Hydrophobically modified cellulose fibers and method for producing same

Abstract

To provide a method that produces hydrophobically modified cellulose fibers efficiently using little hydrophobic modifier. The method for producing cellulose fibers that solves this problem comprises: a step that mixes cellulose fibers, a base, and water and prepares an aqueous solution having a concentration of cellulose fibers of from 0.5 mass% to 50 mass% and a concentration of base of from 1 mass% to 10 mass%; a step that adds from 0.2 equivalent to 10 equivalents of a cyclic amide compound relative to the anhydrous glucose units contained in the cellulose fibers to the aqueous solution and reacts the cellulose fibers with the cyclic amide compound; and a step that further adds an acid to the aqueous solution and neutralizes the base.

Description

Hydrophobically modified cellulose fiber and its manufacturing method

[0001] The present invention relates to a hydrophobically modified cellulose fiber and a method for producing the same.

[0002] In recent years, research has been conducted into reducing greenhouse gas emissions by combining biomass-derived materials and replacing various conventional composite materials. Cellulose fiber is known as one of the biomass-derived materials. Cellulose fiber has high hydrophilicity due to the OH groups of the glucose units contained in the cellulose molecular structure. However, highly hydrophilic cellulose fiber has low compatibility with organic solvents and resins, making it difficult to use it as is in composite materials.

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

[0004] Japanese Patent Application Laid-Open No. 2020-75950

[0005] However, the method described in Patent Document 1 required a large amount of acetic anhydride for the hydrophobic modification treatment. The reason for this is as follows: Cellulose fibers have the tendency to aggregate when dehydrated. Therefore, the hydrophobic modification treatment is performed by dispersing the cellulose fibers in water. However, when acetic anhydride is added to an aqueous cellulose fiber solution, the acetic anhydride reacts irreversibly with the water to produce acetic acid. In other words, the acetic anhydride is consumed by the water before reacting with the cellulose fibers, and the hydrophobic modification treatment of the cellulose fibers does not proceed sufficiently. Therefore, during the hydrophobic modification treatment, it is necessary to add acetic anhydride to react with all the water present in the system, and acetic anhydride to perform the hydrophobic modification treatment on the cellulose fibers, which requires a large amount of acetic anhydride.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a method for efficiently producing hydrophobically modified cellulose fiber using a small amount of hydrophobic modifier, and hydrophobically modified cellulose fiber obtained by this method.

[0007] The present invention provides a method for producing hydrophobically modified cellulose fiber, which includes the steps of: mixing cellulose fiber, a base, 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; adding a cyclic amide compound to the aqueous solution in an amount of 0.2 equivalents to 10 equivalents relative to the amount of anhydrous glucose units contained in the cellulose fiber to react the cellulose fiber and the cyclic amide compound; and further adding an acid to the aqueous solution to neutralize the base.

[0008] The present invention further provides a hydrophobically modified cellulose fiber, which has a structure in which a cyclic amide compound is ring-opening polymerized to an OH group of cellulose constituting the cellulose fiber.

[0009] According to the method for producing hydrophobically modified cellulose fiber of the present invention, hydrophobically modified cellulose fiber can be produced efficiently using a small amount of hydrophobic modifier. Furthermore, the hydrophobically modified cellulose fiber obtained by this production method has high affinity with resins and organic solvents and is applicable to various composite materials.

[0010] Fig. 1 is a photograph showing the state of compositions in which the hydrophobically modified cellulose fibers obtained in Examples 1, 3, 4, and 8 are dispersed in an epoxy resin. Fig. 2 is a photograph showing the state of compositions in which the (hydrophobically) modified cellulose fibers obtained in Example 11, Comparative Example 1, Comparative Example 3, and Comparative Example 7 are dispersed in an epoxy resin. Fig. 3 is a photograph showing the state of compositions in which the hydrophobically modified cellulose fibers obtained in Examples 12 and 13 are dispersed in an epoxy resin.

[0011] 1. Method for producing hydrophobically modified cellulose fiber The present invention relates to a method for producing hydrophobically modified cellulose fiber, in which cellulose fiber is subjected to a hydrophobically modified treatment to enhance its affinity with various resins and organic solvents.

