Method for producing acylated modified cellulose fine fibers

Abstract

To provide a production method of acylation-modified cellulose fine fiber by impregnating cellulose with a modification reaction solution, fibrillating the cellulose and simultaneously acylation-modifying the cellulose.SOLUTION: In a production method of acylation-modified cellulose fine fiber, cellulose is impregnated with a modification reaction solution containing tetraalkylammonium hydroxide represented by formula (1), water, dimethyl sulfoxide and an acylating agent so that the cellulose is acylation-modified and fibrillated. R4N+OH- (1). (In the formula, each of R represents independently a 2-4C alkyl group.)SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing acylated modified cellulose fine fibers. [Background technology]

[0002] The applicant has filed numerous patent applications relating to the dissolution of cellulose, defibrillation of cellulose into Celnose nanofibers (cellulose fine fibers), and methods for producing the same. Representative patent applications related to the present application are listed below.

[0003] In Patent Document 1, which dissolves cellulose to produce modified cellulose, cellulose is dissolved in tetraalkylammonium acetate and an aprotic polar solvent, and then the cellulose is subjected to esterification and etherification reactions to produce modified cellulose.

[0004] Patent Documents 2 to 4 are examples of prior art techniques for obtaining modified cellulose nanofibers by defibrating cellulose into cellulose nanofibers without dissolving it.

[0005] In Patent Document 2, cellulose is swelled and / or partially dissolved with tetraalkylammonium acetate and an aprotic polar solvent to defibrate it, and then chemically modified to produce modified cellulose nanofibers.

[0006] In Patent Document 3, modified cellulose fine fibers are produced by impregnating cellulose with a defibrating solution containing an aprotic solvent with a donor number of 26 or more and a carboxylic acid vinyl ester or an aldehyde.

[0007] Patent Document 4 discloses a method for producing a copolymer of an aprotic solvent having a donor number of 26 or more, a vinyl carboxylic acid ester, and a compound of the formula {X - (R1)(R2)(R3)N + -R4-Y (where X -Modified cellulose fine fibers are produced by impregnating cellulose with a defibrating solution containing a quaternary ammonium salt (R1 to R3 are alkyl groups, R4 is an alkylene group, and Y is OH, SH, or NH2). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5820688 [Patent Document 2] Patent No. 5875323 [Patent Document 3] International Publication No. 2017 / 159823 [Patent Document 4] Japanese Patent Publication No. 2021-116336 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides a method for producing acylated modified cellulose fine fibers, which comprises impregnating cellulose with a modification reaction solution to simultaneously finely defibrate and acylate the cellulose. [Means for solving the problem]

[0010] As a result of extensive research to achieve the above-mentioned object, the inventors have discovered a method for efficiently producing acylated modified cellulose fine fibers with excellent dispersibility in resins, by impregnating cellulose with a modification reaction solution containing tetraalkylammonium hydroxide (hereinafter sometimes abbreviated as "TAAH"), water, dimethyl sulfoxide (hereinafter sometimes abbreviated as "DMSO"), and an acylating agent without pre-treating the cellulose, thereby acylating the cellulose and micronizing it.

[0011] That is, the present invention is characterized by the following constitution and solves the above-mentioned problems. [1] A method for producing acylated modified cellulose fine fibers, comprising impregnating cellulose with a modification reaction solution containing tetraalkylammonium hydroxide represented by the following formula (1), water, dimethyl sulfoxide, and an acylating agent, to acylate-modify the cellulose and defibrate it: R4N + OH - (1) (wherein, each R independently represents an alkyl group having 2 to 4 carbon atoms). [2] A method for producing acylated modified cellulose fine fibers, comprising: impregnating cellulose with a solution containing tetraalkylammonium hydroxide represented by the following formula (1), water, and dimethyl sulfoxide to swell and / or partially decompose the cellulose; then adding an acylating agent to the solution to form a modification reaction solution; and acylating and defibrating the swollen and / or partially decomposed cellulose. R4N + OH - (1) (wherein, each R independently represents an alkyl group having 2 to 4 carbon atoms). [3] The production method according to [1] or [2], wherein the component ratios of the tetraalkylammonium hydroxide, water, methyl sulfoxide, and acylating agent in the modification reaction solution are 0.1 to 1.2 wt% of tetraalkylammonium hydroxide, 0.1 to 1.8 wt% of water, 82.0 to 98.8 wt% of dimethyl sulfoxide, and 1.0 to 15.0 wt% of the acylating agent, relative to the total amount of the tetraalkylammonium hydroxide, water, methyl sulfoxide, and acylating agent. [Effects of the Invention]

