Hydrophobically modified cellulose fiber and method for producing same

Abstract

Provided is a method for efficiently producing a hydrophobically modified cellulose fiber using a small amount of a hydrophobic modifier. A method for producing cellulose fibers, which solves the technical problem, comprises: a step for mixing cellulose fibers, an alkali, and water to prepare an aqueous solution in which the concentration of cellulose fibers is 0.5-50 mass% and the concentration of the alkali is 1-10 mass%; a step in which a cyclic amide compound is added to the aqueous solution in an amount of 0.2-10 equivalents (inclusive) relative to the amount of anhydrous glucose units contained in the cellulose fibers, and the cellulose fibers and the cyclic amide compound are reacted; and a step for further adding an acid to the aqueous solution to neutralize the base.

Description

Technical Field

[0001] The invention relates to hydrophobically modified cellulose fibers and a method for preparing the same. Background Art

[0002] In recent years, research is being conducted to reduce the emission of greenhouse gases by replacing existing various composite materials by making the materials derived from biomass composite. As one of the materials derived from biomass, known cellulose fiber. Cellulose fiber has high hydrophilicity due to the OH group of glucose unit contained in the molecular structure of cellulose. However, the high hydrophilic cellulose has low compatibility with organic solvents and resins, and there is a technical problem that is difficult to be used in composite materials as is.

[0003] Therefore, various methods have been tried to hydrophobically modify cellulose fibers. Among them, a method of hydrophobically modifying cellulose fibers by reacting acetic anhydride with cellulose fibers is widely known (for example, Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-75950 Summary of the invention

[0007] Problems to be solved by the invention

[0008] However, in the method described in Patent Document 1, a large amount of acetic anhydride is required when performing the hydrophobic modification treatment. The reason is as follows. Cellulose fibers have the property of agglomerating if dehydrated. Therefore, the hydrophobic modification treatment is performed by dispersing the cellulose fibers in water. However, if acetic anhydride is added to the cellulose fiber aqueous solution, the acetic anhydride and water react irreversibly to generate acetic acid. That is, the acetic anhydride is consumed by water before reacting with the cellulose fibers, and the hydrophobic modification treatment of the cellulose fibers will not be fully performed. Therefore, when performing the hydrophobic modification treatment, it is necessary to add acetic anhydride for reacting with all the water present in the system and acetic anhydride for hydrophobic modification treatment of the cellulose fibers, and a large amount of acetic anhydride is required.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for efficiently producing hydrophobically modified cellulose fibers using a small amount of a hydrophobic modifying agent, and hydrophobically modified cellulose fibers obtained by the method.

[0010] Solutions for solving problems

[0011] The present invention provides a method for producing hydrophobically modified cellulose fibers, which comprises the following steps: a step of mixing cellulose fibers, an alkali and water to prepare an aqueous solution having a cellulose fiber concentration of 0.5 mass % or more and 50 mass % or less; a step of adding a cyclic amide compound in an amount of 0.2 equivalents or more and 10 equivalents or less relative to the amount of anhydrous glucose units contained in the cellulose fibers to the aqueous solution to react the cellulose fibers with the cyclic amide compound; and a step of further adding an acid to the aqueous solution to neutralize the alkali.

[0012] The present invention also provides a hydrophobically modified cellulose fiber, which is a hydrophobically modified cellulose fiber, wherein the OH group of cellulose constituting the cellulose fiber has a structure formed by ring-opening polymerization of a cyclic amide compound.

[0013] Effects of the Invention

[0014] According to the method for producing hydrophobically modified cellulose fibers of the present invention, hydrophobically modified cellulose fibers can be efficiently produced with a small amount of hydrophobic modifier. In addition, the hydrophobically modified cellulose fibers obtained by the production method have high affinity with resins and organic solvents and can be applied to various composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 These are photographs showing the state of a composition in which the hydrophobically modified cellulose fibers obtained in Examples 1, 3, 4, and 8 were dispersed in an epoxy resin.

[0016] Figure 2 These are photographs showing the state of a composition in which the (hydrophobic) modified cellulose fibers obtained in Example 11, Comparative Example 1, Comparative Example 3, and Comparative Example 7 were dispersed in an epoxy resin.

[0017] Figure 3 This is a photograph showing the state of a composition in which the hydrophobically modified cellulose fibers obtained in Examples 12 and 13 were dispersed in an epoxy resin. DETAILED DESCRIPTION

[0018] 1. Method for producing hydrophobically modified cellulose fibers

[0019] The invention relates to a method for preparing hydrophobically modified cellulose fibers, which performs hydrophobic modification on the cellulose fibers to improve the affinity of the cellulose fibers with various resins and organic solvents.

