JP6680629B2 - Modified cellulose fiber and method for producing the same - Google Patents

Description

  The present invention relates to a modified cellulose fiber modified with a compound having a 9,9-bisarylfluorene skeleton and useful as a resin composite material, a method for producing the modified cellulose fiber, and a resin composition containing the modified cellulose fiber.

  Cellulose, which is a fiber of plant origin, has a small environmental load, is a sustainable resource, and has excellent properties such as high elastic modulus, high strength, and low linear expansion coefficient. Therefore, they are used in a wide range of applications, for example, as materials for paper, films and sheets, and resin composite materials (for example, resin reinforcing agents). In particular, micronized cellulose fibers (such as nanofibers) are useful as a reinforcing agent for resins, and attempts have been made to produce cellulose nanofibers from cellulose raw materials (such as wood and pulp).

  As a method for producing cellulose nanofibers (for example, nanofibers), mechanical defibration methods such as a method for beating cellulose (for example, pulp) and a method for homogenizing are generally used. However, these defibration methods may damage the cellulose nanofibers, leading to a decrease in elastic modulus and low linear expansion characteristics.

  On the other hand, a method for producing cellulose fibers that does not require a mechanical defibration method is also disclosed. For example, Japanese Patent Application Laid-Open No. 2011-225847 (Patent Document 1) discloses that a compound containing a cellulose-containing component (a cellulose-containing component containing an amorphous component such as lignin or hemicellulose) and a 9,9-bisarylfluorene skeleton (simply fluorene). Compound)) and selectively solubilize or extract amorphous components such as lignin and hemicellulose to produce crystalline cellulose (or cellulose fiber) with less damage. In the examples of this document, Yonematsu and 9,9-bis [4- (2-hydroxyethoxy) phenyl] fluorene (BPEF) were heated and mixed at high temperature in an autoclave to obtain a solvent (mixture of dioxane and water). After removing the BPEF in step 1, the filter residue is redispersed in water and dispersed by a paint shaker to obtain a cellulose fiber in the form of an aqueous dispersion.

  However, even if the amorphous component is solubilized or extracted and removed and the dried cellulose fiber is added to the resin as it is, the cellulose fiber is agglomerated and cannot be dispersed uniformly. Therefore, it is necessary to disperse the cellulose fiber obtained by solubilizing or extracting the amorphous component with a disperser such as a paint shaker. Furthermore, since the fluorene compound is not bound to the cellulose nanofibers, if it is used for forming a composite with a matrix resin, the fluorene compound may be transferred to the matrix component and the properties of the composite may be deteriorated.

  In JP-A-2016-79370 (Patent Document 2), cellulose nanofibers are reacted with a fluorene compound having a carboxyl group and / or an epoxy group in an organic solvent, and the fluorene compound is 0.01 to 25% by weight. It is described that the modified cellulose bonded to the cellulose in the ratio of (modified powder in the form of powder) is obtained. In the examples of this document, the water in the cellulose nanofiber aqueous dispersion was solvent-substituted with dimethylacetamide and reacted with a fluorene compound having an epoxy group, and the modification ratio was 8.9% by weight or 16% by weight. Is being prepared.

  However, in the method of Reference 2, since the reaction between the hydroxyl group of cellulose and the epoxy group of the fluorene compound is used, the reaction site is specified, and it may be impossible to modify the cellulose nanofiber with the fluorene compound while activating it. The dispersion stability of the modified cellulose nanofiber is still insufficient.

  Japanese Unexamined Patent Publication No. 2009-67817 (Patent Document 3) describes that a polymerization initiator is used to graft-modify a polymerizable compound onto a cellulose fiber in an aqueous system, and the grafting rate may be 5 to 1000%. Has been described. JP-A-2013-234283 (Patent Document 4) discloses that in a water dispersion of cellulose fibers, a polymerizable monomer is graft-polymerized onto the cellulose fibers in the presence of a water-soluble radical generator and a dispersant, It is described that a graft polymer-modified cellulose fiber is produced by purification. This document also describes that the mass ratio of the polymerizable monomer to the cellulose fiber is 99.9 / 0.1 to 50/50, and in the examples, the grafting ratio of the polymer to the cellulose fiber is It is also described that 54 to 134% by weight of modified cellulose fibers were obtained.

  However, in the methods of Documents 3 and 4, since the dispersion medium of the modified cellulose fiber is an aqueous solvent, complicated methods such as a method of impregnating or mixing with a liquid matrix material and a method of melt-kneading with a resin after removing water are complicated. It is necessary to form a composite with a resin by any method, and it is difficult to form a composite directly. Moreover, since a homopolymer of a polymerizable monomer is produced, it is difficult to industrially advantageously manufacture the modified cellulose fiber. Furthermore, in the example of Document 3, the higher the grafting rate of methyl methacrylate or styrene, the higher the tendency of the fiber-reinforced composite material to develop physical properties, and therefore the modification rate (grafting rate) of 10% or less. It is considered that the above-mentioned cellulose fiber does not exhibit a sufficient effect. In the method of Reference 4, not only it is necessary to modify with a large amount of the graft polymer, but also the content of cellulose fiber in the modified cellulose fiber is low. Therefore, the content of cellulose fiber should be increased in the composite with the resin. Is difficult. Furthermore, since the content of the grafted polymer is large, the types of compatible or dispersible resins and the types of solvents are restricted.

JP, 2011-225847, A (claim, [0027] "0072" [0090] [0098], an example). JP-A-2016-79370 (Claims, Examples) JP, 2009-67817, A (claim, [0044], an example) JP, 2013-234283, A (claim, [0015] [0016], an example)

  Therefore, an object of the present invention is to provide a modified cellulose fiber which has a high dispersibility in an organic medium (resin etc.) even if the modification ratio is small, and is useful for compounding with a resin, a method for producing the modified cellulose fiber, and a resin containing the modified cellulose fiber. To provide a composition.

  Another object of the present invention is to produce a modified cellulose fiber which does not form a homopolymer of a polymerizable monomer and which can be effectively complexed with a resin by adding a small amount thereof, a method for producing the modified cellulose fiber, and the modified cellulose fiber. It is to provide a resin composition containing the same.

  Still another object of the present invention is to provide a modified cellulose fiber having high crystallinity and capable of effectively reinforcing a resin, a method for producing the modified cellulose fiber, and a resin composition containing the modified cellulose fiber.

