Modified cellulose nanofibers
By modifying cellulose nanofibers with a silane coupling agent containing epoxy groups, the hydrophobicity and dispersion properties are enhanced, addressing the limitations of existing cellulose nanofibers in hydrophobic materials and expanding their application range.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- FUJIKURA COMPOSITES INC
- Filing Date
- 2020-12-28
- Publication Date
- 2026-07-09
AI Technical Summary
Existing cellulose nanofibers face challenges in achieving uniform dispersion in hydrophobic materials due to their hydrophilic nature, limiting their application range and requiring complex modification processes that alter their molecular structure.
Modified cellulose nanofibers are produced by chemically bonding a silane coupling agent with epoxy groups to the hydroxyl groups of cellulose, enhancing hydrophobicity and affinity for hydrophobic substances, allowing uniform dispersion and further modification possibilities.
The modified cellulose nanofibers exhibit excellent hydrophobicity and affinity for hydrophobic materials, enabling uniform dispersion and maintaining high strength, thus expanding their application range and functionality as reinforcing materials.
Smart Images
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Abstract
Description
[Technical Field]
[0001] The present invention relates to modified nanocellulose modified with a silane coupling agent, and more particularly to modified cellulose nanofibers that exhibit affinity for hydrophobic substances. [Background technology]
[0002] Nanocellulose is a cellulose fiber with a thickness on the order of nanometers, obtained by defibrating plant fibers such as pulp in an aqueous medium. Nanocellulose is classified into cellulose nanofibers, cellulose crystals, cellulose whiskers, and bacterial nanocellulose depending on the structure of the cellulose. Due to its lightweight and high strength, cellulose nanofibers are attracting attention for their use as a reinforcing material for thermoplastic resins, for example (see, for example, Patent Document 1).
[0003] On the other hand, because cellulose nanofibers are hydrophilic, uniform dispersion in organic solvents and uniform mixing with hydrophobic materials such as resins are difficult, which limits their range of application. Therefore, for example, a technique has been proposed to impart hydrophobicity to cellulose nanofibers by reacting them with organic vinyl acid and then recovering the product (see, for example, Patent Document 2). Hereinafter, cellulose nanofibers that have been given desired properties such as hydrophobicity from naturally derived cellulose nanofibers obtained from plant fibers, etc., may be referred to as modified cellulose nanofibers.
[0004] However, the modified cellulose nanofibers shown in Patent Document 2 have strict reaction conditions between cellulose nanofibers and vinyl organic acid, and the production process is complicated. Furthermore, in cellulose nanofibers modified with vinyl organic acid, the molecular structure of the cellulose nanofibers themselves changes depending on the degree of modification, leaving room for improvement in terms of improving the hydrophobicity of the cellulose nanofibers.
[0005] Furthermore, as a technique for imparting hydrophobicity to cellulose nanofibers, it has been proposed to modify cellulose nanofibers to be hydrophobic with a small mass of modifying groups by bonding two types of modifying groups to the surface of the cellulose nanofibers: one modified group selected for its wettability, such as aromatic groups, and another modified group selected for its steric repulsion and hydrophobicity, such as polyalkylene glycol groups. However, modified cellulose nanofibers using two types of modifying groups, such as aromatic groups and polyalkylene glycol groups, have a complex chemical structure, and there is still room for improvement in enhancing hydrophobicity. In addition, modified cellulose nanofibers using two types of modifying groups, such as aromatic groups and polyalkylene glycol groups, do not have functional groups with excellent reactivity, which makes it difficult to expand their application fields. [Prior art documents] [Patent Documents]
[0006] [Patent Document 1] Japanese Patent Publication No. 2016-11392 [Patent Document 2] International Publication No. 2016 / 010016 [Overview of the Initiative] [Problems that the invention aims to solve]
[0007] In view of the above circumstances, the present invention aims to provide modified cellulose nanofibers that can easily expand the range of applications of cellulose, are given excellent hydrophobicity, and have excellent affinity with hydrophobic substances. [Means for solving the problem]