[0012] The presence of TAAH and water in the modification reaction solution of the present invention not only improves the efficiency of penetration of the modification reaction solution between cellulose fibrils, but also promotes the cleavage of hydrogen bonds and the acylation modification reaction. This dual effect allows for the production of acylated cellulose fine fibers with high uniformity and high defibration. Therefore, it is possible to efficiently produce cellulose fine fibers with high crystallinity, minimal damage to the fiber shape, a large aspect ratio, and the ability to nano-disperse in resins by melt kneading. Furthermore, various acyl groups can be introduced depending on the application, further improving affinity with organic media such as resins.

[0013] Furthermore, in the method for producing acylated modified cellulose fine fibers of the present invention, the modification reaction time or defibration time can be shortened by adding tetraalkylammonium hydroxide and water. [Brief explanation of the drawings]

[0014] [Figure 1] IR spectra of acetylated modified cellulose fine fibers obtained in Examples 1, 2, 4, 6, and 7 and Comparative Example 1 [Figure 2] SEM photograph of acetylated modified cellulose fine fibers obtained in Example 1 [Figure 3] SEM photograph of acetylated modified cellulose fine fibers obtained in Example 2 [Figure 4] SEM photograph of acetylated modified cellulose fine fibers obtained in Example 4 [Figure 5] SEM photograph of acetylated modified cellulose fine fibers obtained in Example 5 [Figure 6] SEM photograph of acetylated modified cellulose fine fibers obtained in Example 6 [Figure 7] SEM photograph of acetylated modified cellulose fine fibers obtained in Example 7 [Figure 8] SEM photograph of wood pulp treated in Comparative Example 1 DETAILED DESCRIPTION OF THE INVENTION

[0015] The method for producing cellulose fine fibers of the present invention is characterized in that, without pre-treating the cellulose by mechanical crushing or drying, a modification reaction solution containing TAAH, water, DMSO, and an acylating agent is impregnated into the cellulose to acylate the cellulose and also break the hydrogen bonds between the cellulose microfibrils, thereby weakening the interactions between the microfibrils, thereby producing acylated cellulose fine fibers.

[0016] In the method for producing cellulose fine fibers of the present invention, an acylating agent may be added after cellulose has been defibrated to a certain extent. That is, a solution containing TAAH, water, and DMSO (hereinafter referred to as "defibration solution") is impregnated into cellulose to swell and / or partially decompose the cellulose, and then an acylating agent is added to the solution to prepare a modification reaction solution, which acylates the swollen and / or partially decomposed cellulose and breaks the hydrogen bonds between cellulose microfibrils, thereby producing acylated cellulose fine fibers.

[0017] To avoid reducing the permeability of the modification reaction solution containing the acylating agent into the cellulose, it is preferable to add the acylating agent after defibration has progressed to a certain extent. Adding the acylating agent midway allows the solution containing TAAH, water, and DMSO to sufficiently permeate the cellulose prior to the acylation reaction, expanding the spaces between cellulose microfibrils and disrupting the arrangement of microfibrils. This allows the acylating agent added later to easily act on the cellulose fibrils, promoting the efficiency and uniformity of the modification reaction.

[0018] The cellulose used as a raw material may be in the form of cellulose alone, or may be in a mixed form containing non-cellulose components such as lignin and hemicellulose. Preferred cellulose materials are those containing crystalline cellulose structure type I, such as wood-derived pulp, wood, bamboo, linder pulp, cotton, and materials containing cellulose powder.

[0019] TAAH has the effect of breaking the hydrogen bonds of cellulose and the hydrogen bonds between fibrils. In addition, its basicity promotes the acylation modification reaction of cellulose hydroxyl groups. On the other hand, water is thought to play a role in stabilizing TAAH in DMSO and providing solvation between DMSO and TAAH.

