Fiber composite material and its manufacturing method

Abstract

To provide a bamboo fiber composite that is a composite of bamboo fiber with fluorene-modified cellulose nanofiber (FCNF) comprising a cardo structure-bearing fluorene derivative as a binder.SOLUTION: Bamboo fiber (a) alkali-treated with a sodium hydroxide solution is oriented in one direction (b); the oriented bamboo fiber is coated with fluorene-modified cellulose nanofiber, with the weight proportion of the mixed cellulose nanofiber to the bamboo fiber being 2.5-10%; and finally the coated bamboo fiber is hot-press molded at 180-250°C, to prepare a bamboo fiber composite. There is also provided a method for producing the same.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fiber composite material using cellulose nanofiber (CNF) as a binder and a method for producing the same. [Background technology]

[0002] In recent years, research on biodegradable composite materials known as green composites, which are made by mixing biodegradable resins with plant-derived biomass, has been attracting attention, and fiber-reinforced composite materials are used in structural applications such as interior parts for automobiles and aircraft, where improved fuel efficiency through weight reduction is required. In particular, carbon fiber composites have the potential to reduce the weight of aircraft parts by up to 40% compared to light metal alloys, with aircraft such as the Airbus A380 and Boeing 787 Dreamliner achieving at least 25% structural mass savings by replacing metal alloys with composites. Applications of fiber-reinforced composites are increasing in sporting goods, electronic devices, and various home appliances, but they also show promise in the fields of orthopedic medicine and prosthetics, so research into them is being actively conducted. Natural fibers and synthetic polymers used as composite materials are also used in automobile parts, mobile phones, and other applications.

[0003] Nature is rich in fibers that have been used since ancient times, such as bagasse, bamboo, coir, flax, hemp, jute, and sisal. The inventor developed a fiber composite material using bamboo, a fast-growing grass that grows in tropical and subtropical regions and has high mechanical properties with an intrinsic strength of 300-600 MPa and a tensile modulus of 20-50 GPa, as well as excellent temperature stability.

[0004] Patent Document 1 discloses a polyamide composition and a method for producing the same, which is a modified cellulose nanofiber bonded with a compound having a fluorene skeleton, and which can improve the lightness and mechanical properties at high temperatures. The document also discloses "bamboo" as an example of a cellulose nanofiber that is chemically modified with a fluorene compound. However, the mechanical properties of composite materials produced by using bamboo fibers and fluorene-modified cellulose nanofibers (FCNF) made from fluorene derivatives with a cardo structure as a binder have not been clarified. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP2019-001854A Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the objective of this invention is to clarify the mechanical properties of a composite material produced by using bamboo fibers and fluorene-modified cellulose nanofiber (FCNF) made from a fluorene derivative with a cardo structure as a binder, and to demonstrate its industrial applicability. [Means for solving the problem]

[0007] In this study, we compared composite materials produced using three types of binders: cellulose nanofiber (CNF), carbon nanofiber (CBF) made from finely ground bamboo fiber, and fluorene-modified cellulose nanofiber (FCNF) made from a fluorene derivative with a cardo structure, with bamboo fiber.

[0008] As a result, it was found that the FCNF bamboo fiber composite using fluorene-modified cellulose nanofiber (FCNF) with a fluorene derivative having a cardo structure as a binder showed the highest bending strength among the three types of binders. This result was presumed to be due to the strong bonding between the bamboo fibers and the fluorene-modified cellulose nanofibers (FCNFs) caused by a chemical reaction.

[0009] They then investigated the effect of fiber orientation accuracy on the mechanical properties of the composite material, and found that when the bamboo fibers were oriented in one direction so that they did not cross each other, the mechanical properties were approximately twice as good as those of a composite material in which the fibers crossed each other. In addition, when the fibers were oriented in one direction so that they did not cross each other, the cross section of the fibers was significantly deformed by the compressive stress during hot press molding, reducing the gaps between the fibers and improving the adhesion at the interface.

[0010] Furthermore, it was found that the maximum elastic modulus and strength of a composite material made of fluorene-modified cellulose nanofiber (FCNF), a compound represented by the following chemical formula 6 in which one of the epoxy groups is reacted with the hydroxyl group of cellulose using a fluorene derivative with a cardo structure, a compound represented by the following chemical formula 5, and bamboo fiber, are around 230 to 250°C, and that at temperatures above 270°C, the mechanical properties rapidly decrease due to thermal degradation of the bamboo fiber. [ka] [ka]

[0011] As such, fluorene-modified cellulose nanofibers (FCNF) made from fluorene derivatives with a cardo structure have high dispersibility and compatibility with resins, and have potential as reinforcing agents for green composites. Therefore, we developed a composite material of fluorene-modified cellulose nanofibers (FCNF) made from fluorene derivatives with a cardo structure and bamboo fiber.