[0008] The gist of the present invention is as follows: [1] Modified cellulose nanofibers in which at least some of the hydroxyl groups of cellulose are modified with a silane coupling agent having epoxy groups. [2] The modified cellulose nanofiber according to [1], wherein the silane coupling agent has at least an epoxy group and an alkoxy group. [3] The silane coupling agent is the modified cellulose nanofiber according to [1] or [2] having an epoxy group, an alkoxy group, and an alkyl group. [4] The silane coupling agent is represented by the following general formula (1) [Chemical formula] (In general formula (1), X represents an organic functional group containing an epoxy group, and R 1 , R 2 , R 3 each independently represents chloride, an alkoxy group having 1 to 5 carbon atoms, or an alkyl group having 1 to 5 carbon atoms.) The modified cellulose nanofiber according to any one of [1] to [3]. [5] Among the above R 1 , the above R 2 , the above R 3 , at least one is an alkoxy group having 1 to 5 carbon atoms, and at least one is an alkyl group having 1 to 5 carbon atoms. The modified cellulose nanofiber according to [4]. [6] The silane coupling agent is the modified cellulose nanofiber according to any one of [1] to [5] containing 3-glycidoxypropyl(dimethoxy)methylsilane. [7] The modified cellulose nanofiber according to any one of [1] to [6], which is modified at a charging ratio of the silane coupling agent of 0.001 mol or more and 6.0 mol or less per 1.0 mol of the β-glucose unit of the cellulose. [8] The modified cellulose nanofiber according to any one of [1] to [7], having an average fiber length of 20 μm or more and 200 μm or less, and an average fiber diameter of 4 nm or more and 100 nm or less.
[0009] [1] Modified cellulose nanofibers are modified by chemical bonding of the silane coupling agent to the hydroxyl groups of cellulose. In other words, modified cellulose nanofibers have a structure in which the silane coupling agent is chemically bonded to the hydroxyl groups of cellulose. Note that "cellulose nanofiber" refers to cellulose fiber with an average fiber diameter of less than 1.0 μm, that is, an average fiber diameter on the nanoscale. [Effects of the Invention]
[0010] According to the modified cellulose nanofibers of the present invention, at least a portion of the hydroxyl groups of cellulose are modified with a silane coupling agent having epoxy groups, thereby imparting excellent hydrophobicity and superior affinity to hydrophobic substances. Therefore, the modified cellulose nanofibers of the present invention can be uniformly dispersed in hydrophobic materials such as organic solvents and resins, thereby expanding the range of applications for cellulose nanofibers and reliably imparting the properties of cellulose nanofibers to the target material.
[0011] Furthermore, since the modified cellulose nanofibers of the present invention have highly reactive epoxy groups as functional groups, the modified cellulose nanofibers can be further modified via the epoxy groups. Therefore, the range of hydrophobic substances to which the modified cellulose nanofibers of the present invention can be applied can be easily expanded.
[0012] According to the modified cellulose nanofibers of the present invention, the silane coupling agent has at least an epoxy group and an alkoxy group, thereby reliably modifying the cellulose and reliably imparting excellent hydrophobicity to the modified cellulose nanofibers.
[0013] According to the modified cellulose nanofibers of the present invention, the silane coupling agent has an epoxy group, an alkoxy group, and an alkyl group, so that the cellulose can be reliably modified to surely impart excellent hydrophobicity, and the aggregation of the modified cellulose nanofibers can be surely suppressed. Therefore, the dispersion in hydrophobic substances such as organic solvents and resins can be made more uniform with certainty.
[0014] According to the modified cellulose nanofibers of the present invention, the silane coupling agent has the following general formula (1)
Chemical formula
[0015] According to the modified cellulose nanofibers of the present invention, since the silane coupling agent contains 3-glycidoxypropyl(dimethoxy)methylsilane, while surely imparting more excellent hydrophobicity, the aggregation of the modified cellulose nanofibers can be more surely suppressed.
[0016] According to the modified cellulose nanofibers of the present invention, by being modified at a charging ratio of the silane coupling agent of 0.001 mol or more and 3.0 mol or less per 1.0 mol of the β-glucose unit of cellulose, excellent hydrophobicity can be surely imparted to the modified cellulose nanofibers.