[0020] As mentioned above, when acetic anhydride is used as a hydrophobic modifier, a large amount of acetic anhydride is needed, and from the viewpoints of cost, manufacturing efficiency, etc., there are technical problems. In contrast, in the manufacture method of the present invention, a cyclic amide compound is used as a hydrophobic modifier. Although the cyclic amide compound reacts with the water in the system, its reaction is reversible. Therefore, when cellulose fiber is hydrophobically modified, the hydrophobic modifier (cyclic amide compound) will not be consumed by the reaction with water, and can be efficiently processed with a small amount of hydrophobic modifier.

[0021] The method for producing hydrophobically modified cellulose fibers of the present invention specifically includes the following steps: a step of mixing cellulose fibers, an alkali and water to prepare an aqueous solution having a cellulose fiber concentration of 0.5% by mass or more and 50% by mass or less (hereinafter also referred to as the "aqueous solution preparation step"); a step of adding a cyclic amide compound in an amount of 0.2 equivalents or more and 10 equivalents or less relative to the amount of anhydrous glucose units contained in the cellulose fibers to the aqueous solution to react the cellulose fibers with the cyclic amide compound (hereinafter also referred to as the "cyclic amide compound reaction step"); and a step of further adding an acid to the aqueous solution to neutralize the alkali (hereinafter also referred to as the "neutralization step").

[0022] In the method for producing hydrophobically modified cellulose fibers of the present invention, the reaction is carried out as shown in the chemical reaction formula below. It should be noted that Cell in the following formula represents a residue from which an OH group is removed from the cellulose fibers. In addition, the following chemical reaction formula only shows one OH group of the cellulose fibers, but the cellulose fibers have multiple OH groups on the surface, and the same reaction actually occurs on multiple OH groups of the cellulose fibers.

[0023] In addition, the OH group represented in the following chemical reaction formula can be any OH group in the glucose unit in the molecular structure of cellulose (fiber). That is, the glucose unit has three OH groups, and the OH groups at any position can react with the cyclic amide compound as described below. In the reaction, only one OH group in the glucose unit can react with the cyclic amide compound, two OH groups can react with the cyclic amide compound separately, or all three OH groups can react with the cyclic amide compound. In the present application, it is believed that the OH group at the 6th position of the glucose unit is particularly susceptible to reaction with the cyclic amide compound.

[0024] In the manufacturing method of the present invention, first, in the aqueous solution preparation step, cellulose fibers, alkali (NaOH in the following chemical reaction formula) and water are mixed to prepare an aqueous solution containing cellulose fibers and alkali. Then, in the cyclic amide compound reaction step, when a cyclic amide compound (N-methylpyrrolidone (also referred to as "NMP") in the following formula) is added to the aqueous solution, the alkali in the system is used to reversibly open the cyclic amide compound. In addition, the cyclic amide compound reacts with the OH groups (OH groups) on the surface of the cellulose fibers treated with alkali. - Na + Next, in the neutralization step, when an acid (an organic acid (R-COOH, R- is an arbitrary organic group) in the following chemical reaction formula) is added to the aqueous solution, the base in the system is neutralized, and the amine derived from the cyclic amide compound reacts with the organic acid to generate an amide bond.

[0025] [Chemical formula 1]

[0026]

[0027] Through the above series of steps, hydrophobic groups are introduced on the surface of the cellulose fiber, and the cellulose fiber is subjected to hydrophobic modification. It should be noted that in the neutralization step, it is not necessary to react the acid with the amine derived from the cyclic amide compound, for example, the base in the system can also be neutralized by only the acid. Below, each step of the production method is described in detail.

[0028] (1) Aqueous solution preparation process

[0029] In the aqueous solution preparation step, cellulose fibers, an alkali, and water are mixed to prepare an aqueous solution having a cellulose fiber concentration of 0.5 mass % to 50 mass %.

[0030] In order to suppress side reactions, the water used in this step is preferably ion-exchanged water.

[0031] In addition, the cellulose fiber used in this process can be a fibrous fiber containing cellulose, and a part of it can also contain components other than cellulose, such as hemicellulose, lignin, etc. In the case where the components other than cellulose contain hydroxyl groups, such as hemicellulose, the hydroxyl groups may react with cyclic amide compounds. Therefore, in the case where the cellulose fiber contains hemicellulose, etc., it is preferred to consider the amount of hydroxyl groups contained in the components other than cellulose and adjust (increase) the amount of cyclic amide compounds. It should be noted that, from the viewpoint of effectively carrying out the above-mentioned hydrophobic modification treatment, the ratio of cellulose in the cellulose fiber is preferably 30% by mass or more, more preferably 60% by mass or more. The concentration of cellulose in the cellulose fiber can be determined by comprehensively evaluating multiple analysis results. Specifically, hemicellulose, lignin, etc. are non-crystalline, so by performing sugar analysis using X-ray diffraction, ion chromatography, etc., the cellulose amount in the cellulose fiber can be determined.