  The inventors of the present invention have made extensive studies to achieve the above-mentioned object, and as a result, activated cellulose fibers in the presence of a radical activator to obtain a fluorene compound having a phenolic hydroxyl group (9,9-bishydroxyarylfluorene skeleton). Compound having a), because the active radicals of the cellulose fiber pull out the hydrogen atom of the phenolic hydroxyl group and couple it, it is possible to obtain a modified cellulose nanofiber in which the fluorene compound is bonded to the cellulose nanofiber, The modified cellulose nanofibers have high affinity and dispersibility for an organic medium (resin etc.) even if the binding ratio (modification amount) of the fluorene compound is small, and found that they can be effectively combined with a resin. Was completed.

  That is, the modified cellulose fiber of the present invention is a compound having a 9,9-bisarylfluorene skeleton represented by the following formula (1) and a cellulose fiber activated by a radical in a solvent (hereinafter, simply referred to as phenolic fluorene). (Sometimes referred to as a compound). In other words, it is possible to obtain a modified cellulose fiber by heat-treating (or activating) the cellulose fiber in the presence of a radical generator and reacting the activated cellulose fiber with the fluorene compound for coupling. it can.

(In the formula, ring Z is an arene ring; n is an integer of 1 or more; R ¹ and R ² are substituents; p is 0 or an integer of 1 or more; k is an integer of 0 to 4)

  In the formula (1), the ring Z may be a monocyclic arene ring, a polycyclic arene ring or a ring-collecting arene ring (for example, a benzene ring, a naphthalene ring or a biphenyl ring), and n is 1 independently. It may be an integer of 3 (eg, 1 or 2).

R ¹ is an alkyl group (for example, a C _1-4 alkyl group) or an alkoxy group, p is an integer of 0 to 3 (for example, an integer of 0 to 2), and R ² is a cyano group, a halogen atom or an alkyl group (for example, C _1-4 alkyl group), k may be an integer of 0 to 3 (for example, 0 or 1).

  The ratio of the compound represented by the formula (1) bonded to the cellulose fiber may be about 0.01 to 20% by weight based on the total amount of the modified cellulose fiber. The modified cellulose fiber may be a nanofiber, for example, a nanofiber having an average fiber diameter of about 5 to 500 nm. Furthermore, the crystallinity of the modified cellulose fiber may be 60% or more (for example, about 75 to 90%). The modified cellulose fiber can also be used as a reinforcing material for resin.

  The present invention also includes a resin composition containing the modified cellulose fiber.

  In the present invention, a cellulose fiber is heat-treated (or activated) in a solvent (for example, an organic solvent) in the presence of a radical generator to react with the compound represented by the formula (1) (or under heat). The method for producing the modified cellulose fiber is also included. Cellulose fibers (eg, nanocellulose fibers) may be derived, for example, from at least one pulp selected from wood pulp and cotton linter pulp, and crystalline cellulose fibers (eg, cellulose fibers having a type I crystal structure). ) May be sufficient.

  Since the fluorene compound is graft-bonded to the cellulose fiber of the modified cellulose fiber of the present invention, it has a high affinity or miscibility with various organic media (resins etc.) even with a small modification rate. It has a high dispersibility with respect to the resin and a high reinforcing property. Therefore, it is useful for compounding with a resin. In addition, a homopolymer of a polymerizable monomer is not formed, and even if added in a small amount, it can be effectively compounded with a resin, and the characteristics of the resin are not impaired. Furthermore, since the decomposition of the cellulose fiber can be suppressed and the crystallinity can be maintained, a modified cellulose fiber having a high molecular weight and high crystallinity can be obtained. Such a modified cellulose fiber has excellent properties such as high strength, high elastic modulus, and low linear expansion property, and can be easily dispersed in a resin, so that it is useful as a resin composite material (for example, a reinforcing material). is there.

FIG. 1 is a photograph showing the dispersibility of the modified cellulose nanofibers obtained in Example 1 and Comparative Example 1.

  The modified cellulose fiber of the present invention includes a cellulose fiber and a compound having a 9,9-bisarylfluorene skeleton bonded to the cellulose fiber.

[Cellulose fiber]
As cellulose, lignin, pulp with a low content of non-cellulosic components such as hemicellulose, for example, plant-derived cellulose raw material {for example, wood [for example, conifers (pine, fir, spruce, hemlock, cedar, etc.), hardwood (beech) , Hippo, poplar, maple, etc.), herbs (linen (hemp, flax, manila hemp, ramie, etc.), straw, bagasse, mitsumata, etc.), seed hair fiber (cotton linter, bombax cotton, kapok, etc.), Pulp and the like produced from bamboo, sugar cane, etc., animal-derived cellulose raw materials (such as ascidian cellulose), and bacterial-derived cellulose raw materials (such as cellulose contained in nata de coco). These celluloses can be used alone or in combination of two or more kinds. Among these celluloses, wood pulp (for example, softwood pulp, hardwood pulp, etc.), seed hair fiber-derived pulp (for example, cotton linter pulp), and the like are preferable. The pulp may be mechanical pulp obtained by mechanically treating the pulp material, but chemical pulp obtained by chemically treating the pulp material is preferable because the content of the non-cellulose component is small. In addition, the cellulose is preferably cellulose fibers obtained by micronizing (microfibrillating) the above-exemplified pulp (for example, chemical pulp), particularly cellulose nanofibers.

  The ratio (content) of cellulose to the total amount of cellulose fibers and non-cellulose components is, for example, 70% by weight or more (for example, 75 to 100% by weight), preferably 80% by weight or more (for example, 85 to 100% by weight). More preferably, it may be about 90% by weight or more (for example, 95 to 100% by weight).

  The average fiber diameter of the cellulose fibers may be a micrometer size (for example, 1 to 20 μm), but from the viewpoint of the reinforcing property of the resin, a nanometer size, for example, 2 to 1000 nm (for example, 4 to 700 nm), The thickness may be preferably 5 to 500 nm (eg, 7 to 250 nm), more preferably 10 to 100 nm, or 10 to 80 nm (eg, 20 to 70 nm, particularly 25 to 50 nm).

  The average fiber length of the cellulose fibers can be selected, for example, from the range of about 0.01 to 500 μm (eg, 0.05 to 400 μm), and is usually 0.1 to 300 μm (eg, 0.1 to 200 μm), preferably It may be about 0.2 to 100 μm (for example, 0.3 to 80 μm), and more preferably about 0.5 to 30 μm (for example, 0.5 to 10 μm).