[0020] The tetraalkylammonium hydroxide (TAAH) used in the present invention is not limited as long as the alkyl group has 2 to 4 carbon atoms, but preferred TAAHs are tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH). TAAH is more stable when it contains water, and since water is a component of the modification reaction solution, TAAH can be used in the form of an aqueous solution. Among these, TEAH, TPAH, and TBAH are commercially available as aqueous solutions and are easily available. The tetraalkylammonium hydroxides may be used alone or in combination of two or more.

[0021] On the other hand, tetramethylammonium hydroxide, although basic, was ineffective in promoting the swelling or defibration of cellulose. Furthermore, tetraalkylammoniums with side chains longer than butyl groups are less basic and less soluble in DMSO, making them less effective at promoting the defibration and modification of cellulose, making them undesirable.

[0022] The acylating agent used in the present invention includes vinyl carboxylate, carboxylic acid anhydride, and carboxylic acid, among which vinyl carboxylate is most preferred in order to maintain the reaction efficiency and suppress side reactions. These acylating agents can be used alone or in combination of two or more.

[0023] As the vinyl carboxylate, a vinyl carboxylate represented by the following formula (2) can be used. R1-COO-C(R2)=C(R3)(R4) (2) (In the formula, R1 represents any one of an alkyl group, an alkylene group, a cycloalkyl group, and an aryl group having 1 to 16 carbon atoms, and R2, R3, and R4 represent hydrogen or any one of an alkyl group, an alkylene group, a cycloalkyl group, and an aryl group having 1 to 16 carbon atoms.)

[0024] Furthermore, the vinyl carboxylate is preferably at least one selected from the group consisting of vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl cyclohexanecarboxylate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl pivalate, vinyl octylate, divinyl adipate, vinyl methacrylate, vinyl crotonate, vinyl pivalate, vinyl octylate, vinyl benzoate, vinyl cinnamate, and isopropenyl acetate.

[0025] These vinyl carboxylates can be used alone or in combination of two or more. Among these vinyl carboxylates, lower aliphatic vinyl carboxylates having 2 to 7 carbon atoms (especially 2 to 5), such as vinyl acetate, vinyl propionate, and vinyl butyrate, are preferred from the viewpoint of defibration and reactivity, with C1-4 alkyl vinyl carboxylates being particularly preferred. If the number of carbon atoms is too large, there is a risk of reduced permeability between microfibrils and reduced reactivity with cellulose hydroxyl groups, and therefore it is preferred to use them in combination with lower aliphatic vinyl carboxylates.

[0026] The modification reaction solution of the present invention is composed of TAAH, water, DMSO, and an acylating agent, and is adjusted to a concentration range of 0.1-1.2 wt% TAAH, 0.1-1.8 wt% water, 82-98.8 wt% DMSO, and 1-15 wt% acylating agent. More preferably, the solution is adjusted to a concentration range of 0.15-1.0 wt% TAAH, 0.15-1.6 wt% water, 85.4-97.7 wt% DMSO, and 2-12 wt% acylating agent. Even more preferably, the solution is adjusted to a concentration range of 0.2-0.9 wt% TAAH, 0.2-1.5 wt% water, 85.4-97.7 wt% DMSO, and 3-10 wt% acylating agent.

[0027] A TAAH concentration lower than 0.1 wt% is not preferable because it has little effect on defibration and modification, while a concentration higher than 1.2 wt% is not preferable because it may dissolve cellulose and cause the loss of type I crystal structure.

[0028] A water concentration lower than 0.1 wt% is not preferable because it reduces the degree of cellulose defibration and may cause TAAH to become unstable and decompose, while a water concentration higher than 1.8 wt% is not preferable because it reduces not only the degree of cellulose defibration but also the degree of modification.

[0029] If the acylating agent concentration is less than 1 wt%, it is undesirable because it may reduce the degree of cellulose defibration and the modification rate (hydrophobic effect), while if it exceeds 15 wt%, it is undesirable because it may reduce the degree of defibration due to poor permeability of the modification reaction solution into the cellulose.