[0012] (Compounds having a fluorene skeleton) Fluorene compounds have a 9,9-bisarylfluorene skeleton and a carboxyl group. or Epoxy groups are selected from the group consisting of R The carboxyl group has at least one reactive group. AsExamples of the epoxy group include an alkoxycarbonyl group (e.g., a C1-4 alkoxy-carbonyl group such as a methoxycarbonyl group or an ethoxycarbonyl group), an acid halide group (e.g., an acid chloride group or an acid bromide group, a haloformyl group), etc. The epoxy group may be a glycidyl group as long as it contains an oxirane ring. Such fluorene compounds include, for example, 9,9-bisaryl-2,7-dicarboxyfluorene. or It may be 9,9-bisaryl-2,7-di(glycidyl ester)fluorene or the like.

[0013] A typical fluorene compound is represented by the following formula 7. [ka] [In the formula (1), ring Z is an arene ring, X is a group represented by the formula (2-1) or (2-2) in the following formula (8), n is an integer of 1 to 3, R 3 and R 4 represents a substituent, p represents an integer of 0 or 1 or more, and k represents an integer of 0 to 4. [ka] [R 1 is a hydrogen atom or an alkyl group, R 2 represents an alkylene group, m1 represents an integer of 0 or 1 or more, and m2 represents an integer of 0 or 1 or more.

[0014] In the above-mentioned "Chemical Formula 7" (1), examples of the arene ring represented by ring Z include monocyclic arene rings such as a benzene ring, and polycyclic arene rings. The polycyclic arene rings include fused polycyclic arene rings (fused polycyclic hydrocarbon rings) and ring-assembled arene rings (ring-assembled aromatic hydrocarbon rings).

[0015] The fused polycyclic arene rings include, for example, fused bicyclic arenes (e.g., fused bicyclic C such as naphthalene). 10-16Examples of the fused polycyclic arene ring include a fused bicyclic to tetracyclic arene ring such as a fused tricyclic arene (e.g., anthracene, phenanthrene, etc.) ring. Examples of the fused polycyclic arene ring include a naphthalene ring and an anthracene ring, and a naphthalene ring is particularly preferred. The two rings Z may be the same or different rings.

[0016] Examples of the ring assembly arene ring include biarene rings, such as biphenyl rings, binaphthyl rings, and phenylnaphthalene rings (1-phenylnaphthalene rings, 2-phenylnaphthalene rings, etc.). 6-12 Arene rings, terarene rings, e.g., terphenylene rings, etc. 6-12 Examples of the preferred ring assembly arene rings include biC 6-10 Examples include an arene ring, particularly a biphenyl ring.

[0017] In the above "Chemical Formula 7" (1), R 1 The alkyl group represented by the formula (I) is a straight-chain or branched C alkyl group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, or a t-butyl group. 1-6 Examples of the alkyl group include the alkyl group C 1-4 Alkyl groups, especially C 1-2 It is an alkyl group. m1 may be 0 or an integer of 1 or more (for example, about 1 to 6, preferably about 1 to 4, and more preferably about 1 to 2). m1 may usually be 0 or 1 to 2.

[0018] Alkylene group R 2 includes linear or branched alkylene groups, and examples of the linear alkylene group include C alkylene groups such as ethylene, trimethylene, and tetramethylene. 2-6 Alkylene group (preferably linear C 2-4 Alkylene groups, more preferably linear C 2-3 Examples of the branched alkylene group include branched C alkylene groups such as propylene, 1,2-butanediyl, and 1,3-butanediyl. 3-6 Alkylene group (preferably branched C 3-4alkylene groups, particularly propylene groups).

[0019] Oxyalkylene group (OR 2 The number m2 of 0 or 1 or more can be selected from the range of about an integer (for example, 0 to 15, preferably 0 to 10), and may be, for example, about 0 to 8 (for example, 1 to 8), preferably 0 to 5 (for example, 1 to 5), more preferably 0 to 4 (for example, 1 to 4), particularly preferably about 0 to 3 (for example, 1 to 3), and may usually be 0 to 2 (for example, 0 or 1). When m2 is 2 or more, the number of alkylene groups R 2 The types of the substituents R may be the same or different. 2 The types of may be the same or different in the same or different rings Z.

[0020] In the above formula (1), the number of substitutions n in the group X may be the same or different depending on the type of ring Z, and may be an integer of 1 or more, for example, 1 to 4, preferably 1 to 3, more preferably 1 or 2, and particularly preferably 1. The number of substitutions n in each ring Z may be the same or different.