  Furthermore, the ratio (aspect ratio) of the average fiber length to the average fiber diameter of the cellulose fibers is, for example, 5 or more (eg, about 5 to 10000), preferably 10 or more (eg, about 10 to 5000), and more preferably 20. Above (for example, about 20 to 3000), particularly 50 or more (for example, about 50 to 2000), 100 or more (for example, 100 to 1000), and further 200 or more (for example, 200 to 800) May be If the aspect ratio is too small, the reinforcing effect of the resin is lowered, and if the aspect ratio is too large, the fibers may be easily decomposed (or damaged).

  The cellulose fiber may be a highly crystalline cellulose fiber, and the crystallinity of the cellulose fiber is, for example, 40 to 100% (for example, 50 to 100%), preferably 60 to 95%, and more preferably 70. ˜90% (for example, 75 to 90%), and usually the crystallinity may be 60% or more. In the production method of the present invention, the crystallinity of the cellulose fiber can be maintained, so that the use of cellulose having a high crystallinity makes it possible to obtain a highly crystalline modified cellulose fiber. Therefore, crystalline cellulose may be preferably used. As the crystal structure of the cellulose fiber, for example, I-type, II-type, III-type, IV-type and the like can be exemplified, and the I-type crystal structure having low linear expansion characteristics and elastic modulus is preferable.

(Phenolic fluorene compound)
The phenolic fluorene compound has a 9,9-bisaryl skeleton and is represented by the following formula (1).

(In the formula, ring Z is an arene ring; n is an integer of 1 or more; R ¹ and R ² are substituents; p is 0 or an integer of 1 or more; k is an integer of 0 to 4)

  In the above formula (1), examples of the arene ring represented by the ring Z include a monocyclic arene ring such as a benzene ring and a polycyclic arene ring. The polycyclic arene ring includes a condensed polycyclic arene. A ring (fused polycyclic hydrocarbon ring), a ring-collecting arene ring (ring-collecting aromatic hydrocarbon ring) and the like are included.

Examples of the fused polycyclic arene ring include a fused bicyclic arene (eg, fused bicyclic C _10-16 arene such as naphthalene) ring, a fused tricyclic arene (eg, anthracene, phenanthrene, etc.) ring, and the like. Examples include fused bi- to tetra-cyclic arene rings. Examples of preferable fused polycyclic arene ring include naphthalene ring and anthracene ring, and naphthalene ring is particularly preferable. The two rings Z may be the same or different rings.

Examples of the ring-collecting arene ring include a bilane ring, for example, a biphenyl ring, a binaphthyl ring, a biC _6-12 arene ring such as a phenylnaphthalene ring (1-phenylnaphthalene ring, 2-phenylnaphthalene ring, etc.), a terarene ring, for example, An example is a ter C _6-12 arene ring such as a terphenylene ring. Preferred ring-assembled arene rings include biC _6-10 arene rings, especially biphenyl rings.

  The number of substitutions n of the hydroxyl group with respect to the ring Z is independently an integer of 1 or more (for example, an integer of 1 to 4), preferably an integer of 1 to 3, more preferably an integer of 1 or 2, and particularly 1. May be. The number of substitutions n may be the same or different in each ring Z.

  The hydroxyl group (phenolic hydroxyl group) can be substituted at an appropriate position on the ring Z. For example, when the ring Z is a benzene ring, the 2-, 3-, 4-positions of the phenyl group (particularly, 3-position and / or 4-position) in many cases, and when ring Z is a naphthalene ring, it is often in the 5-8-position of the naphthyl group, for example, 9- of fluorene. 1-position or 2-position of the naphthalene ring is substituted with respect to the position (substitution in the relation of 1-naphthyl or 2-naphthyl), and 1,5-position, 2,6-position with respect to this substitution position. In many cases, the hydroxyl group is substituted in such a relationship (especially when n is 1, the relationship at the 2,6-position). Further, when n is 2 or more, the substitution position is not particularly limited. Further, in the ring-assembled arene ring Z, the substitution position of the hydroxyl group is not particularly limited, and, for example, even if it is substituted with the arene ring bonded to the 9-position of fluorene and / or the arene ring adjacent to this arene ring. Good. For example, the 3-position or 4-position of the biphenyl ring Z may be bonded to the 9-position of fluorene, and when the 4-position of the biphenyl ring Z is bonded to the 9-position of fluorene, The substitution position may be any of 2-, 3-, 2'-, 3'-, 4'-positions, usually 2-, 3'-, 4'-positions, preferably 2-, 4 It may be substituted at the'-position (particularly at the 2-position).

In the above formula (1), the substituent R ¹ is a halogen atom (eg, fluorine atom, chlorine atom, bromine atom, iodine atom), alkyl group (methyl group, ethyl group, propyl group, isopropyl group, butyl group, Linear or branched C _1-10 alkyl group such as s-butyl group and t-butyl group, preferably linear or branched C _1-6 alkyl group, more preferably linear or branched chain etc. Jo _{C 1-4} alkyl group), a cycloalkyl group (cyclopentyl group and _{C 5-10} cycloalkyl groups such as cyclohexyl group), an aryl group [phenyl group, alkylphenyl group (methylphenyl (tolyl) group, Dimethylphenyl (xylyl) group, etc., biphenyl group, C _6-12 aryl group such as naphthyl group], aralkyl group (C such as benzyl group, phenethyl group etc.) _6-10 aryl-C _1-4 alkyl group), an alkoxy group (for example, a methoxy group, an ethoxy group, a propoxy group, an n-butoxy group, an isobutoxy group, a t-butoxy group, or another linear or branched C). _1-10 alkoxy group), cycloalkoxy group (for example, C _5-10 cycloalkyloxy group such as cyclohexyloxy group), aryloxy group (for example, C _6-10 aryloxy group such as phenoxy group) , Aralkyloxy groups (eg, C _6-10 aryl-C _1-4 alkyloxy groups such as benzyloxy group), alkylthio groups (eg, methylthio group, ethylthio group, propylthio group, n-butylthio group, t-butylthio group) Groups such as C _1-10 alkylthio groups), cycloalkylthio groups (eg cyclohexyl) A C _5-10 cycloalkylthio group such as a ruthio group), an arylthio group (eg, a C _6-10 arylthio group such as a thiophenoxy group), an aralkylthio group (eg a C _6-10 aryl-C such as a benzylthio group). _1-4 alkylthio group), acyl group (for example, C _1-6 acyl group such as acetyl group), carboxy group, alkoxycarbonyl group (for example, C _1-4 alkoxy-carbonyl group such as methoxycarbonyl group) , Nitro group, cyano group, dialkylamino group (eg, diC _1-4 alkylamino group such as dimethylamino group), dialkylcarbonylamino group (eg, diC _1-4 alkyl-carbonylamino group such as diacetylamino group) Groups, etc.) and the like.