Brief description of the drawings
[0017] [Figure 1](a) is a photograph showing the dispersion state of the dispersion sample immediately after preparation of the dispersion using tetrahydrofuran (THF) as the dispersion solvent in Example 1, (b) is a photograph showing the dispersion state of the dispersion sample immediately after preparation of the dispersion using tetrahydrofuran as the dispersion solvent in Example 2, and (c) is a photograph showing the dispersion state immediately after preparation of the dispersion sample using tetrahydrofuran as the dispersion solvent in Comparative Example 1. [Modes for carrying out the invention]
[0018] The modified cellulose nanofibers of the present invention are such that at least a portion of the hydroxyl groups of cellulose are modified with a silane coupling agent having epoxy groups. In other words, the modified cellulose nanofibers of the present invention are cellulose nanofibers modified with a silane coupling agent.
[0019] The modified cellulose nanofibers of the present invention possess excellent hydrophobicity and exhibit superior affinity for hydrophobic substances. Therefore, the modified cellulose nanofibers of the present invention can uniformly disperse in hydrophobic materials such as organic solvents and resins, thereby expanding the range of applications for cellulose nanofibers and reliably imparting the properties of cellulose nanofibers to the target material such as resin. Furthermore, since the modified cellulose nanofibers of the present invention have highly reactive epoxy groups as functional groups, further modification is possible via these epoxy groups. Therefore, by appropriately selecting the compound to be bonded to the epoxy groups, the range of hydrophobic substances to which the modified cellulose nanofibers of the present invention can be applied can be easily expanded.
[0020] <Cellulose> The cellulose forming the backbone of the modified cellulose nanofibers of the present invention will be described in detail below. In the modified cellulose nanofibers of the present invention, the size of the cellulose is not particularly limited as long as the average fiber diameter is less than 1.0 μm. However, from the viewpoint of homogenizing the cellulose modification sites by the silane coupling agent and expanding the range of application of the modified cellulose nanofibers, the average fiber diameter is preferably 4 nm to 100 nm, and particularly preferably 10 nm to 50 nm. Similarly, the average fiber length of the cellulose is not particularly limited, but from the viewpoint of homogenizing the cellulose modification sites by the silane coupling agent and expanding the range of application of the modified cellulose nanofibers, it is preferably 20 μm to 200 μm, and particularly preferably 50 μm to 150 μm. The average fiber diameter and average fiber length of the cellulose can be measured, for example, by scanning probe microscopy or nitrogen adsorption method for the average fiber diameter, and by electron microscopy (transmission electron microscope (TEM), scanning electron microscope (SEM)) or scanning probe microscopy for the average fiber length.
[0021] Examples of cellulose include cellulose derived from natural products. Specifically, examples of cellulose include cellulose precursors derived from natural products that have been subjected to defibration treatment to form nanofibers. Examples of cellulose precursors that serve as raw materials for cellulose include plant fibers such as pulp.
[0022] <Silane coupling agent> A silane coupling agent is a compound having a functional group and a hydrolyzable silyl group within a single molecule, which reacts with water to convert the hydrolyzable silyl group into a silanol group. The silane coupling agent has substituents for modifying the hydroxyl groups of cellulose that constitute the cellulose nanofiber. In the modified cellulose nanofiber of the present invention, the silane coupling agent must have an epoxy group as a functional group. The silanol group of the silane coupling agent chemically bonds with the hydroxyl groups of cellulose that constitute the cellulose nanofiber, thereby modifying the hydroxyl groups of cellulose. The cellulose is modified by the silane coupling agent when the silanol group, which is produced by the hydrolysis of the hydrolyzable silyl group of the silane coupling agent, chemically bonds with the hydroxyl groups of cellulose.
[0023] As the hydrolyzable silyl group of the silane coupling agent, an alkoxy group is preferred because it can reliably modify cellulose and reliably impart excellent hydrophobicity to modified cellulose nanofibers. In other words, an organosilicon compound having at least an epoxy group and an alkoxy group is preferred as the silane coupling agent.