[0030] The modification reaction solution of the present invention may contain, in addition to TAAH, water, an acylating agent, and DMSO, other organic solvents, as long as they do not affect the defibrillation and modification reactivity. Examples of other organic solvents include N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and pyridine.

[0031] The amount of cellulose to be added to the modification reaction solution is not a problem even if the acylating agent is in excess relative to the cellulose, as long as the concentration of the acylating agent in the modification reaction solution is within the above-mentioned concentration range. However, since the efficiency of use of the acylating agent is low, the ratio of cellulose to 1 part of acylating agent in the modification reaction solution is preferably 1 / 5 to 3 parts, more preferably 1 / 3 to 1 part, and most preferably 1 / 2 to 1 part.

[0032] The weight ratio of cellulose to the modification reaction solution, taking into account the concentration of the acylating agent in the modification reaction solution and the ratio of the acylating agent to the cellulose, can usually be selected from a range of approximately 0.5 / 99.5 to 25 / 75 (former / latter), for example, 1 / 99 to 20 / 80, preferably 1.5 / 98.5 to 15 / 85, and more preferably 2 / 98 to 12 / 88. If the cellulose content is too low, the production efficiency of cellulose fine fibers will decrease. If the cellulose content is too high, the degree of defibration may decrease due to insufficient penetration of the modification reaction solution between cellulose fibers, lamellae, and microfibrils. Furthermore, if the cellulose content is high, the viscosity of the dispersion increases, reducing the uniformity of the reaction. In either case, productivity and quality may decrease. Furthermore, if the cellulose content is too high, the uniformity of the size and modification rate of the obtained fine fibers may decrease.

[0033] There are no particular limitations on the method for preparing the defibration solution or modification reaction solution of the present invention. For example, a commercially available TAAH aqueous solution is typically prepared to the desired TAAH / water weight ratio, and then DMSO is added to the defibration solution, or DMSO and an acylating agent are added to the modification reaction solution, followed by stirring to obtain the defibration solution or modification reaction solution. If the TAAH concentration of the commercially available TAAH aqueous solution is lower than the desired concentration when the water concentration is adjusted to the optimal range, it is preferable to distill it before use and concentrate it to the desired moisture content before use. If the concentration is higher than the desired concentration, water is added to dilute it before use. There are no particular limitations on the temperature during mixing, but a temperature of 10 to 70°C is preferred.

[0034] The method for modifying cellulose with the modification reaction solution of the present invention is not particularly limited. For example, a dispersion of acylated cellulose microfibers can be obtained by adding cellulose to a predetermined amount of the modification reaction solution of the present invention and stirring at a constant temperature for a constant time. Stirring can be performed using a commonly used mechanical stirrer, but a homogenizer or the like can also be used. For a beaker scale, stirring with a magnetic stirrer is sufficient. The reaction temperature may be 20 to 80°C, and stirring can be performed at room temperature without temperature adjustment. Temperatures below 20°C are not preferred because the modification reaction rate is low. Temperatures above 80°C are also not preferred because cellulose and TAAH may decompose. The most preferred temperature is 20 to 70°C.

[0035] The modification reaction time in the present invention may be adjusted appropriately depending on the type and concentration of TAAH and acylating agent contained in the modification reaction solution and the reaction temperature. For example, it may be about 0.2 to 24 hours, preferably about 0.5 to 12 hours, and more preferably about 1 to 8 hours. When a lower vinyl carboxylate such as vinyl acetate is used, the reaction time may be several hours (e.g., 0.5 to 5 hours), preferably about 1 to 4 hours. Furthermore, as mentioned above, the reaction time may be shortened by increasing the treatment temperature (reaction temperature) or the stirring speed. When a low-boiling acylating agent such as vinyl carboxylate is used, it is preferable to carry out the reaction in a sealed system, a pressurized system, or a reflux system to avoid evaporation. If the reaction time is too short, the modification reaction solution may not penetrate sufficiently between the microfibrils, resulting in insufficient reaction and a reduced degree of defibration. On the other hand, if the reaction time is too long or the temperature is too high, over-modification may occur, resulting in a reduced crystallinity and yield of cellulose fine fibers.