Of these substituents R ¹ , typically, a halogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, an alkoxy group, an acyl group, a carboxy group, a nitro group, a cyano group, a substituted amino group and the like. Can be mentioned. Preferable substituent R ¹ includes a linear or branched C _1-4 alkyl group such as an alkoxy group and an alkyl group, particularly a methyl group. When the substituent R ¹ is an aryl group, the substituent R ¹ together with the ring Z may form the ring-collecting arene ring. The types of the substituents R ¹ may be the same or different in the same or different ring Z.

The number of substitutions p can be appropriately selected depending on the type of the ring Z, and may be, for example, an integer of 0 to 8, an integer of 0 to 4, preferably 0 to 3 (for example, 0 to 2). ), Especially 0 or 1. Particularly when p is 1, the ring Z may be a benzene ring, a naphthalene ring or a biphenyl ring, and the substituent R ¹ may be a methyl group.

As the substituent R ² , a cyano group, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), a carboxy group, an alkoxycarbonyl group (for example, a C _1-4 alkoxy-carbonyl group such as a methoxycarbonyl group), an alkyl group (C _1-6 alkyl group such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, t-butyl group) and aryl group (C _6-10 aryl group such as phenyl group).

Of these substituents R ² , typically, an alkyl group, a carboxy group, a C _1-2 alkoxy-carbonyl group, a cyano group, a halogen atom, or the like, particularly a linear or branched C ₁ group such as a methyl group or the like. _-4 Alkyl groups are preferred. The substitution number k is an integer of 0 to 4 (for example, 0 to 3), preferably an integer of 0 to 2 (for example, 0 or 1), and particularly 0. The substitution numbers k may be the same or different from each other, and when k is 2 or more, the types of the substituents R ² may be the same or different from each other, and the two benzene rings of the fluorene ring are substituted. The types of the substituents R ² may be the same or different. The substitution position of the substituent R ² is not particularly limited and may be, for example, the 2-position to the 7-position (2-position, 3-position and / or 7-position) of the fluorene ring.

In the formula (1), as the compound in which n is 1, 9,9-bis (hydroxyaryl) fluorenes (for example, 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (3 -Hydroxyphenyl) fluorene, 9,9-bis (6-hydroxy-2-naphthyl) fluorene, 9,9-bis (5-hydroxy-1-naphthyl) fluorene and other 9,9-bis (hydroxy C _6-12) Aryl) fluorene, 9,9-bis (3-phenyl-4-hydroxyphenyl) fluorene, 9,9-bis (4-phenyl-3-hydroxyphenyl) fluorene and other 9,9-bis (C _6-12 aryl) - hydroxy _{C 6-12} aryl) fluorene, 9,9-bis (3-methyl-4-hydroxyphenyl) fluorene, 9,9-bis (4 Methyl-3-hydroxyphenyl) fluorene such as 9,9-bis _{(C 1-4} alkyl - hydroxy _{C 6-12} aryl) fluorene, and others.

In the formula (1), as the compound in which n is 2 or more, 9,9-bis [(poly) hydroxyaryl] fluorenes {9,9-bis (3,4-dihydroxyphenyl) fluorene, 9,9 Examples include 9,9-bis (di or trihydroxy C _6-12 aryl) fluorene and the like} such as -bis (2,4-dihydroxyphenyl) fluorene and the like.

  As the compound having a 9,9-bisarylfluorene skeleton represented by the formula (1) (phenolic fluorene compound), a commercially available product may be used, and a conventional method (for example, 9-fluorenones and It may be synthesized by a reaction with a hydroxy group-containing arene ring compound (eg, phenols, naphthols, etc.) in the presence of an acid catalyst.

  Since the fluorene compound is compatible with various resins, it is useful as a hydrophobizing modifier for cellulose fibers [eg, cellulose nanofibers (CNF)].

(Modified cellulose fiber)
In the modified cellulose fiber (or modified cellulose fiber, cellulose fiber derivative), the phenolic fluorene compound represented by the above formula (1) is bonded to the cellulose fiber. In addition to this, in addition to the abstraction reaction in which the hydrogen atoms of the cellulose fiber are randomly abstracted by the radical (or the reaction of forming a radical in the cellulose fiber), a random phenolic fluorene compound represented by the formula (1) is added to this bond. Since the reaction is involved, it is difficult to identify the binding site of the phenolic fluorene compound represented by the formula (1) to the cellulose fiber and the structure of the modified cellulose fiber even with the current analytical technique. Therefore, the modified cellulose fiber may be a product obtained by the method described below (reaction of a cellulose fiber treated with a radical generator with a fluorene compound represented by the formula (1)).

  The modified cellulose fiber shows a high affinity for the organic medium even if the ratio of the fluorene compound bonded (or modified) to the cellulose fiber is relatively small. The ratio of the fluorene compound bonded to the cellulose fibers (hereinafter referred to as the modification ratio) can be selected from the range of about 0.01 to 20% by weight based on the total amount of the modified cellulose fibers, and for example, 0.05 to 15% by weight. %, Preferably 0.1 to 10% by weight (eg 0.3 to 7% by weight), more preferably 0.5 to 5% by weight (eg 0.7 to 3% by weight). . If the modification rate is too large, properties such as a low linear expansion coefficient may deteriorate, and if it is too small, dispersibility (or miscibility) in the resin may decrease.

  The ratio (content) of the modified cellulose fibers to the total amount of the modified cellulose fibers and the non-cellulose component may be the same as that of the cellulose fibers (for example, 90% by weight or more). If the content of the modified cellulose fiber is too small, the reinforcing property of the resin may decrease.