[0032] In addition, the crystallinity of the cellulose fiber is preferably 50% or more, more preferably 60% or more. If the crystallinity of the cellulose fiber is 50% or more, when the obtained hydrophobically modified cellulose fiber is used in various composite materials, the mechanical strength of the composite material is easily improved. It should be noted that the crystallinity is expressed by (crystalline region of cellulose) / {(crystalline region of cellulose)+(non-crystalline region of cellulose)+(region derived from non-cellulose (non-crystalline region)}×100, which can be determined by X-ray diffraction as described above. As a more specific calculation method, the segal method is known.

[0033] The raw materials of cellulose fibers are not particularly limited, and examples of raw materials include pulp obtained from wood, bamboo, hemp, jute, kenaf, cotton, sugar beet, agricultural product waste, cloth, etc.; recycled materials such as rayon and cellophane. In addition, the above-mentioned pulp can also be chemical pulp obtained by chemically or mechanically treating plant raw materials. Specifically, it can be any pulp selected from sulfite pulp, semi-chemical pulp, chemical groundwood pulp, chemical mechanical pulp, groundwood pulp, disc mechanical pulp, thermomechanical pulp, chemical thermomechanical pulp, deinked waste paper pulp, corrugated waste paper pulp, magazine waste paper pulp, etc. It should be noted that the cellulose fibers in this specification include not only completely fibrous fibers, but also include, for example, cellulose fibers that are agglomerated into particles, or processed or formed into any shape.

[0034] The average fiber diameter of the cellulose fiber that can be used in this process is 0.02 μm or more, preferably 1 μm or more and 100 μm or less, and more preferably 5 μm or more and 60 μm or less. If the average fiber diameter of the cellulose fiber is 1 μm or more and 100 μm or less, it can be obtained cheaply and has good operability. In addition, the average fiber length is preferably 100 μm or more and 10000 μm or less, and more preferably 200 μm or more and 5000 μm or less. If the average fiber length of the cellulose fiber is within the above range, it is easy to use the obtained hydrophobic modified cellulose fiber for various purposes.

[0035] The average fiber diameter and fiber length described above vary depending on the diameters measured, and are average values ​​obtained by measuring the fiber diameters and fiber lengths of 100 or more cellulose fibers by morphological observation using an optical microscope, electron microscope, AFM or the like.

[0036] In addition, the base can be any compound that can open the ring of the cyclic amide compound in the cyclic amide compound reaction step described later, and promote the reaction between the OH group of the cellulose fiber and the ring-opened body of the cyclic amide compound. The base is preferably a compound that can make the pH of the aqueous solution be 11 or more. If the pH of the aqueous solution is 11 or more, it is easy to promote the above reaction. Examples of bases used in this process include inorganic bases such as alkali metal hydroxides and alkaline earth metal hydroxides; organic bases such as amine compounds. Specific examples of alkali metal hydroxides and alkaline earth metal hydroxides as inorganic bases include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, and barium hydroxide. In addition, examples of amine compounds as organic bases include tertiary amine compounds such as triethylamine, diazabicycloundecene, and diazabicyclononene. In this process, only one of them can be used, or two or more can be used in combination. Among them, from the perspective of low cost and rapid processing of cellulose fibers, sodium hydroxide and trimethylamine are preferred, and from the perspective of enabling the reaction to proceed stably, diazabicycloundecene and diazabicyclononene are more preferred.

[0037] Here, the method for mixing the cellulose fibers, alkali, and water in the aqueous solution preparation step is not particularly limited, and a mixing method that does not change the crystal structure of cellulose is preferred. When the cellulose fibers come into contact with an aqueous solution with a high alkali concentration, the crystal structure of cellulose may change. Therefore, in this step, it is preferred to prepare a solution obtained by dispersing cellulose fibers in water and a solution obtained by dispersing alkali in water separately and mix them.

[0038] In addition, the concentration of the cellulose fiber in the aqueous solution prepared in this step can be 0.5% by mass or more and 50% by mass or less, preferably 1% by mass or more and 30% by mass or less. If the concentration of the cellulose fiber in the aqueous solution is 0.5% by mass or more, the cellulose fiber can be efficiently subjected to hydrophobic modification. On the other hand, if the concentration of the cellulose fiber is too high, the viscosity of the aqueous solution becomes high and is difficult to handle, but if it is 50% by mass or less, the viscosity of the aqueous solution can be controlled within a desired range.