[0012] As mentioned above, when acetic anhydride is used as a hydrophobic modifier, a large amount of acetic anhydride is required, which poses problems in terms of cost and production efficiency. In contrast, in the production method of the present invention, a cyclic amide compound is used as the hydrophobic modifier. Although the cyclic amide compound reacts with water in the system, the reaction is reversible. Therefore, when hydrophobically modifying cellulose fiber, the hydrophobic modifier (cyclic amide compound) is not consumed by the reaction with water, and efficient treatment can be achieved with a small amount of hydrophobic modifier.

[0013] Specifically, the method for producing hydrophobically modified cellulose fiber of the present invention includes the steps of mixing cellulose fiber, a base, 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"); adding a cyclic amide compound in an amount of 0.2 equivalents to 10 equivalents relative to the amount of anhydrous glucose units contained in the cellulose fiber to the aqueous solution to react the cellulose fiber and the cyclic amide compound (hereinafter also referred to as the "cyclic amide compound reaction step"); and further adding an acid to the aqueous solution to neutralize the base (hereinafter also referred to as the "neutralization step").

[0014] In the method for producing hydrophobically modified cellulose fiber of the present invention, the reaction proceeds as shown in the chemical reaction formula below. In the formula below, Cell represents the residue obtained by removing an OH group from cellulose fiber. Although the chemical reaction formula below shows only one OH group of the cellulose fiber, cellulose fiber has many OH groups on its surface, and in reality, the same reaction occurs with multiple OH groups on the cellulose fiber.

[0015] Furthermore, the OH group represented by the chemical reaction formula below may be any OH group of the glucose unit in the molecular structure of cellulose (fiber). In other words, a glucose unit has three OH groups, and any OH group at any position may react with a cyclic amide compound as shown below. In this reaction, only one OH group in the glucose unit may react with the cyclic amide compound, two OH groups may each react with a cyclic amide compound, or all three OH groups may react with a cyclic amide compound. In the present application, it is considered that the OH group at the 6th position of the glucose unit is particularly likely to react with a cyclic amide compound.

[0016] In the manufacturing method of the present invention, first, in the aqueous solution preparation step, cellulose fiber, a base (NaOH in the chemical reaction formula below), and water are mixed to prepare an aqueous solution containing cellulose fiber and a base. Then, in the cyclic amide compound reaction step, a cyclic amide compound (N-methylpyrrolidone (also referred to as "NMP") in the formula below) is added to the aqueous solution, and the cyclic amide compound is reversibly ring-opened by the base in the system. In addition, the cyclic amide compound and the OH groups (O － Na ＋ Subsequently, in the neutralization step, when an acid (an organic acid (R-COOH, where R- is any organic group) in the chemical reaction formula below) 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 form an amide bond.

[0017] Through the above series of steps, hydrophobic groups are introduced onto the surface of the cellulose fiber, and the cellulose fiber is subjected to a hydrophobic modification treatment. Note that in the neutralization step, it is not necessary to react an acid with an amine derived from a cyclic amide compound; for example, it is also possible to simply neutralize the base in the system with an acid. Each step of the production method is described in detail below.

[0018] (1) Aqueous Solution Preparation Step In the aqueous solution preparation step, cellulose fiber, a base, and water are mixed to prepare an aqueous solution having a cellulose fiber concentration of 0.5% by mass or more and 50% by mass or less.

[0019] The water used in this step is preferably ion-exchanged water in order to suppress side reactions.

[0020] Furthermore, the cellulose fibers used in this process may be fibrous and contain cellulose, and may also contain components other than cellulose, such as hemicellulose or lignin. When components other than cellulose contain hydroxyl groups, such as hemicellulose, the hydroxyl groups may react with the cyclic amide compound. Therefore, when the cellulose fibers contain hemicellulose, it is preferable to adjust (increase) the amount of cyclic amide compound, taking into account the amount of hydroxyl groups contained in the components other than cellulose. From the perspective of efficiently performing the hydrophobic modification treatment, the proportion of cellulose in the cellulose fibers is preferably 30% by mass or more, more preferably 60% by mass or more. The cellulose concentration in the cellulose fibers can be determined by comprehensively evaluating the results of multiple analyses. Specifically, since hemicellulose, lignin, and the like are amorphous, the amount of cellulose in the cellulose fibers can be determined by sugar analysis using X-ray diffraction or ion chromatography.