[0021] In addition, the group X can be substituted at an appropriate position of the ring Z. For example, when the ring Z is a benzene ring, it is often substituted at the 2-, 3-, and 4-positions (particularly, the 3- and / or 4-positions) of the phenyl group. When the ring Z is a naphthalene ring, it is often substituted at the 5- to 8-positions of the naphthyl group. For example, the 1- or 2-position of the naphthalene ring is substituted with respect to the 9-position of the fluorene (substitution in a 1-naphthyl or 2-naphthyl relationship), and the group X is often substituted with respect to this substitution position in a 1,5- or 2,6-position relationship (particularly, when n is 1, 2,6-position relationship). In addition, when n is 2 or more, the substitution position is not particularly limited. In addition, in the ring assembly arene ring Z, the substitution position of the group X is not particularly limited, and for example, it may be substituted on the arene ring bonded to the 9-position of the fluorene and / or the arene ring adjacent to this arene ring. For example, the 3- or 4-position of the biphenyl ring Z may be bonded to the 9-position of the fluorene, and when the 4-position of the biphenyl ring Z is bonded to the 9-position of the fluorene, the substitution position of the group X may be any of the 2-, 3-, 2'-, 3'- or 4'-position, and is usually the 2-, 3'- or 4'-position, preferably the 2- or 4'-position (particularly the 2-position).

[0022] In the above "Chemical Formula 7" (1), the substituent R 3 Examples of the alkyl group include linear or branched C alkyl groups such as halogen atoms (e.g., fluorine, chlorine, bromine, and iodine atoms), alkyl groups (methyl, ethyl, propyl, isopropyl, butyl, s-butyl, and t-butyl groups), and the like. 1-10 Alkyl groups, preferably linear or branched C 1-6 Alkyl groups, more preferably linear or branched C 1-4 alkyl group, cycloalkyl group (cyclopentyl group, cyclohexyl group, etc.) 5-10 Cycloalkyl groups, aryl groups [phenyl groups, alkylphenyl groups (methylphenyl (tolyl) groups, dimethylphenyl (xylyl) groups, etc.), biphenyl groups, naphthyl groups, etc. 6-12 aryl group], aralkyl group (benzyl group, phenethyl group, etc.) 6-10 Aryl-C 1-4Alkyl groups, etc.), alkoxy groups (e.g., methoxy groups, ethoxy groups, propoxy groups, n-butoxy groups, isobutoxy groups, t-butoxy groups, and other linear or branched C 1-10 alkoxy groups, cycloalkoxy groups (e.g., cyclohexyloxy groups, etc.) 5-10 cycloalkyloxy groups, aryloxy groups (e.g., phenoxy groups, etc.) 6-10 aryloxy groups, aralkyloxy groups (e.g., C 6-10 Aryl-C 1-4 alkyloxy groups, alkylthio groups (e.g., methylthio, ethylthio, propylthio, n-butylthio, t-butylthio, etc.) 1-10 alkylthio groups, cycloalkylthio groups (e.g., cyclohexylthio groups, etc.) 5-10 cycloalkylthio groups, arylthio groups (e.g., thiophenoxy groups, etc.) 6-10 arylthio groups, aralkylthio groups (e.g., benzylthio groups, etc.) 6-10 Aryl-C 1-4 alkylthio groups, acyl groups (e.g., acetyl groups, etc.) 1-6 acyl group, carboxyl group, alkoxycarbonyl group (e.g., methoxycarbonyl group, etc.) 1-4 Alkoxy-carbonyl group, nitro group, cyano group, dialkylamino group (e.g., di-C such as dimethylamino group) 1-4 alkylamino groups, dialkylcarbonylamino groups (e.g., diacetylamino groups, etc.) 1-4 Alkyl-carbonylamino groups, etc. can be mentioned.

[0023] These substituents R 3 Representative examples of the substituent R include a halogen atom, a hydrocarbon group (an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group), an alkoxy group, an acyl group, a nitro group, a cyano group, and a substituted amino group. 3 As the alkyl group, linear or branched C 1-4Alkoxy groups, in particular linear or branched C alkyl groups such as alkyl groups (especially methyl groups) 1-4 The substituent R is preferably an alkyl group. 3 is an aryl group, the substituent R 3 may form the ring assembly arene ring together with the ring Z. 3 The types of may be the same or different in the same or different rings Z.

[0024] Substituent R 3 The coefficient p can be appropriately selected depending on the type of ring Z, and may be, for example, an integer of about 0 to 8, an integer of 0 to 4, preferably an integer of 0 to 3 (e.g., 0 to 2), and particularly 0 or 1. In particular, when p is 1, the ring Z is a benzene ring, a naphthalene ring, or a biphenyl ring, the substituent R 3 may be a methyl group.

[0025] Substituent R 4 As the alkyl group, a cyano group, a halogen atom (such as a fluorine atom, a chlorine atom, or a bromine atom), a carboxyl group, an alkoxycarbonyl group (such as a methoxycarbonyl group) 1-4 Alkoxy-carbonyl group, alkyl group (methyl group, ethyl group, propyl group, isopropyl group, butyl group, t-butyl group, etc.) 1-6 C alkyl groups, aryl groups (phenyl groups, etc. 6-10 Aryl groups).