[0039] In addition, when using an inorganic base such as an alkali metal hydroxide or an alkaline earth metal hydroxide as a base, the concentration of the inorganic base of the aqueous solution prepared in this step is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 8% by mass or less. If the concentration of the inorganic base is 1% by mass or more, then in the cyclic amide compound reaction step described later, the cyclic amide compound and the cellulose fiber react easily. On the other hand, if the concentration of the inorganic base is 10% by mass or less, it is not easy to affect the crystal structure of cellulose. On the other hand, when using the above-mentioned amine compound as a base, the addition amount of the alkali (amine compound) is appropriately selected according to its type, etc., as long as it is an amount that can make the pH of the aqueous solution be more than 11 as described above.

[0040] It should be noted that in this process, it is preferred that after the cellulose fibers, alkali and water are mixed, they are fully stirred. The stirring time and stirring method are appropriately selected according to the amount of the aqueous solution, the viscosity (the concentration of the cellulose fibers), etc. When heat is generated by mixing, the crystal structure of cellulose is likely to change, or the cellulose is likely to decompose. Therefore, when mixing, it is preferred to stir multiple times while setting a time interval, or stir in small amounts one by one.

[0041] In addition, after the cellulose fibers, alkali and water are mixed, the aqueous solution may be concentrated as needed. The concentration method is not limited, and filtration can be cited as an example. In this case, the concentration amount is preferably adjusted so that the concentration of the cellulose fibers in the concentrated aqueous solution is 0.5 mass % or more and 50 mass % or less, preferably 1 mass % or more and 30 mass % or less.

[0042] (2) Cyclic amide compound reaction step

[0043] The cyclic amide compound reaction step is a step of adding a predetermined amount of a cyclic amide compound to the aqueous solution to react the cellulose fibers with the cyclic amide compound.

[0044] Cyclic amide compounds are compounds having a cyclic structure and having an amide bond, i.e., -NHCO- structure, in the cyclic part, as long as they are compounds that open the ring in the presence of a base and form an ester bond with the OH group on the surface of the cellulose fiber. Examples of cyclic amide compounds include: N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, N-methyl-ε-caprolactam, 2-pyrrolidone, ε-caprolactam, N-dimethylpropylene urea, 1,3-dimethyl-2-imidazolidinone, and various lactams other than them. Only one of them can be used, or two or more can be used in combination. Among them, N-methyl-2-pyrrolidone is preferred from the viewpoints of good reactivity and easy availability. N-methyl-2-pyrrolidone is also suitable in terms of molecular size close to TEMPO (2,2,6,6-tetramethylpiperidinyl oxide), which is known to react with the OH groups inside the crystal structure of cellulose fibers (in order to maintain the crystal structure) and with the OH groups on the surface of cellulose fibers.

[0045] In addition, the amount of the cyclic amide compound added to the aqueous solution in this process is as long as the equivalent of the amount of anhydrous glucose units of the cellulose fibers in the aqueous solution (hereinafter also referred to as "AGU") is 0.2 or more and 10 or less, AGU is preferably 0.7 or more and 10 or less, and AGU is more preferably 0.7 or more and 1.0 or less. If AGU is 0.2 or more, the cellulose fibers can be fully hydrophobically modified. In addition, if AGU is 0.7 or more, a hydrophobically modified cellulose fiber with a higher affinity for resins and organic solvents can be obtained. On the other hand, if AGU is 10 or less, the amount of the remaining cyclic amide compound remaining in the system can be reduced. In addition, if AGU is 1.0 or less, a hydrophobically modified cellulose fiber can be efficiently obtained with less hydrophobic modifier. It should be noted that the amount of anhydrous glucose units contained in the cellulose fibers is calculated according to the mass of the cellulose fibers in the aqueous solution. In addition, the cellulose fibers are wood powder, lignocellulose, etc., and when lignin is included, the amount of lignin is calculated by excluding the mass of the cellulose fibers.

[0046] In this process, it is preferred that after adding the cyclic amide compound, the aqueous solution is stirred to allow the cyclic amide compound to fully react with the cellulose fibers. The temperature of the aqueous solution at this time is preferably above 5°C and below 90°C, more preferably above 10°C and below 60°C. The stirring time and stirring method can be appropriately selected according to the amount and viscosity of the aqueous solution. In the case of the above stirring, in order to suppress the heat caused by stirring, the change in the crystal structure of cellulose or the decomposition of cellulose caused by the alkali in the system, it is preferred to cool the stirring container using a refrigerant, etc., and stir multiple times while setting the time interval.

[0047] (3) Neutralization process

[0048] In the neutralization step, an acid is added to the aqueous solution to neutralize the base. In this step, not only the base can be neutralized, but also the acid can be reacted with the amino group derived from the cyclic amide compound.