[0024] The hydrolyzable silyl group of the silane coupling agent is more preferably one having an alkoxy group and an alkyl group, as this reliably modifies cellulose to impart excellent hydrophobicity while reliably suppressing aggregation of modified cellulose nanofibers via the silane coupling agent. In other words, an organosilicon compound having at least an epoxy group, an alkoxy group, and an alkyl group is more preferable as the silane coupling agent. By reliably suppressing aggregation of modified cellulose nanofibers, dispersion in hydrophobic substances such as organic solvents and resins can be more reliably and uniformly achieved.
[0025] As a silane coupling agent, for example, the following general formula (1) is used because it reliably improves the hydrophobicity of modified cellulose nanofibers. [ka] (In general formula (1), X represents an organic functional group containing an epoxy group, and R 1 , R 2 , R 3 Each of these independently represents a chloride, an alkoxy group having 1 to 5 carbon atoms, or an alkyl group having 1 to 5 carbon atoms. Compounds represented by ) are preferred. In compounds of general formula (1), R 1 , R 2 , R 3 A hydrolyzable silyl group is formed by a chemical bond between it and Si.
[0026] R in compounds of general formula (1) 1 , R 2 , R 3 As such, in order to more reliably modify cellulose, an alkoxy group having 1 to 3 carbon atoms or an alkyl group having 1 to 3 carbon atoms is more preferable, and an alkoxy group having 1 to 2 carbon atoms or an alkyl group having 1 to 2 carbon atoms is particularly preferable. Furthermore, in order to more reliably modify cellulose and reliably impart excellent hydrophobicity while more reliably suppressing aggregation of modified cellulose nanofibers, the R in the compound of general formula (1) is preferred. 1 , R 2 , R 3 Preferably, at least one of these is an alkoxy group having 1 to 5 carbon atoms, and at least one is an alkyl group having 1 to 5 carbon atoms.
[0027] In the compound of general formula (1), X is not particularly limited as long as it is an organic functional group containing an epoxy group, but in order to reliably impart excellent hydrophobicity, X is as shown in general formula (2) below. ER 4 -OR 5 - (2) (In general formula (2), E is an epoxy group, R 4 , R 5 Each of these independently represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms, preferably an aliphatic hydrocarbon group having 1 to 3 carbon atoms. Organic functional groups represented by ) are preferred.
[0028] Examples of silane coupling agents include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyl(dimethoxy)methylsilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. Of these, 3-glycidoxypropyl(dimethoxy)methylsilane is preferred because it reliably imparts superior hydrophobicity while more reliably suppressing aggregation of modified cellulose nanofibers.
[0029] <Modified cellulose nanofibers> The amount of silane coupling agent added to modified cellulose nanofibers is not particularly limited, but the lower limit is preferably 0.001 moles of silane coupling agent per 1.0 mole of cellulose β-glucose units, more preferably 0.005 moles, even more preferably 0.020 moles, and particularly preferably 0.20 moles, from the standpoint of reliably imparting excellent hydrophobicity to the cellulose. On the other hand, the upper limit of the amount of silane coupling agent added to modified cellulose nanofibers is preferably 3.0 moles per 1.0 mole of cellulose β-glucose units, from the standpoint of preventing loss of high strength by maintaining the crystalline structure of the cellulose nanofibers, and particularly preferably 1.0 mole per 1.0 mole of cellulose β-glucose units, from the standpoint of more reliably maintaining the crystalline structure of the cellulose nanofibers. The above-mentioned ratio of silane coupling agent to be added represents the ratio of silane coupling agent units to one β-glucose molecule, which is a constituent unit of cellulose.
[0030] The hydrophobicity (i.e., affinity for hydrophobic substances) of modified cellulose nanofibers can be evaluated by visually observing the dispersion state of the modified cellulose nanofibers in the organic solvent immediately after dispersing them in the organic solvent, or by visually observing the time required for the modified cellulose nanofibers to aggregate and settle in the organic solvent after dispersion. If the time required for the modified cellulose nanofibers to aggregate and settle in the organic solvent is greater than or equal to a predetermined time, it is proven that the modified cellulose nanofibers have excellent dispersibility in organic solvents and are hydrophobic.