[0026] These substituents R 4 Of these, linear or branched C 1-4 Alkyl groups (especially C groups such as methyl groups) 1-3 alkyl group), carboxyl group or C 1-2 An alkoxy-carbonyl group, a cyano group, or a halogen atom is preferred. The number of substitutions k is an integer of 0 to 4 (e.g., 0 to 3), preferably an integer of 0 to 2 (e.g., 0 or 1), particularly 0. The numbers of substitutions k may be the same or different from each other, and when k is 2 or more, the substituent R 4 The types of the substituents R substituted on the two benzene rings of the fluorene ring may be the same or different.4 The types of the substituents R may be the same or different. 4 The substitution position of is not particularly limited, and may be, for example, the 2-position to the 7-position (such as the 2-position, the 3-position, and / or the 7-position) of the fluorene ring.

[0027] Specific examples of fluorene compounds having the group X represented by "Chemical formula 8" (2-1) include 9,9-bis(carboxyaryl)fluorenes in which n=1, p=k=0, and m1=0, such as 9,9-bis(carboxyaryl)fluorenes, such as 9,9-bis(3-carboxyphenyl)fluorene, 9,9-bis(4-carboxyphenyl)fluorene, 9,9-bis(5-carboxynaphthyl)fluorene, and 9,9-bis(6-carboxynaphthyl)fluorene. 6-10 aryl)fluorene; 9,9-bis(carboxyalkyl-aryl)fluorene compounds in which n=1, p=k=0, and m1=1 to 3, such as 9,9-bis(4-(carboxymethyl)phenyl)fluorene, 9,9-bis(4-(2-carboxyethyl)phenyl)fluorene, 9,9-bis(3-(carboxymethyl)phenyl)fluorene, 9,9-bis(5-(carboxymethyl)naphthyl)fluorene, and 9,9-bis(6-(carboxymethyl)naphthyl)fluorene. 1-6 Alkyl C 6-10 aryl)fluorene, etc. These fluorene compounds can be used alone or in combination of two or more kinds.

[0028] Specific examples of fluorene compounds having the group X represented by "Chemical Formula 8" (2-2) include 9,9-bis(glycisyloxyaryl)fluorenes in which n = 1, p = k = 0, and m2 = 0, such as 9,9-bis(glycisyloxyphenyl)fluorene, 9,9-bis(4-glycisyloxyphenyl)fluorene, 9,9-bis(5-glycisyloxynaphthyl)fluorene, and 9,9-bis(6-glycisyloxynaphthyl)fluorene. 6-10aryl)fluorene; 9,9-bis(glycisyloxy(poly)alkoxyaryl)fluorenes in which n=1, p=k=0, and m2=1 to 5, such as 9,9-bis(4-(2-glycisyloxyethoxy)phenyl)fluorene, 9,9-bis(4-(2-glycisyloxypropoxy)phenyl)fluorene, 9,9-bis(5-(2-glycisyloxyethoxy)naphthyl)fluorene, and 9,9-bis(6-(2-glycisyloxyethoxy)naphthyl)fluorene. 2-4 Alkoxy C 6-10 aryl)fluorene; 9,9-bis(alkyl-glycidyloxyaryl)fluorenes, such as 9,9-bis(3-methyl-4-glycidyloxyphenyl)fluorene, in which n=1, p=1, k=0, and m2=0; 1-4 Alkyl-glycyloxy C 6-10 aryl)fluorene; 9,9-bis(alkyl-glycidyloxy(poly)alkoxyaryl)fluorenes, where n=1, p=1, k=0, and m2=1 to 5, such as 9,9-bis(3-methyl-4-(2-glycidyloxyethoxy)phenyl)fluorene; 1-4 Alkyl-glycyloxy(poly)C 2-4 Alkoxy C 6-10 aryl)fluorene; 9,9-bis(aryl-glycidyloxyaryl)fluorene, where n=1, p=0, k=0, and m2=0, such as 9,9-bis(4-phenyl-3-glycidyloxyphenyl)fluorene; 6-10 Aryl-glycidyloxy C 6-10 aryl)fluorene; 9,9-bis(aryl-glycidyloxy(poly)alkoxyaryl)fluorenes, where n=1, p=0, k=0, and m2=1 to 5, such as 9,9-bis(4-phenyl-3-(2-glycidyloxyethoxy)phenyl)fluorene; 6-10 Aryl-glycidyloxy(poly)C 2-4 Alkoxy C 6-109,9-bis(di(glycidyloxy)aryl)fluorene, where n=2, p=0, k=0, and m2=0, such as 9,9-bis(di(glycidyloxy)aryl)fluorene, e.g., 9,9-bis(di(glycidyloxy)C, such as 9,9-bis(3,4-di(glycidyloxy)phenyl)fluorene; 6-10 9,9-bis(di(glycidyloxy(poly)alkoxy)aryl)fluorenes, such as 9,9-bis(di(glycidyloxy(poly)alkoxy)aryl)fluorene, where n=2, p=0, k=0, and m2=1 to 5, for example, 9,9-bis(di(glycidyloxy(poly)alkoxy)aryl)fluorene. 2-4 Alkoxy)C 6-10 aryl)fluorene, etc. These fluorene compounds can be used alone or in combination of two or more kinds.