[0049] The type of acid used in this step is not particularly limited, and it may be, for example, an inorganic acid such as hydrochloric acid, or an organic acid, more preferably an organic acid. When an organic acid is used as the acid, the organic acid reacts with the amino group derived from the cyclic amide compound to produce an amide bond. As a result, the organic chain present on the surface of the cellulose fiber becomes longer, and the hydrophobicity of the obtained hydrophobically modified cellulose fiber is further improved.

[0050] Examples of organic acids include: acetic acid; fatty acids having 3 to 16 carbon atoms such as propionic acid and butyric acid; dicarboxylic acids having 2 to 15 carbon atoms such as oxalic acid; aromatic carboxylic acids such as benzoic acid, phthalic acid, and salicylic acid; and compounds having an aromatic ring and containing a carboxyalkylamino group represented by the following chemical formula (hereinafter also referred to as "CP-MABA"). Among them, acetic acid and CP-MABA are preferred from the viewpoint of easy availability.

[0051] [Chemical formula 2]

[0052]

[0053] In the above formula, X represents an alkali metal atom or a hydrogen atom.

[0054] The amount of the acid used is appropriately selected depending on the amount of the base, and the acid may be added until the aqueous solution becomes neutral.

[0055] Furthermore, after adding the acid, the hydrophobically modified cellulose fibers may be further subjected to a step of washing or drying, if necessary.

[0056] 2. About hydrophobic modification of cellulose fibers

[0057] The present invention also provides a hydrophobically modified cellulose fiber produced by the above method, that is, a hydrophobically modified cellulose fiber having a structure formed by ring-opening polymerization of the above cyclic amide compound on the OH group of cellulose (fiber). It should be noted that in the hydrophobically modified cellulose fiber, the amine terminal generated by the ring-opening of the above cyclic amide compound may remain as it is, or the above structure derived from an organic acid may be further bonded to the amine.

[0058] The hydrophobically modified cellulose fibers include, for example, the following structure.

[0059] [Chemical formula 3]

[0060]

[0061] In the above general formula, Cell represents a residue formed by removing an OH group from a glucose unit constituting cellulose. In addition, X represents a divalent residue formed by removing a carboxyl group and an amine from the ring-opened form of the above cyclic amide compound, and is preferably an alkylene group having 2 or more and 6 or less carbon atoms. 1 represents hydrogen or an alkyl group having 1 to 6 carbon atoms, and is preferably hydrogen or methyl. 2 represents hydrogen or a monovalent group having 1 to 10 carbon atoms. 2 The structure of the compound may contain a carboxyl group, a carbonyl group, an amino group, a halogen group, an aromatic group, an alkyl group, etc. 2 Specific examples include the groups derived from organic acids described in the above production method, preferably methyl and chlorophenylmethylaminobutyl.

[0062] Here, cellulose (fiber) contains multiple OH groups in its molecular structure, but it is not necessary to ring-open polymerize the above-mentioned cyclic amide compound on all OH groups. It is sufficient to contain a structure formed by ring-opening polymerization of the above-mentioned cyclic amide compound and at least a part of the OH groups. The structure can be determined, for example, by analysis using NMR, etc. In addition, the amount of the structure formed by ring-opening polymerization of the cyclic amide compound contained in the hydrophobically modified cellulose fiber can be an amount that can obtain affinity with the target resin, organic solvent, etc. and does not affect the crystal structure of cellulose, and can be appropriately selected according to the types of these resins and organic solvents.

[0063] The hydrophobic modified cellulose fiber of the present invention has a high affinity with various resins and organic solvents because the hydrophobic groups shown in the above formula are bonded to the cellulose fiber. Therefore, it can be easily made into a composite material by mixing with a thermosetting resin, a thermoplastic resin, and an organic solvent. Such a composite material can be used for various purposes such as electrical products, building materials, vehicles such as automobiles and trams, and aircraft.

[0064] Example

[0065] Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the technical scope of the present invention is not limited thereto.

[0066] A. Evaluation of dispersibility of cellulose fibers

[0067] [Example 1]

[0068] (1) Aqueous solution preparation step (preparation of alkali-containing cellulose fiber aqueous solution)

[0069] 20 g (absolute dry weight) of cellulose fibers (KC Flock W-50GK, manufactured by Nippon Paper Industries) having an absolute dryness of 95.1% was immersed in 86 g of ion exchange water. In addition, 32 g of sodium hydroxide and 262 g of ion exchange water were mixed to prepare an alkaline aqueous solution. Then, these were mixed to obtain an aqueous solution having a cellulose fiber concentration of 5% by mass and an alkali (NaOH) concentration of 8% by mass.