[0036] When the acylating agent is added midway, the device used to swell and / or partially decompose the cellulose with the defibration solution in the first stage is not particularly limited, but an apparatus equipped with the same agitator as that used in the subsequent acylation modification reaction / defibration may be used. The time for the swelling and / or partial decomposition in the first stage may be adjusted appropriately depending on the blending ratio of TAAH, water, and DMSO and the shear force of the agitator. For example, from the viewpoint of efficiency, the time is preferably 5 hours or less, more preferably 4 hours or less, and most preferably 3 hours or less. After adding the acylating agent, it is preferable to carry out the reaction for an additional 0.5 to 5 hours or more to acylate and defibrate the swollen and / or partially decomposed cellulose.

[0037] There are two methods for recovering the acylated modified cellulose fine fibers from the modification reaction / defibration solution, depending on whether or not the modification reaction / defibration solution is recovered and reused as is, but there is no particular limitation.

[0038] For example, if the modification reaction / defibration solution is recovered and reused as is, after the reaction is completed, the solid acylated modified fine fibers and the modification reaction / defibration solution are recovered separately using solid-liquid separation methods such as centrifugation, squeezing, filtration, precipitation, etc. The recovered modification reaction / defibration solution can be used to synthesize the next acylated modified fine fibers after adjusting its composition (e.g., by adding the consumed acylating agent). The acylated modified fine fibers in the solid content are washed to remove the residual modification / defibration solvent. Acylated modified cellulose fine fibers can be obtained by repeating the washing procedure multiple times (for example, about 2 to 5 times). The washing solvent is not particularly limited, and any organic solvent capable of dissolving components other than the modified fine fibers can be used. Examples include water, alcohols, ketones, esters, and toluenes. When modifying with a highly hydrophilic acyl group such as an acetyl group, water or alcohol is particularly preferred. On the other hand, when modifying with a highly hydrophobic acyl group such as a lauryl group, it is preferable to wash with water or alcohol, followed by washing with a low-polarity solvent such as acetone, ester, or toluene, in order to efficiently remove the acylating agent.

[0039] On the other hand, if the modification reaction / defibration solution is not reused, after the reaction is completed, the acylating agent is inactivated with water or methanol, etc., and the modified cellulose fine fibers are recovered by the solid-liquid separation described above, and washed using the same washing method and washing solvent as above.

[0040] The shape of the obtained cellulose fine fibers can be observed using FE-SEM. The acylated modified cellulose fine fibers of the present invention typically have a fiber diameter of several tens to several hundreds of nanometers and a length of several micrometers to several tens of micrometers, but in some cases, they may contain micron-order fine fibers. The microfibrils contained in submicron-order or micron-order fine fibers are loosely disordered, and can be nanosized to several tens of nanometers or less by applying shear force. There are no particular restrictions on the device that applies the shear force, but examples include a twin-screw kneader, a homogenizer, a mass colloider, and a paint shaker.

[0041] The average degree of substitution of the acylated modified cellulose fine fibers of the present invention (the average number of substituted hydroxyl groups per glucose, the basic structural unit of cellulose) can be controlled by adjusting the reaction conditions depending on the application. An average degree of substitution of 0.1 or less is undesirable because the degree of defibration and the hydrophobicity of the resulting fine fibers are low. An average degree of substitution exceeding 1.5 is undesirable because there is a risk of losing the I-type crystalline structure of cellulose. A more preferred range is 0.2 to 1.4, and a most preferred range is 0.4 to 1.3. The average degree of substitution (DS) is the average number of substituted hydroxyl groups per glucose, the basic structural unit of cellulose, and reference can be made to Biomacromolecules 2007, 8, 1973-1978, WO2012 / 124652A1, WO2014 / 142166A1, etc.

[0042] The cellulose fine fibers produced by the present invention can be easily dispersed in organic solvents. The organic solvents in which the cellulose fine fibers can be dispersed depend on the type of acyl group. For example, cellulose fine fibers modified with aliphatic acyl groups having 2 to 3 carbon atoms can be dispersed in polar organic solvents such as alcohols, amides, and tetrahydrofuran. On the other hand, cellulose fine fibers modified with aliphatic acyl groups or aromatic acyl groups having 4 or more carbon atoms can be dispersed in a range of solvents from polar to hydrophobic. For example, cellulose fine fibers modified with butyryl groups, lauryl groups, or benzoyl groups can be dispersed in toluene and dichloromethane. [Example]

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Details of the raw materials used are as follows, and the properties of the obtained modified cellulose fine fibers were measured as follows.