[0029] The fluorene compound having a group represented by (2-2) in the above "Chemical Formula 8" may be a monomer or a polymer (e.g., a dimer, a trimer, etc.). The fluorene compound having a glycidyl group usually contains at least a monomer, and may be, for example, a mixture of a monomer, a dimer, and a trimer.

[0030] A preferred fluorene compound is 9,9-bis(glycidyloxy C 6-10 aryl)fluorene, 9,9-bis(glycidyloxy(poly)C 2-4 Alkoxy C 6-10 aryl)fluorene, 9,9-bis(C 1-4 Alkyl-glycyloxy C 6-10 aryl)fluorene, 9,9-bis(C 1-4 Alkyl-glycyloxy(poly)C 2-4 Alkoxy C 6-10 aryl)fluorene, 9,9-bis(C 6-10 Aryl-glycidyloxy C 6-10 aryl)fluorene, 9,9-bis(C 6-10 Aryl-glycidyloxy(poly)C 2-4 Alkoxy C 6-10 The compound includes at least one monomer selected from the group consisting of aryl)fluorene and the like.

[0031] The fluorene compound having a group represented by (2-2) in the above "Chemical Formula 8", including a polymer, can be represented by the following "Chemical Formula 9". [ka] [In "Chemical formula 9", A represents a divalent group of "Chemical formula 10", q represents an integer of 0 or 1 or more, and the rings Z and R 2 ,m2,R 3 ,p,R 4 and k is the same as above. [ka]

[0032] The fluorene compound may be a commercially available product or may be prepared by a conventional method. For example, the fluorene compound having a group X represented by (2-1) in the above "Chemical Formula 8" can be prepared by reacting 9-fluorenones with an arene compound having a group X and a ring Z represented by (2-1) in the above "Chemical Formula 8". The fluorene compound having a group X represented by (2-2) in the above "Chemical Formula 8" can be prepared by reacting a group [HO-(R 2 O) m -] can be prepared by reacting substituted fluorenes with epichlorohydrin. Effect of the Invention

[0033] 1) By using fluorene-modified cellulose nanofiber (FCNF) as a binder, it is possible to obtain bamboo fiber composites with superior mechanical properties to those using cellulose nanofiber (CNF) or carbon nanofiber (CBF) made from finely ground bamboo fiber as a binder. 2) In addition, by orienting the bamboo fibers in one direction, it is possible to obtain a bamboo fiber composite with superior mechanical properties compared to a composite material made by simply smoothing the bamboo fibers and making them unaligned. 3) We can provide bamboo fiber composite materials with excellent mechanical properties that can be used in many applications, such as interior parts for automobiles and aircraft, where improved fuel efficiency through weight reduction is required. [Brief description of the drawings]

[0034] [Figure 1] Photographs of natural bamboo fibers obtained after alkali treatment (a) and unidirectionally oriented bamboo fibers before binder coating (b). [Diagram 2] Electron micrographs of cellulose fibers ((a) FCNF, (b) CBF, (c) CNF) [Diagram 3] Illustration of hot press molding of bamboo fiber and binder [Figure 4] A graph comparing the flexural modulus and strength of bamboo fiber composites with different binders [Diagram 5] Graph showing the relationship between displacement and load in bending test of bamboo fiber composite material [Figure 6] Micrographs of bamboo fiber composites ((a) CNF, (b) FCNF) [Figure 7] A graph comparing the flexural modulus and strength of unidirectionally oriented bamboo fiber composites and misaligned bamboo fiber composites that have only been smoothed. [Figure 8] Micrographs of unidirectionally aligned bamboo fibers after FCNF coating (a), misaligned bamboo fibers after just smoothing (b), the cross-section of the bamboo fiber composite after hot pressing (a) (c), and the cross-section of the bamboo fiber composite after hot pressing (b) (d). [Figure 9] A graph showing the relationship between hot pressing temperature and flexural modulus and strength of FCNF bamboo fiber composite material [Figure 10] A graph showing the bending modulus of unidirectionally oriented FCNF bamboo fiber composites when the mixed weight ratio of FCNF is changed. [Figure 11] A graph showing the strength of unidirectionally oriented FCNF bamboo fiber composites when the mixed weight ratio of FCNF is changed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] In this example, the culm used was a Moso bamboo that grows naturally in the western part of Tokushima Prefecture, and was approximately 15 m long, with the bottom 2 m or less of the culm being used. The internodes of the bamboo culms were cut to a length of 22 cm and the bark was peeled. The remaining bamboo after the bark was peeled was cut into 16 pieces that were radially symmetrical in shape from the cross section of the bamboo culm.