[0031] Examples of organic solvents used to evaluate the dispersibility of modified cellulose nanofibers include tetrahydrofuran, acetone, ethanol, propanol, and other C1-C5 alcohols.
[0032] Furthermore, it can be confirmed by Fourier transform infrared spectroscopy (FT-IR) that at least a portion of the hydroxyl groups of cellulose are modified by a silane coupling agent containing epoxy groups. Specifically, by comparing the infrared absorption spectrum of untreated cellulose nanofibers (not modified by a silane coupling agent) with that of modified cellulose nanofibers, it can be confirmed that at least a portion of the hydroxyl groups of cellulose are modified by a silane coupling agent containing epoxy groups.
[0033] Specifically, in the modified cellulose nanofiber of the present invention, if the silane coupling agent has an alkyl group, the infrared absorption spectrum at 1260 cm² -1 , 798cm -1 , 763cm -1 In the region where absorption peaks originating from Si-C bonds appear, in untreated cellulose nanofibers, 1260 cm² is observed. -1 , 798cm -1 , 763cm -1No absorption peak appears in this region. Therefore, the infrared absorption spectrum at 1260 cm⁻¹ -1 , 798cm -1 , 763cm -1 By checking for the presence or absence of an absorption peak in this region, it is possible to determine whether or not the cellulose has been modified by a silane coupling agent.
[0034] Furthermore, in the modified cellulose nanofibers of the present invention, even when the silane coupling agent does not have an alkyl group, the infrared absorption spectrum at 900 cm² is -1 Absorption peaks originating from epoxy groups appear in the surrounding region. Even in untreated cellulose nanofibers, the infrared absorption spectrum shows 900 cm². -1 An absorption peak appears in the surrounding region, but in modified cellulose nanofibers, at 900 cm². -1 In the surrounding region, the absorption peaks originating from epoxy groups and cellulose nanofibers overlap, resulting in increased peak intensity. Therefore, 900 cm² -1 By checking the peak intensity in the surrounding region, it is possible to determine whether or not the cellulose has been modified with a silane coupling agent.
[0035] The size of the modified cellulose nanofibers of the present invention is not particularly limited, but corresponding to the fact that the average fiber diameter of the cellulose forming the backbone is less than 1.0 μm, for example, an average fiber diameter of less than 1.0 μm is possible. From the viewpoint of homogenizing the cellulose modification sites by the silane coupling agent and expanding the range of application of the modified cellulose nanofibers, the average fiber diameter is preferably 4 nm to 100 nm, and particularly preferably 10 nm to 50 nm. Furthermore, from the viewpoint of homogenizing the cellulose modification sites by the silane coupling agent and expanding the range of application of the modified cellulose nanofibers, the average fiber length is preferably 20 μm to 200 μm, and particularly preferably 50 μm to 150 μm.
[0036] The modified cellulose nanofibers of the present invention possess excellent hydrophobicity and have superior affinity for hydrophobic substances, resulting in excellent mixing and dispersibility with hydrophobic substances such as resins. Furthermore, even though the modified cellulose nanofibers of the present invention are modified, the molecular structure of the cellulose nanofibers themselves is suppressed, thus maintaining the original properties of the cellulose nanofibers. Therefore, because the modified cellulose nanofibers of the present invention have high strength, they exhibit excellent functionality as, for example, a reinforcing material for hydrophobic substances.
[0037] <Method for manufacturing modified cellulose nanofibers> The modified cellulose nanofibers of the present invention can be manufactured, for example, by a cellulose preparation step of preparing a cellulose aqueous dispersion in which cellulose (cellulose nanofibers) forming the backbone of the modified cellulose nanofibers is dispersed in water; a reaction solution preparation step of mixing a silane coupling agent having epoxy groups with the prepared cellulose aqueous dispersion to obtain a reaction solution; and a drying step of drying the obtained reaction solution to obtain modified cellulose nanofibers in which the hydroxyl groups of cellulose are modified with the silane coupling agent having epoxy groups.