[0044] (Materials and reagents used) Cellulose pulp: NBKP pulp (Canfor) and cotton linter pulp were used. Both were obtained from Marubeni Corporation. The cellulose pulp was shredded to a size suitable for placing in a sample bottle. 40% tetrapropylammonium hydroxide aqueous solution: manufactured by Tokyo Chemical Industry Co., Ltd. 35% tetraethylammonium hydroxide aqueous solution: manufactured by Tokyo Chemical Industry Co., Ltd. 40% tetrabutylammonium hydroxide aqueous solution: manufactured by Tokyo Chemical Industry Co., Ltd. Vinyl carboxylate, DMSO, and other raw materials: reagents manufactured by Nacalai Tesque, Inc.

[0045] (IR spectrum of acylated modified cellulose microfibers) The IR spectrum of the cellulose microfibers was measured using a Fourier transform infrared spectrophotometer (FT-IR). The measurement was performed using a NICOLET MAGNA-IR760 Spectrometer manufactured by NICOLET, in the reflection mode. Acylation modification was observed at a frequency of 1730 cm -1This was confirmed by the absorption band.

[0046] (Evaluation of the average degree of substitution of acylated modified cellulose microfibers) A specified amount of acylated modified cellulose microfibers is dispersed in a mixture of NaOH / EtOH / HO and stirred at room temperature for 4 hours, whereby the ester bonds are hydrolyzed, the acyl groups are removed from the hydroxyl groups of the CNF, and the acylated CNF is converted into unmodified CNF. Meanwhile, the removed acyl groups combine with sodium hydroxide to convert into sodium carboxylate, the number of moles of which can be quantified using the titration method shown below. After hydrolysis, the reaction solution (solvent, sodium carboxylate, and sodium hydroxide) and the residue (unmodified CNF) were separated by filtration. The residue was dried and weighed. The amount of residual sodium hydroxide was determined by titrating the solution with aqueous hydrochloric acid. The number of moles of acyl groups (C) and the average degree of substitution of acyl groups (DS) were calculated using the following formula: A = the equivalent number of sodium hydroxide added to the hydrolysis solution, W = the weight of the CNF recovered and dried after hydrolysis, and B = the equivalent number of hydrochloric acid consumed in titration. Number of moles of cellulose (anhydroglucan) (M) = W / 162 Number of moles of acyl groups C=AB Average degree of substitution DS=C / M

[0047] (SEM observation) The shape of the cellulose fine fibers was observed using FE-SEM (JEOL Ltd. "JSM-6700F", measurement conditions: 20 mA, 60 seconds).

[0048] (Evaluation of organic solvent dispersibility of acylated modified cellulose microfibers) The dispersibility of acylated cellulose fine fibers in an organic solvent is a parameter that reflects the acylation rate and the degree of defibration. In the present invention, the dispersibility is evaluated by the following method. Washed acylated modified cellulose fine fibers (dry weight 0.05 g) and 10 g of dispersion solvent were placed in a 20 ml sample bottle, stirred thoroughly with a stirrer, and then left to stand at room temperature for 6 hours before observation. If no precipitation occurred, the dispersion was judged to be good. On the other hand, if precipitation occurred, the dispersion was evaluated as undispersible.

[0049] (Evaluation of crystallinity of acylated modified cellulose microfibers) The dispersion of acylated modified cellulose microfibers was dried and the crystallinity was measured using powder X-ray crystal diffraction (XRD). The analysis was performed using an X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation). The measurement conditions are as follows: ·X-ray:Cu / 40kV / 40mA Scan speed: 10° / min Scanning range: 2θ=5~70° The crystallinity was calculated using the following formula (see Textile Res. J. 29:786-794, 1959). Crystallinity (%)=[(I200-IAM) / I200]×100 I200: Diffraction intensity at 2θ=22.6° IAM: Diffraction intensity of amorphous part at 2θ=18.5°