[0070] The obtained aqueous solution was divided into 100 g portions, and each portion was stirred three times for 200 seconds at 2000 rpm and 97.9 kPa (normal pressure) using Awatori Rentaro (vacuum type, ARV-310P, manufactured by THINKY Co., Ltd.) (the interval after each stirring was 600 seconds). The stirred mixed aqueous solution was filtered, and the filtrate residue was used as an alkali-containing cellulose fiber aqueous solution. It should be noted that for the alkali-containing cellulose fiber aqueous solution, the solid content (alkali-containing cellulose fiber) concentration calculated based on the mass of the residue was 18.5% by mass, and a portion was added dropwise to a pH test paper, and the pH was above 11.

[0071] (2) Cyclic amide compound reaction step

[0072] 0.29 g of N-methylpyrrolidone (NMP, cyclic amide compound) was added to 10.8 g of the alkali-containing cellulose fiber aqueous solution prepared by the above process (the amount of alkali-containing cellulose fiber: 2 g). The amount of NMP was equivalent to 0.24 equivalents of anhydrous glucose units (AGU) in the cellulose fiber. Then, the mixture was stirred six times for 60 seconds at 2000 rpm and 97.9 kPa (normal pressure) using Awatori Rentaro (vacuum type, ARV-310P, manufactured by THINKY Co., Ltd.) (the interval after each stirring was 600 seconds).

[0073] (3) Neutralization process

[0074] 20 g of ion exchange water was added to the stirred aqueous solution, and then 10% by mass acetic acid aqueous solution was added until the aqueous solution became neutral. 100 g of ion exchange water was added to the neutralized aqueous solution and suction filtered. Then, suction was stopped, 100 g of ion exchange water was added, and suction filtered again. This operation was repeated 9 times, and the mixture was fully washed and dehydrated. The dehydrated mixture was heated at 105° C. for 3 hours to obtain a hydrophobically modified cellulose fiber in an absolutely dry state.

[0075] [Examples 2 to 5]

[0076] Hydrophobically modified cellulose fibers were obtained in the same manner as in Example 1 except that the amount of NMP added (AGU) in the reaction step of the cyclic amide compound was changed to the value shown in Table 1.

[0077] [Examples 6 to 10]

[0078] Hydrophobically modified cellulose fibers were obtained in the same manner as in Examples 1 to 5 except that the acid in the neutralization step was changed to 10% by mass hydrochloric acid.

[0079] [Example 11]

[0080] Hydrophobically modified cellulose fibers were obtained in the same manner as in Example 4 except that the acid in the neutralization step was changed to the CP-MABA solution (chlorophenylmethylaminobutyric acid (CPMABA) as an organic acid). CP-MABA was prepared as follows.

[0081] Preparation of CP-MABA solution

[0082] The distillation residue of the washing drainage of the polyphenylene sulfide (PPS) polymerization reaction product is treated with hydrochloric acid to a pH of about 1 to acidify the oligomers and perform solid-liquid separation. Then, caustic soda is added to the filtrate to a pH of about 4 to obtain a CP-MABA solution (brown oil) with a CP-MABA content of 80.7%. The obtained CP-MABA solution is used as an organic acid. The purity is analyzed by high performance liquid chromatography (HPLC).

[0083] [Comparative Examples 1 and 4]

[0084] Modified cellulose fibers were obtained in the same manner as in Example 1 or 6 except that the reaction step of the cyclic amide compound was not performed.

[0085] [Comparative Examples 2 and 5]

[0086] Hydrophobically modified cellulose fibers were obtained in the same manner as in Example 1 or 6 except that the amount of NMP added (AGU) in the reaction step of the cyclic amide compound was changed to the value shown in Table 1.

[0087] [Comparative Examples 3 and 6]

[0088] Hydrophobically modified cellulose fibers were obtained in the same manner as in Example 1 or 6 except that methanol (MeOH) was used instead of NMP in the reaction step of the cyclic amide compound.

[0089] [Comparative Example 7]

[0090] For 6g (absolute dry mass) of cellulose fiber (KC Flock W-50GK, made by Nippon Paper Manufacturing Co., Ltd.) and 0.3g of absorbed water, 24g of 1,8-diazabicyclo [5.4.0] -7-undecene (also known as "DBU") was added to make a mixed solution. The concentration of cellulose fiber in the mixed solution was 20% by mass and the alkali concentration was 77% by mass. The mixed solution was stirred 10 times for 60 seconds at 2000rpm and 97.9kpa (normal pressure) (the interval time after the end of one stirring was 600 seconds). The stirred mixed solution was neutralized in the same manner as in Example 4 to obtain hydrophobically modified cellulose fiber.