[0036] Each bamboo piece was treated with alkali by boiling it in a 3% by weight aqueous solution of sodium hydroxide (NaOH) at 80°C for 2 hours, and then the fibers were unraveled by hand until they reached the state shown in Figure 1(a). These fibers were approximately 22 cm long and 0.2-0.5 mm in diameter. These individual fibers are each made up of bundles of thin fibers with a diameter of about 0.01 to 0.015 mm, so strictly speaking they are "fiber bundles," but below they will be collectively referred to as "bamboo fiber."

[0037] Three types of binders were used: 9,9-bis(aryl)fluorene modified cellulose nanofiber (FCNF), cellulose nanofiber (CNF), and finely ground bamboo fiber (CBF). The respective electron microscope photographs are shown in Figure 2. The 9,9-bis(aryl)fluorene-modified cellulose nanofibers (FCNF) and cellulose nanofibers (CNF) used were provided in a dry state by Osaka Gas Chemicals Co., Ltd. Finely ground bamboo fiber (CBF) was prepared by diluting bamboo fiber immediately after alkali treatment with 200 mL of ion-exchanged water to a dilution weight ratio of 1:99, and grinding it in an electric juicer mixer.

[0038] 200 mL of ion-exchanged water was added to each binder at a dilution weight ratio of 1:99, and the mixture was mixed with a mechanical homogenizer at 8000 rpm for 20 minutes to obtain a suspension (diluted binder solution). To orient the bamboo fibers in one direction, 20 g of bamboo fibers were placed in a stainless steel tray, as shown in Figure 1(b), and the diluted binder solution was poured in. The stainless steel tray was then dried in an electric oven at 80°C for 24 hours.

[0039] Furthermore, since it had previously been confirmed that composite materials using unidirectionally oriented fibers exhibited bending strength that was 2.5 times higher than composite materials using discretely oriented fibers, particularly bamboo and kenaf, in this example, bamboo fibers oriented in one direction were used.

[0040] The bamboo fibers were dried and formed into a sheet (in this example, this state is referred to as "coating"), which was then laminated between stainless steel plates as shown in Figure 3, and hot pressed for 5 minutes at a mold temperature of 230°C and a pressure of 10 MPa. Then, the specimens were cut into test pieces measuring 13 mm in width and 29 mm in length using a diamond cutter, and bending tests were performed.

[0041] Bending tests were performed in accordance with ISO178 under the same conditions using a universal testing machine (Shimadzu Corporation, EZ-test, Japan) for each of the three bamboo fiber composites prepared with each of the three types of binder as test specimens. The bending strength was calculated using the maximum load during the bending test. The flexural modulus was calculated from the maximum value of the slope of the initial period (0 to 15% of the maximum load) of the load-displacement curve. The test conditions were a support distance of 22 mm and a crosshead speed of 1 mm / min. The test pieces used were 29 mm long, 13 mm wide, and 1.0 to 1.5 mm thick.

[0042] Figure 4 shows the flexural modulus and strength of bamboo fiber composites (hereinafter expressed as "XX (XX is the numerical value of the mixed weight ratio with bamboo fiber) % XX (XX is the name of the binder) bamboo fiber composite") containing three types of binders - 9,9-bis(aryl)fluorene-modified cellulose nanofiber (FCNF), cellulose nanofiber (CNF), and finely ground bamboo fiber (CBF) - at a mixed weight ratio of 10% with respect to the bamboo fiber. According to Figure 4, the 10% FCNF bamboo fiber composite had better mechanical properties than the other two binders.

[0043] FIG. 5 is a graph showing the relationship between load and displacement during bending tests of 10% FCNF bamboo fiber composite and 10% CNF bamboo fiber composite. The 10% FCNF bamboo fiber composite experienced fiber breakage at 215 MPa. On the other hand, delamination of the 10% CNF bamboo fiber composite began at 91 MPa.

[0044] Figure 6 shows micrographs of the surfaces of 10% FCNF bamboo fiber composite and 10% CNF bamboo fiber composite immediately after hot press molding at 230°C. As shown in Figure 6(a), some of the fibers in the bamboo fiber coated with CNF are not bonded and are separated from each other, whereas as shown in Figure 6(b), it can be seen that the binder and the bamboo fiber are integrated in the bamboo fiber coated with FCNF. This is presumably because the FCNFs having epoxy groups in the modified fluorene not only reacted with the hydroxyl groups of cellulose, but also reacted with each other to form bonds.

[0045] Figure 7 shows a comparison of the flexural modulus and strength of unidirectionally oriented 10% FCNF bamboo fiber composites and misaligned 10% FCNF bamboo fiber composites that were simply smoothed. The unidirectionally oriented 10% FCNF bamboo fiber composite had approximately twice the flexural modulus and strength as the misaligned 10% FCNF bamboo fiber composite that was simply smoothed.