[0050] Example 1 0.1 g of 40% aqueous tetrapropylammonium hydroxide (TPAH) solution and 5 g of dimethyl sulfoxide were placed in a 10 ml sample bottle and stirred at 23 °C with a magnetic stirrer until the mixture was uniform. Next, 0.23 g of cotton linter pulp was added and stirred for 1 hour, after which 0.25 g of vinyl acetate was added and stirred for 1 hour for acetylation modification. Next, the modified reaction solution (TPAH, vinyl acetate, and DMSO) and by-product (acetaldehyde) were removed by washing with distilled water. The modification of the obtained cellulose microfibers was confirmed by FT-IR analysis, and the IR spectrum (Figure 1) showed a frequency of 1730 cm -1 A strong absorption band was detected near the center. Furthermore, the average degree of substitution and crystallinity were evaluated, and found to be 1.3 and 68%, respectively (Table 1). Figure 2 shows the results of SEM observation of the morphology. Most cellulose fine fibers have a fiber diameter ranging from several tens to several hundreds of nanometers, and lengths ranging from several micrometers to several tens of micrometers. When acetylated fine fibers were dispersed in solvents such as ethanol, isopropanol, tetrahydrofuran, and dichloromethane, the resulting dispersion did not exhibit layer separation due to sedimentation even when left to stand at room temperature.

[0051] Example 2 The same experiment and evaluation were carried out as in Example 1, except that the amounts of 40% TPAH aqueous solution and vinyl acetate added were changed to 0.06 g and 0.15 g, respectively. The results are shown in Figure 1 (IR spectrum), Figure 3 (SEM photograph), and Table 1 (average degree of substitution and crystallinity), respectively. By reducing the amounts of TPAH aqueous solution and vinyl acetate added, the modification rate decreased, but the degree of defibration remained almost unchanged. Observation of the shape with SEM revealed that the fiber diameter of most cellulose fine fibers ranged from several tens to several hundreds of nanometers, and the length ranged from several micrometers to several tens of micrometers. Acetylated fine fibers were dispersed in solvents such as ethanol, isopropanol, tetrahydrofuran, and dichloromethane, and the resulting dispersion did not exhibit layer separation due to sedimentation even when left to stand at room temperature.

[0052] Example 3 The same procedure as in Example 2 was carried out and evaluated, except that the reaction temperature was changed to 55°C. The results are shown in Figure 4 and Table 1. The crystallinity was almost the same as in Example 2, but the average degree of substitution was higher than in Example 2. When the shape was observed with an SEM, some coarse fibers were observed, but most of the cellulose fine fibers had fiber diameters ranging from several tens to several hundreds of nm and lengths ranging from several μm to several tens of μm. The acetylated fine fibers were dispersed in solvents such as ethanol, isopropanol, tetrahydrofuran, and dichloromethane, and the resulting dispersion did not show layer separation due to sedimentation even when left to stand at room temperature.

[0053] Example 4 The same experiment and evaluation were carried out as in Example 2, except that a 40% TBAH aqueous solution was used instead of the 40% TPAH aqueous solution. The results are shown in Figure 1 (IR spectrum), Figure 4 (SEM photograph), and Table 1 (average degree of substitution and crystallinity). Observation of the morphology using an SEM revealed that some coarse fibers were observed, but most of the cellulose fine fibers had fiber diameters ranging from several tens to several hundreds of nanometers and lengths ranging from several micrometers to several tens of micrometers. Acetylated fine fibers were dispersed in solvents such as ethanol, isopropanol, tetrahydrofuran, and dichloromethane, and the resulting dispersion did not exhibit layer separation due to sedimentation even when left to stand at room temperature. It was found that TBAH has a defibration-promoting effect almost equivalent to that of TPAH.

[0054] Example 5 The same experiment and evaluation were carried out as in Example 2, except that a 40% TEAH aqueous solution was used instead of the 40% TPAH aqueous solution. The results are shown in Figure 5 (SEM photograph) and Table 1 (average degree of substitution and crystallinity), respectively. The crystallinity was almost the same as in Example 2. The average degree of substitution was higher than in Example 2, but the content of coarse fibers increased. The defibration-promoting effect was slightly lower than in TPAH, but dispersibility in organic solvents was almost unchanged.