  The average particle diameter (average major diameter and average minor diameter) of the modified cellulose fibers can be selected from the range of, for example, 3 nm to 100 μm (for example, 3 nm to 30 μm), and is usually 5 nm to 10 μm (for example, 7 nm to 7 μm), preferably 10 nm to 5 μm (for example, 20 nm to 3 μm), and more preferably about 30 nm to 2 μm (for example, 50 nm to 1 μm). If the average particle size is too large, the dispersibility in the resin will decrease, and if it is too small, the handleability may decrease. The average particle diameter can be measured using a dry sieving method, a laser diffraction method, or the like.

  Since it is possible to suppress the decomposition of the cellulose fiber in the production process of the modified cellulose fiber, the average fiber diameter of the modified cellulose fiber, the value of the average fiber length and the aspect ratio correspond to each characteristic of the cellulose fiber, The numerical values of the average fiber diameter, the average fiber length and the aspect ratio can be referred to as they are. For example, the average fiber diameter of the modified cellulose fiber may be a micrometer size (for example, 1 to 10 μm), but a nanometer size modified cellulose fiber (cellulose nanofiber) is preferable. The average fiber diameter of the modified cellulose fiber may be in the same range as that of the cellulose fiber (for example, 5 to 500 nm). The modified cellulose fiber may have an average fiber length (for example, 0.1 to 200 μm) and an aspect ratio (for example, 20 to 3000) in the same range as the cellulose fiber. When the aspect ratio is within the predetermined range, the reinforcing effect of the resin can be improved.

  The modified cellulose fiber has a low water content, probably because the hydrophobicity is improved by the modification of the fluorene compound. That is, the saturated water absorption may be 8% by weight or less (for example, 5% by weight or less), and the water content is 0 to 7% by weight when left for one day under the conditions of a temperature of 25 ° C. and a humidity of 60%. % (For example, 0 to 5% by weight), preferably 5% by weight or less (for example, 0.1 to 5% by weight), and more preferably about 3% by weight or less. The water content can be measured using a near infrared analyzer or the like.

  Furthermore, in order to allow the resin to effectively exhibit the properties of the modified cellulose fiber (for example, low linear expansion property, strength, heat resistance, etc.), the modified cellulose fiber having high crystallinity is preferable. As described above, since the modified cellulose fiber of the present invention can maintain the crystallinity of the cellulose fiber, the crystallinity of the modified cellulose fiber can be directly referred to the numerical value of the cellulose fiber. For example, the crystallinity of the modified cellulose fiber is 40 to 95% (eg, 50 to 90%), preferably 60 to 95% (eg, 65 to 90%), more preferably 70 to 90% (eg, 75). ˜85%), and usually the crystallinity may be 60% or more (eg, about 75 to 90%). If the crystallinity is too low, properties such as low linear expansion properties and strength may be deteriorated. The crystallinity can be measured by the method described in Examples.

(Production method)
In the production method of the present invention, the cellulose fiber is subjected to heat treatment in a solvent (typically an organic solvent) in the presence of a radical generator to react with the compound represented by the formula (1), whereby the modification is carried out. Cellulose fibers can be prepared. That is, a predetermined modified cellulose fiber can be prepared by reacting a radical-activated cellulose fiber with a phenolic fluorene compound represented by the above formula (1) in a solvent. Although the reaction mechanism is not clear, by treating the cellulose fiber with a radical generator, the generated radical is trapped in the cellulose fiber or a radical is formed by a hydrogen abstraction reaction, and this radical is represented by the above formula (1). It is presumed that the hydrogen atom of the phenolic hydroxyl group of the fluorene compound represented (or a suitable place of the fluorene compound) is extracted to cause a coupling reaction, and the fluorene compound represented by the formula (1) is bonded to the cellulose fiber. To be done. Even if the radical generator, the cellulose fiber and the fluorene compound represented by the above formula (1) are added to the reaction system all at once and reacted, the modification reaction rarely occurs. The reason for this is not clear, but since the hydrogen atom abstraction reaction of the phenolic hydroxyl group is likely to occur, the radical is more likely to react with the phenolic hydroxyl group hydrogen atom abstraction reaction than the cellulose hydroxyl group hydrogen atom abstraction reaction. It is presumed that it will be preferentially consumed.

  The ratio of the cellulose fibers can be selected from the range of about 0.1 to 500 parts by weight (e.g., 1 to 300 parts by weight) with respect to 100 parts by weight of the phenolic fluorene compound, and for example, 5 to 200 parts by weight (e.g., 10 to 150 parts by weight), preferably about 5 to 100 parts by weight (for example, 10 to 50 parts by weight).

  As the radical generator, a conventional polymerization initiator, for example, an azo radical polymerization initiator (for example, 2,2′-azobis (isobutyronitrile), 2,2′-azobis [N- (2-hydroxyethyl) ) -2-Methylpropanamide] and the like, azonitrile compounds, azoamide compounds, azoamidine compounds and the like), organic or inorganic peroxides [dialkyl peroxides (for example, di-t-butyl peroxide and the like), diacyl peroxides ( For example, lauroyl peroxide, benzoyl peroxide, etc.), peracid (or perester) (eg, t-butyl hydroperoxide, cumene hydroperoxide, t-butyl peracetate, etc.) ketone peroxides, peroxycarbonates , Peroxyketals, etc.] and the like. These polymerization initiators can be used alone or in combination of two or more kinds.

  The preferred polymerization initiator (radical generator) may be a polymerization initiator having a long half-life.

  The amount of the radical generator used is, for example, 1 to 1000 parts by weight (eg, 5 to 800 parts by weight), preferably 10 to 750 parts by weight (eg, 50 to 700 parts by weight), relative to 100 parts by weight of the cellulose fiber. And more preferably about 100 to 600 parts by weight. Moreover, the usage-amount of a radical generator is 0.1-750 weight part (for example, 1-600 weight part) with respect to 100 weight part of phenolic fluorene compounds, Preferably it is 5-500 weight part (for example, 10-weight part). It may be about 400 parts by weight) or about 5 to 100 parts by weight (for example, 20 to 80 parts by weight).

  The reaction may be carried out in the absence of an organic solvent, but it is usually carried out in the presence of an organic solvent. The organic solvent may be impregnated in the cellulose fiber, but the reaction is often performed in a dispersion system in which the cellulose fiber is dispersed in the organic solvent. When the cellulose fibers (particularly nanofibers) and the phenolic fluorene compound are reacted with each other in a dispersion system in which the cellulose fibers are dispersed in an organic solvent, they can be reacted uniformly. The modified cellulose fiber obtained by such a method has high handleability and dispersibility in a resin, and is excellent in the reinforcing effect of the resin.