[0021] The crystallinity of the cellulose fiber is preferably 50% or more, more preferably 60% or more. When the resulting hydrophobically modified cellulose fiber is used in various composite materials, the mechanical strength of the composite material is likely to be increased. The crystallinity is expressed as (crystalline region of cellulose) / {(crystalline region of cellulose)+(amorphous region of cellulose)+(non-cellulose-derived region (amorphous region))}×100, and can be determined by X-ray diffraction, as described above. The Segal method is known as a more specific calculation method.

[0022] The raw material for the cellulose fiber is not particularly limited, and examples of raw materials include pulp obtained from wood, bamboo, hemp, jute, kenaf, cotton, beet, agricultural waste, cloth, etc.; and recycled materials such as rayon and cellophane. The pulp may also be chemical pulp obtained by chemically or mechanically treating plant materials. Specifically, any pulp may be used, such as sulfite pulp, semi-chemical pulp, chemi-ground pulp, chemi-mechanical pulp, groundwood pulp, refiner mechanical pulp, thermo-mechanical pulp, chemi-thermomechanical pulp, deinked waste paper pulp, recycled corrugated paper pulp, or recycled magazine paper pulp. The cellulose fiber referred to in this specification includes not only completely fibrous cellulose but also, for example, cellulose fibers rolled into particles or processed or molded into any shape.

[0023] The average fiber diameter of the cellulose fiber usable in this step is 0.02 μm or more, preferably 1 μm to 100 μm, and more preferably 5 μm to 60 μm. When the average fiber diameter of the cellulose fiber is 1 μm to 100 μm, it is inexpensive and easy to handle. Furthermore, the average fiber length is preferably 100 μm to 10,000 μm, and more preferably 200 μm to 5,000 μm. When the average fiber length of the cellulose fiber is within the above range, the resulting hydrophobically modified cellulose fiber can be easily used for various applications.

[0024] The above average fiber diameter and fiber length vary depending on the diameter measured, but are average values ​​obtained by observing the morphology using an optical microscope, electron microscope, AFM, etc. and measuring the fiber diameter and fiber length of 100 or more cellulose fibers.

[0025] The base may be any compound capable of ring-opening the cyclic amide compound and promoting the reaction between the OH groups of the cellulose fiber and the ring-opened form of the cyclic amide compound in the cyclic amide compound reaction step described below. The base is preferably a compound capable of adjusting the pH of the aqueous solution to 11 or higher. A pH of 11 or higher of the aqueous solution facilitates the promotion of the reaction. Examples of bases used in this step include inorganic bases such as alkali metal hydroxides and alkaline earth metal hydroxides; and organic bases such as amine compounds. Specific examples of inorganic bases such as alkali metal hydroxides and alkaline earth metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, and barium hydroxide. Examples of organic bases such as amine compounds include tertiary amine compounds such as triethylamine, diazabicycloundecene, and diazabicyclononene. These may be used alone or in combination in this step. Among these, sodium hydroxide and trimethylamine are preferred from the viewpoint of low cost and ability to treat cellulose fibers quickly, and diazabicycloundecene and diazabicyclononene are more preferred from the viewpoint of allowing the reaction to proceed gently.

[0026] Here, the method for mixing the cellulose fiber, base, and water in the aqueous solution preparation step is not particularly limited, but a mixing method that does not change the crystalline structure of cellulose is preferred. When cellulose fiber comes into contact with an aqueous solution with a high base concentration, the crystalline structure of cellulose may change. Therefore, in this step, it is preferable to prepare a solution in which cellulose fiber is dispersed in water and a solution in which a base is dispersed in water, and then mix these solutions.

[0027] The cellulose fiber concentration in the aqueous solution prepared in this step may be from 0.5% by mass to 50% by mass, preferably from 1% by mass to 30% by mass. When the cellulose fiber concentration in the aqueous solution is 0.5% by mass or more, the cellulose fiber can be efficiently hydrophobically modified. On the other hand, if the cellulose fiber concentration is too high, the viscosity of the aqueous solution increases and becomes difficult to handle. However, when the cellulose fiber concentration is 50% by mass or less, the viscosity of the aqueous solution can be kept within the desired range.