[0055] Example 6 The same procedure as in Example 2 was repeated, except that Canfor pulp was used instead of Cotton linter pulp. The results are shown in Figure 1 (IR spectrum), Figure 6 (SEM photograph), and Table 1 (average degree of substitution and crystallinity). The evaluation results revealed that equivalent modification and defibration degrees could be obtained even when the cellulose raw material was changed.

[0056] Example 7 Acetylated modified cellulose fine fibers were prepared and evaluated in the same manner as in Example 1, except that pre-swelling / defibration was not performed and vinyl acetate was added from the beginning and stirred for 2 hours. The average degree of substitution of the obtained cellulose fine fibers was 1.31 and the crystallinity was 65% (Table 1). The IR spectrum is shown in Figure 1 and the SEM photograph in Figure 7. The SEM observation revealed that there were more coarse fibers than in Example 1, but the fine fibers had almost the same shape and size as those in the examples.

[0057] Comparative Example 1 The acylation modification reaction of cellulose was carried out in the same manner as in Example 6, except that the aqueous tetrapropylammonium hydroxide solution was not added. The solid matter was washed and recovered in the same manner as in Example 1. An SEM photograph of the recovered solid matter is shown in Figure 8. Coarse fibers similar to the raw pulp fibers were observed. FT-IR analysis (Figure 1) showed that almost no modification had occurred.

[0058] Comparative Example 2 A cellulose acylation modification reaction was carried out in the same manner as in Example 1, except that the amount of 40% tetrapropylammonium hydroxide (TPAH) aqueous solution added was changed to 0.18 g. The solid matter was recovered by washing in the same manner as in Example 1. The average degree of substitution of the recovered acetylated cellulose fine fibers was 1.13, and the crystallinity had decreased to 45%. From these results, it is believed that a portion of the cellulose was completely dissolved and converted to cellulose acetate.

[0059] Table 1 shows the compositions of the modification reaction solutions and reaction conditions of Examples 1 to 7 and Comparative Examples 1 and 2, as well as the average degrees of substitution and crystallinity of the resulting cellulose fine fibers. [Table 1] [Industrial Applicability]

[0060] The modified cellulose fine fibers of the present invention can be used in various composite materials and coating agents, and can also be formed into sheets or films for use.

Claims

1. The method includes impregnating cellulose with a modification reaction solution containing tetraalkylammonium hydroxide represented by the following formula (1), water, dimethyl sulfoxide, and an acylating agent, to acylate-modify the cellulose and defibrate it, the component ratios of the tetraalkylammonium hydroxide, water, methyl sulfoxide, and acylating agent in the modification reaction solution are 0.1 to 1.2 wt % of tetraalkylammonium hydroxide, 0.1 to 1.8 wt % of water, 82.0 to 98.8 wt % of dimethyl sulfoxide, and 1.0 to 15.0 wt % of the acylating agent relative to the total amount of the tetraalkylammonium hydroxide, water, methyl sulfoxide, and acylating agent; A method for producing acylated modified cellulose fine fibers. R ４ N ＋ OH － (1) (wherein each R independently represents an alkyl group having 2 to 4 carbon atoms).

2. The method comprises: impregnating cellulose with a solution containing a tetraalkylammonium hydroxide represented by the following formula (1), water, and dimethyl sulfoxide to swell and / or partially decompose the cellulose; then adding an acylating agent to the solution to form a modification reaction solution; and acylating and defibrating the swollen and / or partially decomposed cellulose, the component ratios of the tetraalkylammonium hydroxide, water, methyl sulfoxide, and acylating agent in the modification reaction solution are 0.1 to 1.2 wt % of tetraalkylammonium hydroxide, 0.1 to 1.8 wt % of water, 82.0 to 98.8 wt % of dimethyl sulfoxide, and 1.0 to 15.0 wt % of the acylating agent relative to the total amount of the tetraalkylammonium hydroxide, water, methyl sulfoxide, and acylating agent; A method for producing acylated modified cellulose fine fibers. R ４ N ＋ OH － (1) (wherein each R independently represents an alkyl group having 2 to 4 carbon atoms).

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