  When the cellulose fibers (particularly, microfibrillated fibers, nanofibers having an average fiber diameter of nanometer size) are dried, the fibers may become entangled and cannot be redispersed. Therefore, in general, cellulose fibers are often commercially available as a water-impregnated or water-dispersed liquid. In such an aqueous dispersion, a conventional solvent replacement method for substituting water in the aqueous dispersion with an organic solvent, for example, a water-soluble solvent is added to and mixed with an aqueous dispersion of cellulose fibers to separate the cellulose fibers (or the solvent. The dispersion liquid in which the cellulose fibers are dispersed in the organic solvent can be prepared by a method of repeating the operation of adding and mixing the organic solvent after removing (). When a water-soluble organic solvent having a boiling point higher than that of water is used, water may be removed by distillation (including azeotropic distillation) to replace the solvent.

Examples of the water-soluble organic solvent include alcohols (C _1-4 alkanols such as methanol, ethanol, propanol, and isopropanol), ethers (cyclic ethers such as dioxane and tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene). (Poly) oxyethylene glycol diC _1-4 alkyl ether such as glycol dimethyl ether), ketones (such as acetone), amides (such as dimethylformamide, diethylformamide, dimethylacetamide, and diethylacetamide), sulfoxides (such as dimethyl sulfoxide) ), alkane diols (e.g., ethylene glycol, _{C 2-4} alkane diols, such as propylene glycol), Serosoru S (methyl cellosolve, ethyl cellosolve), (such as ethyl carbitol) carbitol, carbonates (ethylene carbonate, propylene carbonate, and dimethyl carbonate) and the like. These solvents may be used alone or in combination of two or more.

  In the cellulose fiber-containing dispersion liquid that has been solvent-substituted with a water-soluble organic solvent, the water-soluble organic solvent can be replaced with a non-water-soluble organic solvent in the same manner as above. Examples of the non-water-soluble organic solvent include ethers (dialkyl ether such as diethyl ether and diisopropyl ether), esters (methyl acetate, ethyl acetate, butyl acetate, etc.), ketones (methyl ethyl ketone, methyl isobutyl ketone, etc.), nitrile (Acetonitrile, benzonitrile, etc.), cellosolve acetates, carbitol acetates, hydrocarbons (aliphatic hydrocarbons such as hexane, octane, cyclohexane, aromatic hydrocarbons such as toluene), halogenated hydrocarbons (Dichloromethane, chloroform, carbon tetrachloride, dichloroethane, trichloroethylene, etc.) can be exemplified. These water-insoluble organic solvents can also be used alone or in combination of two or more.

  The solid content concentration of the cellulose fiber in the dispersion liquid is, for example, 0.01 to 30% by weight (for example, 0.1 to 20% by weight), preferably 1 to 15% by weight, and more preferably 3 to 12% by weight ( For example, it may be about 5 to 10% by weight. If the solid content concentration is too low, the reaction efficiency may decrease.

  The reaction may be carried out under reduced pressure, but is usually carried out under pressure or normal pressure. The reaction temperature can be appropriately selected depending on the boiling point of the solvent and the like, and may be, for example, about 50 to 200 ° C (eg, 70 to 170 ° C), preferably about 80 to 150 ° C (eg, 100 to 130 ° C). The reaction may be performed under reflux of the solvent. The reaction time is not particularly limited and is, for example, about 10 minutes to 48 hours (for example, 30 minutes to 24 hours). Further, the reaction can be carried out in air or in an atmosphere of an inert gas (a rare gas such as nitrogen or argon) with stirring.

  The reaction may be carried out while stirring the reaction system, or may be carried out while subjecting the cellulose fibers to mechanical shearing force to micronize the cellulose fibers to obtain modified cellulose fibers. Further, the modified cellulose fibers may be pulverized by defibrating after the reaction. In the miniaturization step, the cellulose fibers may be reacted while being miniaturized into nanofibers, or the modified cellulose fibers produced by the reaction may be miniaturized into nanofibers.

  The modified cellulose fiber produced by the reaction may be separated and purified by a conventional method (for example, centrifugation, filtration, concentration, extraction, etc.). For example, a solvent capable of dissolving at least the phenolic fluorene compound is added to the reaction mixture, the unreacted phenolic fluorene compound is removed by a separation method (conventional method) such as centrifugation, filtration, or extraction described above, followed by separation and purification. May be. The above separating operation can be performed multiple times (for example, about 2 to 5 times). Further, the modified cellulose fiber separated and purified may be dried under heating or under reduced pressure or under normal pressure to obtain a modified cellulose fiber having a powdery form.

  Incidentally, the modified cellulose fiber purified by repeatedly removing the unreacted phenolic fluorene compound by the above separation method, when analyzed by a method such as Raman analysis, there is a peak derived from the cellulose fiber and a peak derived from the fluorene compound. However, it can be confirmed that the phenolic fluorene compound is bonded to the cellulose fiber.

  The modified cellulose fiber thus obtained has higher dispersion stability in an organic solvent than the unmodified cellulose fiber. Therefore, the dispersion liquid in which the modified cellulose fiber is dispersed in the organic solvent can be easily added to the coating agent, the paint, etc., and the characteristics of the coating film can be improved.

[Resin composition]
Since the modified cellulose fiber of the present invention has excellent affinity or miscibility with a resin, it can be used as a resin composite material (for example, a reinforcing material).

  The resin may be either a thermoplastic resin or a thermosetting resin. Examples of the thermoplastic resin include olefin resins (polyethylene, polypropylene, polymethylpentene, amorphous polyolefin, etc.), vinyl resins (acrylic resins such as polymethyl methacrylate), styrene resins such as polystyrene and acrylonitrile-styrene resin. Resin, polyvinyl chloride, etc., polycarbonate resin (bisphenol A type polycarbonate, etc.), polyester resin [polyethylene terephthalate, polybutylene terephthalate, polycyclohexane dimethylene terephthalate, polyalkylene arylate such as polyethylene naphthalate, polyarylate, liquid crystal polyester, fat Group polyesters (polylactic acid, polycaprolactone, polyethylene adipate, polybutylene adipate, etc.)], polyacetal Oil, polyamide resin (nylon 6, nylon 66, nylon 46, nylon 6T, nylon MXD, etc.), polyphenylene ether resin (modified polyphenylene ether, etc.), polysulfone resin (polysulfone, polyether sulfone, etc.), polyphenylene sulfide resin, thermoplastic polyimide Examples thereof include resins (polyether imide, polyamide imide, polyamino bismaleimide, etc.), polyether ketone resins (polyether ketone, polyether ether ketone, etc.), thermoplastic elastomers, and fluororesins. Examples of the thermosetting resin include phenol resin, amino resin (urea resin, melamine resin, furan resin, etc.), unsaturated polyester, diallyl phthalate resin, vinyl ester resin, epoxy resin, urethane resin, silicone resin, thermosetting resin. Examples of the resin include a polyimide resin. These resins can be used alone or in combination of two or more. Further, the resin may be, for example, a water-soluble resin such as polyvinyl alcohol or cellulose ether, a water-dispersible resin such as an acrylic resin emulsion, an ethylene-vinyl acetate copolymer emulsion, or a styrene resin emulsion.