[0038] As a cellulose preparation process, for example, one method is to defibrate a cellulose precursor derived from a natural product, which is used as a raw material, to convert the cellulose precursor into nanofibers and obtain cellulose nanofibers. The method for defibrating the cellulose precursor is not particularly limited and can include defibration using a mixer, high-speed homomixer, ultrasonic homogenizer, low-pressure homogenizer, high-pressure homogenizer, high-speed rotary mixer, grinder, freeze grinding, media mill, ball mill, etc.
[0039] One possible step in preparing the reaction solution is to add a predetermined amount of a silane coupling agent having epoxy groups to a cellulose aqueous dispersion in which cellulose nanofibers are dispersed in water. Another possible drying step is to remove water from the prepared reaction solution by drying it. [Examples]
[0040] Next, embodiments of the present invention will be described, but the present invention is not limited to these examples unless it exceeds the spirit of the invention.
[0041] <Fabrication of Modified Cellulose Nanofibers> Example 1 A reaction solution containing cellulose nanofibers and the silane coupling agent was prepared by dispersing 0.2 g of a cellulose nanofiber aqueous dispersion (average fiber length 100 μm, average fiber diameter 30-40 nm, "CellFim C-100 (approximately 95% by mass)" manufactured by Mori Machinery Co., Ltd.) in 95 g of water. A predetermined amount of 3-glycidoxypropyl (dimethoxy)methylsilane (hereinafter sometimes referred to as "GOPDMS," which corresponds to a silane coupling agent having an epoxy group) was added according to the following charging ratio, and the mixture was stirred for a predetermined time. The resulting reaction solution was dried to produce the modified cellulose nanofibers of Example 1, in which cellulose nanofibers were modified with GOPDMS. In Example 1, based on the mixing ratio of cellulose nanofibers and GOPDMS, the charging ratio of GOPDMS per 1.0 mole of β-glucose units of cellulose was 3.0 moles.
[0042] The modification of cellulose nanofibers with GOPDMS was confirmed by analyzing the compound obtained in Example 1 using FT-IR (Spectrum One(A) from PerkinElmer Corporation), and the obtained infrared absorption spectrum was found at 1260 cm⁻¹. -1 , 798cm -1 , 763cm -1 Absorption peaks originating from Si-C bonds appear in this region, and compared to cellulose nanofibers before modification with GOPDMS, the infrared absorption spectrum at 900 cm² is different. -1 This was confirmed by the strong peak intensity in the surrounding area.
[0043] Example 2 Modified cellulose nanofibers for Example 2 were prepared in the same manner as in Example 1, except that instead of using GOPDMS, a predetermined amount of 3-glycidoxypropyltrimethoxysilane (hereinafter sometimes referred to as "GOPTS," which corresponds to a silane coupling agent having an epoxy group) was used in the following charging ratio. In Example 2, based on the mixing ratio of cellulose nanofibers and GOPTS, the charging ratio of GOPTS per 1.0 mole of cellulose β-glucose units was 3.0 moles.
[0044] The modification of cellulose nanofibers with GOPTS was confirmed by analyzing the compound obtained in Example 2 using FT-IR, as in Example 1, and observing the 900 cm⁻¹ infrared absorption spectrum. -1 The peak intensity in the vicinity is the same as that of cellulose nanofibers before modification with GOPTS at 900 cm². -1 This was confirmed by its higher peak intensity compared to that in the surrounding area.
[0045] Comparative Example 1 The cellulose nanofibers used in Examples 1 and 2 were those not modified with a silane coupling agent.
[0046] <Evaluation Criteria> (1) Dispersibility (hydrophobicity) 0.02 g each of the modified cellulose nanofiber samples from Examples 1 and 2, and the unmodified cellulose nanofiber sample from Comparative Example 1, was weighed out and added to 20 ml of tetrahydrofuran in a container. The mixture was stirred with a stirrer at a stirring speed of 1350 rpm for 24 hours to prepare the first dispersion. Furthermore, 1.0 ml of the prepared first dispersion was taken and placed in another container, and 10 ml of tetrahydrofuran was added to prepare the second dispersion, which was used as the dispersion sample.
