are absorbances at 1730 cm ^-1 and 1030 cm ^-1 (absorption bands of C-O stretching vibration of the cellulose skeletal chain), respectively, where the lines connecting 1900 cm ^-1 and 1500 cm ^-1 and 800 cm ^-1 and 1500 cm ^-1 are taken as baselines, and these mean absorbances when these baselines are taken as absorbance 0.
Next, the average degree of substitution (DS) is calculated from the IR index according to the following formula.
DS = 4.13 x IR index

[Example 1: Only defibration]
The raw materials were charged into a KAPPA VITA (registered trademark) homomixer (tank size 35 L) in the amounts shown in Table 1 below, and the fiberization process was carried out.

The circulation amount of the CNF/DMSO slurry (flow rate in the circulation line) was evaluated using an ultrasonic flowmeter. The results are shown in Table 2 below. For reference, the flow rate when using water is also shown.

During defibration, the homogenizer rotation speed was set to 6000 RPM (circumferential speed: approximately 28.6 m/s). Due to the thixotropy of the CNF/DMSO slurry, the flow rate increased linearly at a peripheral speed of 15 m/s or more, where shear was applied. The slurry did not flow at a peripheral speed of 10 m/s or less, where almost no shear was applied.
FIG. 5 shows the relationship between the peripheral speed of the homogenizer and the flow rate of the CNF/DMSO slurry.
Figure 6 shows the relationship between the number of passes = {circulation amount (L/min) x time (min)}/slurry volume (L) and the average fiber diameter and crystallinity of the defibrated CNF.
It can be seen that the average fiber diameter decreases with increasing number of passes, but the crystallinity does not change.

The energy required for defibration, calculated per kg of cellulose dry solids, is shown in Table 3 below in comparison with that of conventional technology devices.
In this embodiment, sufficient defibration was achieved with extremely low energy consumption of rated power consumption of 0.5 to 80 kWh per kg of dry solid cellulose.

[Example 2: Sequential method (acetylation after defibration)]
Linter pulp and DMSO were charged in the amounts shown in Table 4 below into a KAPPA VITA (registered trademark) homomixer (tank size 35 L), and defibrated for 8 hours at a homomixer rotation speed of 6000 rpm (circumferential speed 29 m/s). Sodium bicarbonate and vinyl acetate were then added, and acetylation was carried out for 4 hours at 60° C. During acetylation, the homomixer rotation speed was set to 2500 rpm (circumferential speed 12 m/s), just before the shear force rises, in order to prevent retention in the circulation line.
The change in the degree of substitution over time is shown in Figure 7. The degree of substitution was increased to 1.0 in about 4 hours.
The average fiber diameter of the obtained chemically modified cellulose fibers was approximately the same as the average fiber diameter of the cellulose fibers obtained in Example 1, and the crystallinity was 82%.

[Example 3: Simultaneous method (simultaneous defibration and acetylation)]
The raw materials were charged in the amounts shown in Table 4 into a KAPPA VITA (registered trademark) homomixer (tank size 35 L), and defibration and chemical modification were carried out for 4 hours at 60° C. and a homomixer rotation speed of 6,000 rpm (circumferential speed 29 m/s). The average fiber diameter of the obtained chemically modified cellulose fibers was the same as that of the cellulose fibers obtained in Example 1, with a degree of substitution of 1.1 and a degree of crystallinity of 80.5%.

[Example 4]
The raw materials were charged in the amounts shown in Table 1 into a VT-1H-25 vacuum emulsification mixer with a tank size of 25 L manufactured by Mizuho Kogyo Co., Ltd., and the fiberization process was carried out for 6 hours at 5400 rpm. The energy per kg of cellulose was 41 kWh/kg, and cellulose fibers with an average fiber diameter of 41 nm and a crystallinity of 81% were obtained.

According to the method for producing a (chemically modified) cellulose fiber composition of the present invention, instead of using a powerful mechanical fiberization method using a high-pressure homogenizer or water jet, a specific device is used that has at least a first means for supplying the retained contents, a second means having a rotating element capable of generating shear force and ejection pressure on the contents from the first means, and a third means for returning the contents from the second means to the first means, and the fiber is defibrated under mild conditions in a specific fiberization solvent, thereby defibrating the cellulose fibers with extremely low power consumption and producing a cellulose fiber composition that is nano-sized, highly crystallized, and has little damage to the fiber shape. In addition, when fiberization has progressed to a certain extent, the cellulose fibers can be chemically modified using the same device, and the obtained chemically modified cellulose fiber composition is washed with water to remove most of the fiberization solvent, and then dehydrated under pressure to obtain a paper clay-like plastic aqueous composition with a high solid content of about 20% by weight, which can be melted and kneaded with a thermoplastic resin to produce a resin composite. In other words, this invention is a useful technology that enables low-cost, large-scale production of CNF-reinforced composite materials and can be widely used in a variety of industries, including the automotive industry.

1 Agitator (mixing propeller)
2. Ultra-high speed homogenizer (rotor/stator type) attached to the bottom of the tank
3 Recirculation pipe

Claims (4)

The following steps:
providing an apparatus comprising at least a first means for supplying contents, a second means having a rotating element capable of producing a shear force and an ejection pressure on the contents from the first means, and a third means capable of returning the contents from the second means to the first means;
introducing a cellulose-containing pulp and a defibrating solvent into the first means;
a defibration step of rotating the rotating element of the second means at a peripheral speed of 20 m/s to 80 m/s and defibrating the cellulose with a shear force to form cellulose fibers having an average fiber diameter of 2 nm to 800 nm; and a step of applying pressure to obtain a plastic aqueous composition having a solid content of 5 to 30% by weight;
2. A method for producing a plasticized aqueous composition of a cellulose fiber composition comprising: The manufacturing method according to claim 1, in which the defibration step is carried out at 20°C to 90°C for 0.5 hours to 8 hours. The following steps:
providing an apparatus comprising at least a first means for supplying contents, a second means having a rotating element capable of producing a shear force and an ejection pressure on the contents from the first means, and a third means capable of returning the contents from the second means to the first means;
a step of introducing a cellulose-containing pulp, a defibrating solvent, a chemical modifier, and a catalyst into the first means, wherein the chemical modifier and the catalyst are introduced simultaneously with the introduction of the cellulose-containing pulp or after a predetermined time has elapsed;
a defibration/chemical modification step of rotating the rotating element of the second means at a peripheral speed of 20 m/s to 80 m/s and defibrating the cellulose fibers by shear force to form chemically modified cellulose fibers having an average fiber diameter of 2 nm to 800 nm; and a step of washing the defibrated/chemically modified cellulose fibers with water to remove most of the defibration solvent, and then dehydrating the fibers by applying pressure to obtain a plastic aqueous composition having a solid content of 5 to 30% by weight.
A method for producing a plasticized aqueous composition of a chemically modified cellulose fiber composition comprising: A method for producing a resin composite, comprising a step of melting and kneading a cellulose fiber composition or a plastic aqueous composition of chemically modified cellulose fibers produced by the method for producing a plastic aqueous composition according to any one of claims 1 to 3 with a thermoplastic resin.

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