[0028] Furthermore, when an inorganic base such as an alkali metal hydroxide or an alkaline earth metal hydroxide is used as the base, the concentration of the inorganic base in 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. When the concentration of the inorganic base is 1% by mass or more, the cyclic amide compound and the cellulose fiber are more likely to react in the cyclic amide compound reaction step described below. On the other hand, when the concentration of the inorganic base is 10% by mass or less, the crystalline structure of cellulose is less likely to be affected. On the other hand, when the above-mentioned amine compound is used as the base, the amount of base (amine compound) added is appropriately selected depending on the type, etc., and may be an amount that can adjust the pH of the aqueous solution to 11 or more, as described above.

[0029] In this step, it is preferable to thoroughly stir the cellulose fiber, base, and water after mixing them. The stirring time and stirring method are appropriately selected depending on the amount and viscosity (concentration of cellulose fiber) of the aqueous solution. If heat is generated during mixing, the crystalline structure of cellulose may change or the cellulose may easily decompose. Therefore, when mixing, it is preferable to stir the mixture in multiple batches with intervals between each batch, or to stir the mixture in small amounts at a time.

[0030] After mixing the cellulose fiber, the base, and the water, the aqueous solution may be concentrated as needed. The concentration method is not limited, and filtration is an example. In this case, it is preferable to adjust the concentration amount so that the cellulose fiber concentration in the concentrated aqueous solution is 0.5% by mass or more and 50% by mass or less, preferably 1% by mass or more and 30% by mass or less.

[0031] (2) Cyclic Amide Compound Reaction Step The cyclic amide compound reaction step is a step in which a predetermined amount of a cyclic amide compound is added to the aqueous solution to react the cellulose fiber with the cyclic amide compound.

[0032] The cyclic amide compound may be any compound having a cyclic structure and an amide bond, i.e., an -NHCO- structure, in the cyclic portion, which undergoes ring-opening in the presence of a base to form an ester bond with the OH groups 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-dimethylpropyleneurea, 1,3-dimethyl-2-imidazolidinoic acid, and various other lactams. These compounds may be used alone or in combination of two or more. Among these, N-methyl-2-pyrrolidone is preferred due to its good reactivity and easy availability. N-methyl-2-pyrrolidone is also suitable because it does not react with the OH groups inside the crystalline structure of cellulose fibers (to maintain the crystalline structure) and has a molecular size similar to that of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical), which is known to react with the OH groups on the surface of cellulose fibers.

[0033] The amount of cyclic amide compound added to the aqueous solution in this step may be an amount such that the equivalent weight (AGU) relative to the amount of anhydroglucose units of the cellulose fiber in the aqueous solution is 0.2 to 10, preferably 0.7 to 10, and more preferably 0.7 to 1.0. An AGU of 0.2 or greater ensures sufficient hydrophobic modification of the cellulose fiber. An AGU of 0.7 or greater can produce hydrophobically modified cellulose fiber with higher affinity for resins and organic solvents. On the other hand, an AGU of 10 or less can reduce the amount of excess cyclic amide compound remaining in the system. An AGU of 1.0 or less can efficiently produce hydrophobically modified cellulose fiber with a small amount of hydrophobic modifier. The amount of anhydroglucose units contained in the cellulose fiber is calculated from the mass of the cellulose fiber in the aqueous solution. When the cellulose fiber is wood flour, lignocellulose, or the like and contains lignin, the amount of lignin is excluded from the mass of the cellulose fiber for calculation.

[0034] In this step, after the addition of the cyclic amide compound, the aqueous solution is preferably stirred to allow the cyclic amide compound and the cellulose fiber to react sufficiently. The temperature of the aqueous solution at this time is preferably 5°C or higher and 90°C or lower, more preferably 10°C or higher and 60°C or lower. The stirring time and stirring method are appropriately selected depending on the amount and viscosity of the aqueous solution, etc. When stirring, in order to prevent changes in the crystalline structure of cellulose or decomposition of cellulose due to heat generated by stirring or base in the system, it is preferable to cool the stirring vessel using a refrigerant or the like or to stir in multiple batches while providing intervals.