  From the viewpoint of reducing the environmental load, a biomass-derived aliphatic polyester resin, such as polylactic acid, may be used. Note that polylactic acid has a limitation such as low heat resistance, but the modified cellulose fiber of the present invention has good miscibility with polylactic acid and can supplement defects such as heat resistance.

  The proportion of the modified cellulose fiber is, for example, 0.1 to 50 parts by weight (for example, 0.5 to 40 parts by weight), preferably 1 to 30 parts by weight (for example, 3 to 20 parts by weight) with respect to 100 parts by weight of the resin. Parts), more preferably about 5 to 15 parts by weight (for example, 7 to 12 parts by weight). If the proportion of the modified cellulose fiber is too small, the reinforcing property with respect to the resin may decrease, and if it is too large, the miscibility and moldability may decrease.

  The resin composition can be prepared by a conventional method such as a melt kneading method. Since the modified cellulose fiber of the present invention can be mixed with the resin (even in a dry state) without being used in the form of a dispersion liquid, a method of mechanically melt-kneading (or mixing) can be preferably used. In the melt-kneading, the modified cellulose fiber is mixed with the molten resin in a fibrous form without melting.

  Melt-kneading can be performed by a conventional method, for example, a mixing roller, a kneader, a Banbury mixer, an extruder (a single-screw or a twin-screw extruder, etc.). The temperature of the melt-kneading can be appropriately selected according to the melting characteristics of the resin, and is usually lower than the decomposition start temperature and higher than the melt start temperature. For example, the temperature may be 100 to 300 ° C, preferably 130 to 260 ° C (for example, 150 to 250 ° C), and more preferably 170 to 230 ° C.

  The resin composition may be obtained by directly melt-kneading the resin and the modified cellulose fiber at a predetermined ratio, and the content of the modified cellulose fiber by melt-kneading the master batch containing the modified cellulose fiber and the resin. You may adjust.

  The masterbatch may be prepared by melt-kneading a resin and modified cellulose fiber at a high modified cellulose fiber concentration, or may be prepared by using a solvent. The solvent can be selected according to the type of resin, and may be a solvent in which the resin is soluble. Such a solvent may be the water-soluble organic solvent or non-water-soluble organic solvent exemplified above, and when using a water-soluble resin or a water-dispersible resin, the solvent may be water. When preparing a masterbatch using an organic solvent, a mixed solution containing a resin, a solvent in which this resin is soluble, and modified cellulose fibers is prepared, and if necessary, a dispersion mixer (ultrasonic disperser, disper, etc.) Alternatively, the solvent may be removed by dispersing and mixing. In addition, you may mix the resin solution which melt | dissolved resin in the solvent, and the modified cellulose fiber. More specifically, a masterbatch is prepared by removing the solvent from a uniform mixture of a dispersion of modified cellulose fibers dispersed in a solvent (particularly in an organic solvent), a resin, and a solvent in which the resin is soluble. You may. The masterbatch may be in the form of pellets or powder.

  In the masterbatch, the proportion of the modified cellulose fiber is, for example, 1 to 70 parts by weight (eg, 5 to 65 parts by weight), preferably 10 to 60 parts by weight, and more preferably 20 to 50 parts by weight with respect to 100 parts by weight of the resin. It may be about parts by weight (for example, 30 to 45 parts by weight).

  Further, the resin composition can be molded by a conventional molding method (for example, compression molding, injection molding, extrusion molding, etc.). In particular, if injection molding or extrusion molding is used, the productivity of molded products can be improved.

  The resin composition includes various additives such as stabilizers (antioxidants, ultraviolet absorbers, light stabilizers, heat stabilizers, etc.), antistatic agents, flame retardants (phosphorus flame retardants, Halogen-based flame retardants, inorganic flame retardants, etc.), flame retardant aids, impact modifiers, fluidity improvers, reinforcing materials (fillers, etc.), nucleating agents, colorants, lubricants, plasticizers, release agents, It may contain a hue improver, a dispersant, an antibacterial agent, a preservative and the like. When the resin is a thermosetting resin, the resin composition may contain a curing agent, a curing accelerator, and the like.

  The resin composition (composite material) of the present invention can be reinforced with modified cellulose fibers, and has characteristics such as high strength, high elastic modulus, high heat resistance, and low linear expansion characteristics. Furthermore, when a modified cellulose fiber having a nanometer size (for example, cellulose nanofiber) is used, the light scattering property in the visible light wavelength region is low, and the resin composition is also excellent in transparency. For example, when a modified cellulose fiber having a nanometer size is contained at a ratio of 10% by weight and a film having a thickness of 30 μm is formed, the total light transmittance is, for example, 30% or more (for example, 40 to 99%), preferably 50%. It may be about (for example, 60 to 98%), more preferably about 60% or more (for example, 70 to 95%), or about 60 to 90% (for example, 70 to 85%).

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

  The modified cellulose nanofibers prepared in Example 1 had the 9,9-bis [4-hydroxyphenyl] fluorene (hereinafter referred to as BPF) modification rate (BPF modification rate), shape, and crystallinity as follows. Measured or evaluated.

(Ratio of fluorene compound bonded to cellulose (modification rate))
The modification rate of the fluorene compound was quantified by FT-Raman analysis. Cellulose acetate (manufactured by Daicel Corp.) and a predetermined amount of 9,9-bis (4-hydroxyphenyl) fluorene (hereinafter referred to as BPF) were dissolved in tetrahydrofuran (THF) to form a film, and a Raman microscope (Horiba Jobin Raman analysis was performed using "XploRA" manufactured by YVON. Aromatic ring (1604cm ^-1) and the intensity ratio of the absorption band of cellulose endocyclic CH (1375 cm ^-1) and _{(I 1604} / _{I 1375),} based on the concentration of the BPF, a calibration curve was prepared. All samples were measured in triplicate and the results were averaged.