[0091] [Examples 12 and 13]

[0092] For 6g (absolute dry mass) of cellulose fiber (KC Flock W-50GK, made by Nippon Paper Manufacturing Co., Ltd.) and 0.3g of absorbed water, 24g of 1,8-diazabicyclo [5.4.0] -7-undecene (DBU) was added to prepare a mixed solution. The concentration of cellulose fiber in the mixed solution was 20% by mass and the alkali concentration was 77% by mass. The mixed solution was stirred 10 times for 60 seconds at 2000rpm and 97.9kpa (normal pressure) (the interval time after the end of one stirring was 600 seconds). Then, the cyclic amide compound reaction step and the neutralization step were carried out in the same manner as in Example 4 or 9 to obtain a hydrophobically modified cellulose fiber.

[0093] [evaluate]

[0094] Evaluation of the dispersibility of epoxy resin

[0095] After the above-mentioned aqueous solution preparation step, cyclic amide compound reaction step, neutralization step, etc., suction filtration is performed, and 0.3 g of hydrophobic modified cellulose fiber (or modified cellulose fiber) that has become absolutely dry under heating at 105°C is mixed with 5.7 g of double F-type epoxy resin (835LV: manufactured by DIC Corporation) to make the cellulose fiber concentration in the mixture 5% by mass. Then, stirring / crushing is performed with a spoon for 5 minutes, and stirring is performed for 300 seconds at 2000 rpm and 0.8 kPa with Awatori Rentaro (vacuum type, ARV-310P, manufactured by THINKY Corporation). Evaluation is performed as follows according to the size of the solid content remaining in the obtained composition. Δ~◎ is a range without practical problems.

[0096] ×: A large amount of solid content remained.

[0097] Δ: A small amount of solid content remains.

[0098] ○: A little solid content remains, but the solid content is dispersed when crushed with a spatula.

[0099] ⊚: No solid content was visually confirmed.

[0100] and, Figure 1 to Figure 3 2 shows photographs of compositions (after stirring) obtained by mixing the hydrophobically modified cellulose fibers (or modified cellulose fibers) produced in Examples 1, 3, 4, 8, 11 to 13 and Comparative Examples 1, 3, and 7 with an epoxy resin.

[0101] [Table 1]

[0102]

[0103] [Table 2]

[0104]

[0105]

[0106] As shown in Table 1, Table 2 and Figure 1 to Figure 3 As shown in the above, after mixing cellulose fibers with an alkali, a cyclic amide compound is reacted to obtain hydrophobically modified cellulose fibers having good dispersibility in epoxy resin (Examples 1 to 13). In addition, even if the amount of the cyclic amide compound is relatively small (for example, AGU is 1 or less), the same dispersibility as when a large amount of the cyclic amide compound is used (AGU is 8.17) can be obtained (comparison between Examples 4 and 5, and comparison between Examples 8 and 9 and 10).

[0107] It should be noted that even if a cyclic amide compound is used, the dispersibility cannot be improved when the amount is too small (Comparative Examples 2 and 5). It can be considered that the hydrophobic modification of the cellulose fiber is insufficient. In addition, even when methanol is used instead of the cyclic amide compound, the dispersibility is not improved (Comparative Examples 3 and 6). It can be considered that the reactivity of the hydrophobic modifier is insufficient and the hydrophobic modification cannot be performed. In addition, the dispersibility is not improved at all when the cellulose fiber is treated with alkali only (Comparative Examples 1 and 4). Moreover, when a high concentration of DBU is used as an alkali (Examples 12 and 13), the dispersibility is partially improved. On the other hand, if these Examples 12 and 13 are compared with Examples 4 and 9, the dispersibility is slightly lower. It can be considered that this is because DBU has a relatively large structure compared to NaOH, so it is difficult to capture H+ from the OH group on the surface of the cellulose fiber. Moreover, under the same treatment time, the effect efficiency is expected to be poor.

[0108] B. Evaluation of hydrophobicity

[0109] [Preparation of epoxy resin composition]

[0110] Hydrophobically modified cellulose fibers were prepared in the same manner as in Examples 4, 9, and 11, and the hydrophobically modified cellulose fibers were mixed with an epoxy resin to obtain an epoxy resin composition in the same manner as in the evaluation of the dispersibility of the epoxy resin.

[0111] As a reference example, untreated cellulose fibers (KC Flock W-50GK, manufactured by Nippon Paper Industries) were added to a bis-F type epoxy resin (835LV: manufactured by DIC) so that the cellulose fiber concentration was 5% by mass, and kneaded for 300 seconds at 2000 rpm and 0.8 kPa using Awatori Rentaro (vacuum type, ARV-310P, manufactured by THINKY Co., Ltd.) to prepare an epoxy composition. Kneading was performed at 0.8 kPa for 300 seconds to prepare an epoxy composition.