[0035] (3) Neutralization Step In the neutralization step, an acid is added to the aqueous solution to neutralize the base. In addition to neutralizing the base, this step may also involve reacting the acid with the amino group derived from the cyclic amide compound.

[0036] The type of acid used in this step is not particularly limited and may be, for example, an inorganic acid such as hydrochloric acid, or an organic acid, although an organic acid is preferred. When an organic acid is used as the acid, the organic acid reacts with the amino group derived from the cyclic amide compound to form an amide bond. As a result, the organic chains present on the surface of the cellulose fiber become longer, further increasing the hydrophobicity of the resulting hydrophobically modified cellulose fiber.

[0037] 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 carboxyalkylamino group-containing compounds having an aromatic ring represented by the following chemical formula (hereinafter also referred to as "CP-MABA"). Of these, acetic acid and CP-MABA are preferred in terms of availability and other factors. In the above formula, X represents an alkali metal atom or a hydrogen atom.

[0038] The amount of acid used is appropriately selected depending on the amount of the base, and may be added until the aqueous solution becomes neutral.

[0039] After the addition of the acid, the hydrophobically modified cellulose fiber may be further washed and dried, if necessary.

[0040] 2. Hydrophobically Modified Cellulose Fiber The present invention also provides hydrophobically modified cellulose fibers produced by the above-described method, i.e., hydrophobically modified cellulose fibers containing structures formed by ring-opening polymerization of the above-described cyclic amide compounds with OH groups of cellulose (fiber). In the hydrophobically modified cellulose fibers, the amine terminals formed by ring-opening of the above-described cyclic amide compounds may remain as they are, or a structure derived from the above-described organic acid may be further bonded to the amines.

[0041] The hydrophobically modified cellulose fiber has, for example, the following structure: In the above general formula, Cell represents a residue obtained by removing an OH group from a glucose unit constituting cellulose. Furthermore, X represents a divalent residue obtained by removing a carboxy group and an amine from the ring-opened product of the cyclic amide compound described above, and is preferably an alkylene group having 2 to 6 carbon atoms. １ represents hydrogen or an alkyl group having 1 to 6 carbon atoms, and is preferably hydrogen or a methyl group. ２ represents hydrogen or a monovalent group having 1 to 10 carbon atoms. ２ R may contain a carboxy group, a carbonyl group, an amino group, a halogen group, an aromatic group, an alkyl group, or the like in its structure. ２ Specific examples of include groups derived from organic acids explained in the above production method, and preferred are a methyl group and a chlorophenylmethylaminobutyl group.

[0042] Here, cellulose (fiber) contains many OH groups in its molecular structure, but it is not necessary for all OH groups to undergo ring-opening polymerization of the above-mentioned cyclic amide compound. It is sufficient that at least some of the OH groups contain a structure resulting from ring-opening polymerization of the above-mentioned cyclic amide compound. This structure can be identified, for example, by analysis such as NMR. Furthermore, the amount of the structure resulting from ring-opening polymerization of the cyclic amide compound contained in the hydrophobically modified cellulose fiber may be an amount that provides affinity with the target resin, organic solvent, etc., and does not affect the crystalline structure of the cellulose, and is selected appropriately depending on the type of these resins and organic solvents.

[0043] The hydrophobically modified cellulose fiber of the present invention has a high affinity with various resins and organic solvents because the hydrophobic group represented by the above formula is bonded to the cellulose fiber. Therefore, it can be easily mixed with thermosetting resins, thermoplastic resins, and organic solvents to form composite materials. Such composite materials can be used in a variety of applications, such as electrical appliances, building materials, vehicles such as automobiles and trains, and aircraft.

[0044] The present invention will be further described below with reference to examples and comparative examples, but the technical scope of the present invention is not limited thereto.