[0046] The microstructure of the bamboo fiber composites was observed at both microscale (μm) and macroscale (mm). For micro-scale observation, a Hitachi High-Tech SEM-EDX (Miniscope (registered trademark) TM3030) was used. For macro-scale observation, a Keyence VHX-950F was used. The sample pieces were cut to a length of 10 mm, embedded in epoxy resin so that the cross section could be observed, and polished to a mirror finish using a Maruto ML150-P.

[0047] Figure 8 shows photographs of unidirectionally oriented bamboo fibers (a) and unaligned bamboo fibers that have simply been smoothed (b) coated with 10% FCNF. The white parts in the photo are bamboo fibers. The unidirectionally oriented bamboo fibers (a) are carefully arranged so that the fibers do not cross each other, while the unaligned bamboo fibers (b) that have simply been smoothed out are almost unidirectional, but some of the fibers cross.

[0048] Figures 8 (c) and (d) are micrographs of the cross sections of the bamboo fibers coated with 10% FCNF in Figures 8 (a) and (b), respectively, after hot press molding. In Figure 8(c), the bamboo fibers appear to be clearly deformed horizontally, i.e., perpendicular to the compression direction. On the other hand, in Figure 8(d), the bamboo fibers seem to retain their original shape, resulting in wider gaps between the fibers. This difference in the spacing between the fibers is believed to be the result of the deformation of the fibers being restricted by the intersection of the fibers themselves.

[0049] It is believed that if the deformation of the fibers is insufficient, the contact area between the fibers and the binder will be insufficient, resulting in gaps and preventing efficient stress transmission in the fiber-reinforced composite material. We believe this is the reason why the composite with unidirectionally oriented fibers exhibited mechanical properties that were approximately twice as high as those of the composite with misaligned fibers that had simply been smoothed. In particular, in the case of composites with a high proportion of natural fibers, we believe that the contact area, which depends on the gaps between the fibers, and fiber deformation can be an important factor.

[0050] Figure 9 shows the relationship between hot pressing temperature and flexural modulus and strength for the laminates of 10% FCNF bamboo fiber composites. The hot press temperature was set to seven levels ranging from 150°C to 270°C. Both the flexural modulus and strength are highest at 270°C, a temperature at which typical fiber composite materials are known to char and turn black, and other mechanical properties, such as brittleness, deteriorate.

[0051] In particular, some of the hydrocarbons remaining in the fibres interact with water, pectin, hemicellulose and amorphous cellulose, even at a set temperature of 250°C. Therefore, 230°C was set as the optimal hot pressing temperature. At temperatures above 250°C, the flexural modulus and strength clearly decreased. This is believed to be due to thermal decomposition of the natural fibers.

[0052] Figure 10 is a graph showing the relationship between the bending modulus and the mixed weight ratio of FCNF in a unidirectionally oriented bamboo fiber composite, and Figure 11 is a graph showing the strength of a unidirectionally oriented bamboo fiber composite when the mixed weight ratio of FCNF is changed. The mechanical properties of unidirectionally oriented bamboo fiber composites were a flexural modulus of 28,000-33,000 MPa and a flexural strength of 300-340 MPa when the mixed weight ratio of FCNF to bamboo fiber was 2.5-10.0%, indicating that the composite had greater mechanical properties than misaligned bamboo fiber composites with the same mixed weight ratio. In addition, when the mixed weight ratio of FCNF to bamboo fiber in a unidirectionally oriented bamboo fiber composite was 1.25%, which is less than 2.5%, the flexural modulus was 19,000 MPa and the flexural strength was 280 MPa, which was lower than the mixed weight ratios of 2.5 to 10.0%. It is believed that when the mixed weight ratio of FCNF is low, it is unable to adequately fill the gaps between the bamboo fibers and adhere them together.

[0053] In addition, Table 1 shows the results of measurements of the mechanical strength of bamboo fiber composites with different bamboo fiber orientations when the mixed weight ratio of FCNF was 10% and 5%. In the case of unidirectionally oriented bamboo fiber composites, there was no significant difference in both the flexural modulus and flexural strength when the mixed weight ratio of FCNF was 10% and 5%. However, in the case of non-aligned bamboo fiber composites that were simply smoothed, there was a large difference in both the flexural modulus and flexural strength when the mixed weight ratio of FCNF was 5% compared to when it was 10%. This difference was observed because the gaps between the bamboo fibers in the unidirectionally oriented bamboo fiber composite are smaller than in the non-aligned bamboo fiber composite that has simply been smoothed out, and therefore less FCNF is needed to bond the bamboo fibers together.

[0054] [Table 1]

[0055] From the above results, among the bamboo fiber composites made using the three types of binders, FCNF, CNF, and CBF, the FCNF bamboo fiber composite showed the highest flexural strength and flexural modulus. This is believed to be due to the strong interfacial adhesion between the binder and the fibers, and also because the FCNFs with epoxy groups are chemically activated and bonded to each other.