(Solvent dispersibility)
A predetermined amount of cellulose fiber was dispersed in tetrahydrofuran to prepare a 0.2 wt% cellulose fiber dispersion, which was left at room temperature and the dispersibility was evaluated based on the sedimentation time.

Example 1
(1) Preparation of Cellulose-Containing Solvent Dispersion System 100 g (solid content 15 g) of an aqueous dispersion “Cellish” of cellulose fibers (“KY110N” manufactured by Daicel Finechem Ltd., cellulose: water (weight ratio) = 15/85) After dispersing in 500 g of triethylene glycol dimethyl ether (hereinafter, TEGDME) and centrifuging, the operation of dispersing the precipitated solid content in 500 g of TEGDME was repeated three times, and the dispersion liquid in which water as a solvent was replaced with TEGDME ( A concentration of cellulose fibers of 20% by weight) was obtained.

(2) Reaction with phenolic fluorene compound 5 g of the obtained dispersion was mixed with a predetermined amount of TEGDME and azobisisobutyronitrile (AIBN) as a radical initiator, and TEGDME 27 was added to 1 g of cellulose fiber. A mixed liquid of 0.5 g and a radical activator of 2.0 g was prepared, and the mixed liquid was heated to 100 ° C. under an argon atmosphere to start the reaction, and stirred for 6 hours. 10 minutes after the start of the reaction, a solution containing 5.0 g of 9,9-bis (4-hydroxyphenyl) fluorene (manufactured by Osaka Gas Chemicals Co., Ltd., referred to as BPF) and 15 g of TEGDME was added dropwise over 3 minutes. After completion of the reaction, the reaction product was filtered and washed with tetrahydrofuran three times to remove unreacted BPF and radical initiator to obtain a modified cellulose fiber (nanofiber).

  When the BPF modification rate was determined, the modification rate was 3.9 mmol / 100 g (1.4% by weight). In addition, when the shape of the modified cellulose fiber was observed using FE-SEM (“JSM-6700F” manufactured by JEOL Ltd., measurement condition: 20 mA, 60 seconds), the fiber diameter of the modified cellulose nanofiber (CNF) was observed. (Or diameter) is about 10 to 550 nm, and when 50 fibers are randomly selected from the image of the SEM photograph and the average fiber diameter is calculated by averaging, the average fiber diameter was 33 nm.

  Furthermore, as a result of evaluating the dispersibility in tetrahydrofuran (settling time), as shown in FIG. 1, the modified cellulose fibers (nanofibers) hardly sedimented even after 24 hours or more, and the supernatant was slight.

Comparative Example 1
A mixed solution containing cellulose fibers, TEGDME, and BPF was prepared in the same ratio as in Example 1 without using a radical initiator, and stirred under heating in the same manner as in Example 1. When the cellulose fibers were separated in the same manner as in Example 1, the cellulose fibers were not modified with the phenolic fluorene compound at all. Further, as a result of evaluating dispersibility in tetrahydrofuran (sedimentation time), as shown in FIG. 1, after 24 hours or more, most of the cellulose fibers were sedimented and a supernatant was formed.

  Since the modified cellulose fiber of the present invention has excellent dispersibility in a resin, it can be used for a wide range of applications, resin reinforcing materials, additives, materials for films and sheets, and the like. In addition, since the resin composition (composite material) has excellent characteristics such as low linear expansion characteristics, high strength, and high elastic modulus, and high thermal deformation resistance, for example, various resin molded products, liquid crystal display substrates, It is useful as various materials such as solar cell substrates and automobile panels.

  Furthermore, the modified cellulose fiber is added to an optical resin (or a transparent resin such as an acrylic resin, a polycarbonate resin, a cyclic olefin resin, a cellulose acylate resin such as cellulose diacetate, or cellulose triacetate) and oriented. Even if it is highly transparent, an optical film or an optical sheet, for example, a polarizing film (and a polarizing plate protective film), a retardation film (for example, a retardation film having a reverse wavelength dispersion property), an alignment film (alignment film), a visual field. It can also be used as an angle expansion (compensation) film, a diffusion plate (film), and the like.

Claims (10)

Modified cellulose fibers obtained by reacting radically activated cellulose fibers with a compound having a 9,9-bisarylfluorene skeleton represented by the following formula (1) in a solvent.
(In the formula, ring Z is an arene ring; n is an integer of 1 or more; R ¹ and R ² are substituents; p is 0 or an integer of 1 or more; k is an integer of 0 to 4) In formula (1), ring Z is a monocyclic arene ring, a polycyclic arene ring or a ring-collecting arene ring, n is an integer of 1 to 3 independently, R ¹ is an alkyl group or an alkoxy group, p Is an integer of 0 to 3, R ² is a cyano group, a halogen atom or an alkyl group, and k is an integer of 0 to ^3. The modified cellulose fiber according to claim 1. In the formula (1), the ring Z is a benzene ring, a naphthalene ring or a biphenyl ring, n is 1 or 2, R ¹ is a C _1-4 alkyl group, p is an integer of 0 to 2, R ² is C _1-. The modified cellulose fiber according to claim 1 or 2, wherein ₄ alkyl groups and k are 0 or 1.   The modification according to any one of claims 1 to 3, wherein the ratio of the compound represented by the formula (1) bonded to the cellulose fiber is 0.01 to 20% by weight based on the total amount of the modified cellulose fiber. Cellulose fiber.   The modified cellulose fiber according to any one of claims 1 to 4, which is a nanofiber.   The modified cellulose fiber according to any one of claims 1 to 5, which has an average fiber diameter of 5 to 500 nm.   The modified cellulose fiber according to any one of claims 1 to 6, which is a resin reinforcing material.   A resin composition comprising the modified cellulose fiber according to claim 1.   The modified cellulose fiber according to claim 1, wherein the cellulose fiber is heat-treated in a solvent in the presence of a radical generator to react with the compound represented by the formula (1) according to claim 1. A method of manufacturing.   The method according to claim 9, wherein the cellulose fibers include nanocellulose fibers derived from at least one pulp selected from wood pulp and cotton linter pulp.