[0045] A. Evaluation of Dispersibility of Cellulose Fiber [Example 1] (1) Aqueous Solution Preparation Step (Preparation of Base-Containing Cellulose Fiber Aqueous Solution) 20 g (bone-dry mass) of cellulose fiber (KC Flock W-50GK, manufactured by Nippon Paper Industries Co., Ltd.) with an absolute dryness of 95.1% was immersed in 86 g of ion-exchanged water. Furthermore, 32 g of sodium hydroxide and 262 g of ion-exchanged water were mixed to prepare a basic aqueous solution. These were then mixed to obtain an aqueous solution with a cellulose fiber concentration of 5 mass% and a base (NaOH) concentration of 8 mass%. 100 g of the obtained aqueous solution was separated, and each aqueous solution was stirred three times for 200 seconds each (with a 600-second interval after each stirring) using a Thinky Mixer (vacuum type, ARV-310P, manufactured by Thinky Corporation) at 2000 rpm and 97.9 kPa (normal pressure). The mixed aqueous solution after stirring was suction-filtered, and the filtrate was used as a base-containing cellulose fiber aqueous solution. The solid content (base-containing cellulose fiber) concentration of the base-containing cellulose fiber aqueous solution calculated from the mass of the filtrate was 18.5% by mass, and when a portion was dropped onto pH test paper, the pH was 11 or higher.

[0046] (2) Cyclic Amide Compound Reaction Step 0.29 g of N-methylpyrrolidone (NMP, a cyclic amide compound) was added to 10.8 g of the base-containing cellulose fiber aqueous solution prepared in the above step (amount of base-containing cellulose fiber: 2 g). The amount of NMP corresponded to an equivalent of 0.24 anhydroglucose units (AGU) in the cellulose fiber. The mixture was then stirred six times for 60 seconds each (with an interval of 600 seconds after each stirring) using a THINKY MIXER (vacuum type, ARV-310P, manufactured by THINKY CORPORATION) at 2000 rpm and 97.9 kPa (normal pressure).

[0047] (3) Neutralization step: 20 g of ion-exchanged water was added to the stirred aqueous solution, and then a 10% by mass aqueous acetic acid solution was added until the aqueous solution became neutral. 100 g of ion-exchanged water was added to the neutralized aqueous solution, and the mixture was subjected to suction filtration. Subsequently, the suction was stopped, and 100 g of ion-exchanged water was added, and the mixture was subjected to suction filtration again. This process was repeated nine times to thoroughly wash the mixture and dehydrate it. The dehydrated mixture was heated at 105°C for 3 hours, and bone-dry hydrophobically modified cellulose fiber was obtained.

[0048] Examples 2 to 5 Hydrophobically modified cellulose fibers were obtained in the same manner as in Example 1, except that the amount of NMP (AGU) added in the reaction step of the cyclic amide compound was changed to the value shown in Table 1.

[0049] Examples 6 to 10 Hydrophobically modified cellulose fibers were obtained in the same manner as in Examples 1 to 5, except that the acid used in the neutralization step was changed to 10% by mass hydrochloric acid.

[0050] Example 11 Hydrophobically modified cellulose fiber was obtained in the same manner as in Example 4, except that the acid in the neutralization step was the above-mentioned CP-MABA solution (chlorophenylmethylaminobutanoic acid (CPMABA) as the organic acid). CP-MABA was prepared as follows.

[0051] Preparation of CP-MABA solution The distillation residue of the washing wastewater from the polyphenylene sulfide (PPS) polymerization reaction product was adjusted to approximately pH 1 with hydrochloric acid to precipitate the oligomer, resulting in solid-liquid separation. Caustic soda was then added to the filtrate until the pH was approximately 4, yielding a CP-MABA solution (brown oil) with a CP-MABA content of 80.7%. The resulting CP-MABA solution was used as the organic acid. Purity was analyzed by high-performance liquid chromatography (HPLC).

[0052] Comparative Examples 1 and 4 Modified cellulose fibers were obtained in the same manner as in Example 1 or 6, except that the reaction step with the cyclic amide compound was not carried out.

[0053] Comparative Examples 2 and 5 Hydrophobically modified cellulose fibers were obtained in the same manner as in Example 1 or 6, except that the amount (AGU) of NMP added in the reaction step of the cyclic amide compound was changed to the value shown in Table 1.

[0054] Comparative Examples 3 and 6 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.