[0047] The dispersion state of the cellulose nanofiber sample in tetrahydrofuran immediately after the preparation of the second dispersion (5 seconds after preparation) was visually observed and evaluated as follows. ◎: The dispersion state of the cellulose nanofiber sample is excellent, and the cellulose nanofiber sample exhibits excellent hydrophobicity. ○: Although some aggregation of the cellulose nanofiber sample is observed, the dispersion is good, and hydrophobicity is observed in the cellulose nanofiber sample. ×: Most of the cellulose nanofiber samples were in an aggregated state, and hydrophobicity was not observed in the cellulose nanofiber samples.
[0048] (2) Settlement time For the dispersion samples prepared as described above, the time from immediately after the preparation of the second dispersion until the amount of cellulose nanofiber sample settled was measured as the settling time. The settling time was tested for n=3 for each of Examples 1 and 2 and Comparative Example 1, and the average value was evaluated as follows. ◎: Sinking time 100 seconds or more ○: Sinking time 40 seconds or more but less than 100 seconds ×: Sinking time less than 40 seconds
[0049] The evaluation results are shown in Table 1 below. Regarding the evaluation of dispersibility, Figure 1(a) shows a photograph of the dispersion state immediately after preparation of the dispersion sample using tetrahydrofuran as the dispersion solvent in Example 1, Figure 1(b) shows a photograph of the dispersion state immediately after preparation of the dispersion sample using tetrahydrofuran as the dispersion solvent in Example 2, and Figure 1(c) shows a photograph of the dispersion state immediately after preparation of the dispersion sample using tetrahydrofuran as the dispersion solvent in Comparative Example 1.
[0050] [Table 1]
[0051] As shown in Table 1 above, in Examples 1 and 2, which are modified cellulose nanofibers modified with a silane coupling agent having epoxy groups, the dispersibility was rated ○ or higher, and the sedimentation time was also rated ○ or higher, demonstrating excellent dispersion properties with respect to hydrophobic organic solvents. In particular, Example 1, which used 3-glycidoxypropyl(dimethoxy)methylsilane, showed even better dispersibility and sedimentation time compared to Example 2, which used 3-glycidoxypropyltrimethoxysilane. This is thought to be partly due to the difference in the number of silanol groups generated by the hydrolysis of the hydrolyzable silyl groups of the silane coupling agent.
[0052] On the other hand, in Comparative Example 1, which was an unmodified cellulose nanofiber not modified with a silane coupling agent containing epoxy groups, dispersibility with hydrophobic substances was not obtained, the sedimentation time was short, and dispersion characteristics were not achieved. [Industrial applicability]
[0053] The modified cellulose nanofibers of the present invention maintain the molecular structure of the cellulose nanofibers while being endowed with excellent hydrophobicity and exhibiting superior affinity with hydrophobic substances. Therefore, they can be used in a wide range of fields, and are particularly valuable in the field of resin compositions used as materials for molded products.
Claims
1. At least a portion of the hydroxyl groups of cellulose are modified by a silane coupling agent represented by the following general formula (1), A modified cellulose nanofiber in which the hydroxyl groups of the cellulose are chemically bonded to silanol groups generated by the hydrolysis of the hydrolyzable silyl groups of the silane coupling agent. 【Chemistry 1】 (In general formula (1), X represents an organic functional group containing an epoxy group, and R １ , R ２ , R ３ Of these, two are alkoxy groups with 1 to 5 carbon atoms, and one is an alkyl group with 1 to 5 carbon atoms.
2. The modified cellulose nanofiber according to claim 1, wherein the silane coupling agent comprises 3-glycidoxypropyl (dimethoxy)methylsilane.
3. The modified cellulose nanofiber according to claim 1 or 2, wherein the average fiber length is 20 μm or more and 200 μm or less, and the average fiber diameter is 4 nm or more and 100 nm or less.