[0112] [Analysis of hydrophobicity]

[0113] The above four epoxy resin compositions were allowed to stand at room temperature for 12 hours respectively. The viscosity after standing was measured with a cone-plate viscometer (TVE-35H, conical rotor: 3°×R9.7, manufactured by Toki Sangyo Co., Ltd.). At this time, the measured value after 25°C, 50 rpm rotation, and 30 seconds was determined. It should be noted that the smaller the value, the smaller the friction between the epoxy resin and the cellulose fiber, indicating that the hydrophobicity of the cellulose fiber is higher. The results are shown in Table 3 below.

[0114] [Table 3]

[0115]

[0116] As shown in Table 3 above, compared with the case of using unmodified cellulose fibers, the viscosity of the epoxy resin composition using the hydrophobically modified cellulose fibers of Examples 4, 9 and 11 becomes lower. It shows that the affinity of epoxy resin and cellulose fibers is improved by hydrophobic modification. In addition, compared with Example 9 neutralized with hydrochloric acid, the TI value (thixotropic index) measured separately for the hydrophobically modified cellulose fibers of Example 4 neutralized with acetic acid and Example 11 neutralized with CP-MABA solution is low, which inhibits the friction between cellulose fibers. That is, it can be said that the amino group derived from the cyclic amide compound reacts with acetic acid and CP-MABA, reducing the hydrogen bonds of the hydroxyl group and the amino group when treated with hydrochloric acid, and the hydrophobicity is improved. Moreover, compared with Example 4 neutralized with acetic acid, the TI index and viscosity of Example 11 neutralized with CP-MABA solution are low. Therefore, it can be said that by reacting with CP-MABA having an aromatic ring, it is more hydrophobic.

[0117] This application claims the priority based on Japanese Patent Application No. 2022-138431 filed on August 31, 2022. The contents described in the specification and drawings of that application are incorporated herein by reference in their entirety.

[0118] Industrial Applicability

[0119] According to the method for producing hydrophobically modified cellulose fibers of the present invention, hydrophobically modified cellulose fibers can be efficiently produced with a small amount of hydrophobic modifier. In addition, the hydrophobically modified cellulose fibers obtained by the production method have high affinity with resins or organic solvents and can be applied to various composite materials.

Claims

1. A method for producing hydrophobically modified cellulose fibers, the method comprising: A step of mixing cellulose fibers, alkali, and water to prepare an aqueous solution having a cellulose fiber concentration of 0.5 mass % to 50 mass %; A step of adding 0.2 equivalents or more and 10 equivalents or less of a cyclic amide compound to the aqueous solution relative to the amount of anhydroglucose units contained in the cellulose fibers to react the cellulose fibers with the cyclic amide compound; and A step of further adding an acid to the aqueous solution to neutralize the base.

2. The method for producing hydrophobically modified cellulose fibers according to claim 1, wherein: The base is an inorganic base, In the step of preparing the aqueous solution, the concentration of the cellulose fibers is set to 1% by mass or more and 30% by mass or less, and the concentration of the inorganic base is set to 1% by mass or more and 10% by mass or less.

3. The method for producing hydrophobically modified cellulose fibers according to claim 1, wherein: The cyclic amide compound is N-methylpyrrolidone.

4. The method for producing hydrophobically modified cellulose fibers according to claim 2, wherein: The amount of the cyclic amide compound added is 0.7 equivalents or more and 1.0 equivalents or less relative to the amount of the anhydrous glucose unit.

5. The method for producing hydrophobically modified cellulose fibers according to claim 1, wherein: The base is an amine compound.

6. The method for producing hydrophobically modified cellulose fibers according to claim 1, wherein: The acid is an organic acid.

7. A hydrophobically modified cellulose fiber, wherein the hydrophobically modified cellulose fiber is a hydrophobically modified cellulose fiber, wherein: The cellulose constituting the cellulose fiber has a structure in which a cyclic amide compound is ring-opening polymerized on the OH group of the cellulose.

8. The hydrophobically modified cellulose fiber according to claim 7, wherein: The hydrophobically modified cellulose fiber comprises a structure represented by the following chemical formula: [Chemical formula 1] In the chemical formula, Cell represents a residue obtained by removing an OH group from a glucose unit constituting cellulose. X represents a divalent residue obtained by removing a carboxyl group and an amine from the ring-opened form of the cyclic amide compound, R 1 represents hydrogen or an alkyl group having 1 to 6 carbon atoms, R 1 It represents hydrogen or a monovalent group having 1 to 10 carbon atoms.

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