[0055] Comparative Example 7 A mixture was prepared by adding 24 g of 1,8-diazabicyclo[5.4.0]-7-undecene (also referred to as "DBU") to 6 g (bone dry weight) of cellulose fiber (KC Flock W-50GK, manufactured by Nippon Paper Industries Co., Ltd.) and 0.3 g of absorbed water. The cellulose fiber concentration in the mixture was 20% by mass, and the base concentration was 77% by mass. The mixture was stirred 10 times for 60 seconds each (with an interval of 600 seconds after each stirring) in a mixer (vacuum type, ARV-310P, manufactured by Thinky Corporation) at 2000 rpm and 97.9 kPa (normal pressure). The mixture after stirring was neutralized in the same manner as in Example 4, to obtain hydrophobically modified cellulose fiber.

[0056] Examples 12 and 13 A mixture was prepared by adding 24 g of 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) to 6 g (bone dry weight) of cellulose fiber (KC Flock W-50GK, manufactured by Nippon Paper Industries Co., Ltd.) and 0.3 g of absorbed water. The cellulose fiber concentration in the mixture was 20% by mass, and the base concentration was 77% by mass. The mixture was stirred 10 times for 60 seconds each (with an interval of 600 seconds after each stirring) in a mixer (vacuum type, ARV-310P, manufactured by Thinky Corporation) at 2000 rpm and 97.9 kPa (normal pressure). Thereafter, a cyclic amide compound reaction step and a neutralization step were carried out in the same manner as in Examples 4 and 9, to obtain hydrophobically modified cellulose fiber.

[0057] [Evaluation] Evaluation of dispersibility in epoxy resin After the above-mentioned aqueous solution preparation step, cyclic amide compound reaction step, neutralization step, etc., were performed, 0.3 g of hydrophobically modified cellulose fiber (or modified cellulose fiber) that had been dried by heating at 105°C was mixed with 5.7 g of Bis-F type epoxy resin (835LV: manufactured by DIC Corporation) to adjust the cellulose fiber concentration in the mixture to 5% by mass. The mixture was then stirred / pulverized with a medicine spoon for 5 minutes, and then stirred for 300 seconds at 2000 rpm and 0.8 kPa using a Thinky Mixer (vacuum type, ARV-310P, manufactured by Thinky Corporation). The size of the solids remaining in the resulting composition was evaluated as follows: △ to ⊚ indicates a range that is acceptable for practical use. ×: A large amount of solids remained. △: A small amount of solids remained. ◯: A small amount of solids remained, but the solids dispersed when crushed with a medicine spoon. ◎: No solids were visible. Figures 1 to 3 also show photographs of compositions (after stirring) in which 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 were mixed with epoxy resin.

[0058]

[0059]

[0060] As shown in Tables 1 and 2 and Figures 1 to 3, hydrophobically modified cellulose fibers with good dispersibility in epoxy resins were obtained by mixing cellulose fibers with a base and then reacting them with a cyclic amide compound (Examples 1 to 13). Furthermore, even when the amount of cyclic amide compound was relatively small (e.g., AGU of 1 or less), dispersibility equivalent to that obtained when a large amount of cyclic amide compound was used (AGU of 8.17) was obtained (Compare Examples 4 and 5, and Examples 8 and 9 and 10).

[0061] Even when a cyclic amide compound was used, dispersibility could not be improved if the amount was too small (Comparative Examples 2 and 5). This is thought to be due to insufficient hydrophobic modification of the cellulose fiber. Furthermore, dispersibility did not improve when methanol was used instead of the cyclic amide compound (Comparative Examples 3 and 6). It is thought that the reactivity of the hydrophobic modifier was insufficient, preventing hydrophobic modification. Furthermore, simply treating the cellulose fiber with a base did not improve dispersibility at all (Comparative Examples 1 and 4). Furthermore, when a high concentration of DBU was used as the base (Examples 12 and 13), dispersibility was partially improved. However, when Examples 12 and 13 were compared with Examples 4 and 9, the dispersibility was slightly lower. This is thought to be due to the fact that DBU has a relatively bulky structure compared to NaOH, making it difficult to abstract H+ from the OH groups on the cellulose fiber surface. Therefore, it is expected that the efficiency of the treatment was poor for the same treatment time.

[0062] B. Evaluation of Hydrophobicity [Preparation of Epoxy Resin Compositions] Hydrophobically modified cellulose fibers were prepared in the same manner as in Examples 4, 9, and 11 above, and these were mixed with epoxy resins in the same manner as in the evaluation of dispersibility in epoxy resins to obtain epoxy resin compositions. Furthermore, as a reference example, untreated cellulose fiber (KC Flock W-50GK, manufactured by Nippon Paper Industries Co., Ltd.) was added to a bis-F type epoxy resin (835LV, manufactured by DIC) so that the cellulose fiber concentration was 5% by mass, and the mixture was kneaded at 2000 rpm, 0.8 kPa, and for 300 seconds in a THINKY MIXER (vacuum type, ARV-310P, manufactured by THINKY CORPORATION) to prepare an epoxy composition.

[0063] [Analysis of Hydrophobicity] Each of the four epoxy resin compositions described above was allowed to stand at room temperature for 12 hours. The viscosity after standing was measured using a cone-plate viscometer (TVE-35H, cone rotor: 3° x R9.7, manufactured by Toki Sangyo Co., Ltd.). The measured value was determined after 30 seconds at 25°C and 50 rpm rotation. A smaller value indicates less friction between the epoxy resin and the cellulose fiber, and a higher hydrophobicity of the cellulose fiber. The results are shown in Table 3 below.

[0064]

[0065] As shown in Table 3 above, the epoxy resin compositions using the hydrophobically modified cellulose fibers of Examples 4, 9, and 11 had lower viscosities than those using unmodified cellulose fibers. It is clear that the hydrophobically modified cellulose fibers of Examples 4, 9, and 11 exhibited increased affinity for the epoxy resin. Furthermore, the separately measured thixotropy index (TI) values ​​were lower for the hydrophobically modified cellulose fibers of Example 4 (neutralized with acetic acid) and Example 11 (neutralized with CP-MABA solution) than for Example 9 (neutralized with hydrochloric acid), demonstrating reduced friction between the cellulose fibers. In other words, the reaction of the amino groups derived from the cyclic amide compound with acetic acid or CP-MABA reduced the hydrogen bonds derived from the hydroxyl groups in the untreated sample and the amino groups in the hydrochloric acid treatment, resulting in a higher degree of hydrophobicity. Furthermore, Example 11 (neutralized with CP-MABA solution) had lower TI values ​​and viscosities than Example 4 (neutralized with acetic acid). Therefore, it can be said that the reaction with CP-MABA, which has an aromatic ring, enhanced hydrophobicity.

[0066] This application claims priority based on Japanese Patent Application No. 2022-138431, filed August 31, 2022. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety.

[0067] According to the method for producing hydrophobically modified cellulose fiber of the present invention, hydrophobically modified cellulose fiber can be produced efficiently using a small amount of hydrophobic modifier. Furthermore, the hydrophobically modified cellulose fiber obtained by this production method has high affinity with resins and organic solvents and is applicable to various composite materials.

Claims

1. A step of mixing cellulose fiber, a base, 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; 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 fiber to the aqueous solution, and reacting the cellulose fiber with the cyclic amide compound; further adding an acid to the aqueous solution to neutralize the base; A method for producing hydrophobically modified cellulose fiber, comprising the steps of:

2. the base is an inorganic base, In the step of preparing the aqueous solution, the concentration of the cellulose fiber 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. A method for producing the hydrophobically modified cellulose fiber according to claim 1.

3. The cyclic amide compound is N-methylpyrrolidone. A method for producing the hydrophobically modified cellulose fiber according to claim 1.

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

5. The base is an amine compound. A method for producing the hydrophobically modified cellulose fiber according to claim 1.

6. The acid is an organic acid. A method for producing the hydrophobically modified cellulose fiber according to claim 1.

7. A hydrophobically modified cellulose fiber, The compound includes a structure represented by the following chemical formula: 【Chemistry 1】 (In the above 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 carboxy group and an amine from a ring-opened form of a cyclic amide compound; R 1 represents hydrogen or an alkyl group having from 1 to 6 carbon atoms; R 2 represents hydrogen or a monovalent group having 1 to 10 carbon atoms. Hydrophobically modified cellulose fiber.

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