[0056] In addition, the flexural modulus and strength of the bamboo fiber composite in which the bamboo fibers were oriented in one direction were approximately twice as high as those of the bamboo fiber composite in which the fibers were simply smoothed out but not aligned. It was found that in unidirectionally oriented bamboo fiber composites, the bamboo fibers deform dramatically without any crossing of the fibers. As the fibers deform, the gaps between the fibers narrow, resulting in a high flexural modulus and strength.

[0057] Furthermore, there was a significant variation in the flexural modulus and strength of the bamboo fiber composites when the hot pressing temperatures were different. This indicates that the epoxy groups of FCNF have a suitable temperature for chemical reactions. However, at temperatures above 250°C, thermal decomposition of the natural fibers occurs, decreasing the flexural modulus and strength, so it is necessary to press at temperatures below this level.

Claims

1. A bamboo fiber composite material characterized in that unidirectionally oriented bamboo fibers coated with fluorene-modified cellulose nanofibers in which cellulose is bonded to a fluorene compound having at least one reactive group selected from a carboxyl group or an epoxy group and an aryl group at the 9,9-position, is subjected to heat press molding.

2. A bamboo fiber composite material is characterized in that unidirectionally oriented bamboo fibers coated with fluorene-modified cellulose nanofibers in which cellulose is bonded to a fluorene compound represented by "Chemical Formula 1" (1), which has at least one reactive group selected from a carboxyl group or an epoxy group and an aryl group at the 9,9-position, are heat-press molded. 【Chemistry 1】 [In the formula 1 (1), ring Z is an arene ring, and X is the formula 2 (2-1) or (2-2)] 【Chemistry 2】 (R １ is a hydrogen atom or an alkyl group, R ２ m1 represents an alkylene group, m1 represents an integer of 0 or 1 or more, and m2 represents an integer of 0 or 1 or more; n is an integer from 1 to 3; R ３ and R ４ represents a substituent, p represents an integer of 0 or 1 or more, and k represents an integer of 0 to 4.

3. In the formula (1), ring Z is a monocyclic arene ring, a polycyclic arene ring, or a ring assembly arene ring; １ is a hydrogen atom or C １－４ Alkyl group, R ２ C ２－６ Alkylene group, R ３ C １－４ Alkyl group, C １－４ Alkoxy group, R ４ is a cyano group, a halogen atom, C １－４ Alkyl group, carboxyl group or C １－４ The bamboo fiber composite material according to claim 2, characterized in that it is a fluorene-modified cellulose nanofiber having an alkoxy-carbonyl group, m1 is 0 or an integer of 1 to 4, m2 is 0 or an integer of 1 to 5, n is 1 or 2, p is an integer of 0 to 2, and k is an integer of 0 to 2.

4. In the formula (1), ring Z is a benzene ring, a naphthalene ring, or a biphenyl ring, and X is a group represented by the formula (2-2), R ２ C ２－４ Alkylene group, R ３ C １－３ Alkyl group, R ４ C １－３ Alkyl group, carboxyl group or C １－２ The bamboo fiber composite material according to claim 2 or 3, characterized in that it is a fluorene-modified cellulose nanofiber having an alkoxy-carbonyl group, m2 being 0 or 1, n being 1 or 2, p being an integer of 0 to 2, and k being 0 or 1.

5. A bamboo fiber composite material as described in any one of claims 1 to 4, characterized in that the weight ratio of the fluorene-modified cellulose nanofiber described in any one of claims 1 to 4 with which the bamboo fiber is coated is 2.5 to 10% of the bamboo fiber.

6. A bamboo fiber composite material described in any one of claims 1 to 5, characterized in that the weight ratio of the fluorene-modified cellulose nanofiber described in any one of claims 1 to 5 used to coat the bamboo fiber is 2.5 to 10% of the bamboo fiber, and the bamboo fiber composite material is hot-press molded at 180 to 250 degrees.

7. A bamboo fiber composite material described in any one of claims 1 to 6, characterized in that the weight ratio of the fluorene-modified cellulose nanofiber described in any one of claims 1 to 6 used to coat the bamboo fiber is 2.5 to 10% of the alkali-treated bamboo fiber, and the bamboo fiber composite material is hot-press molded at 180 to 250 degrees.

8. A method for producing a bamboo fiber composite material, characterized in that unidirectionally oriented bamboo fibers are coated with fluorene-modified cellulose nanofibers in which cellulose is bonded to a fluorene compound having at least one reactive group selected from a carboxyl group or an epoxy group and an aryl group at the 9,9-position, and the resulting material is hot-press molded.

9. A method for producing a bamboo fiber composite material, characterized in that unidirectionally oriented bamboo fibers are coated with fluorene-modified cellulose nanofibers in which cellulose is bonded to a fluorene compound represented by "Chemical Formula 3" (1), which has at least one reactive group selected from a carboxyl group or an epoxy group and an aryl group at the 9,9-position, and the resulting material is hot-press molded. 【Chemistry 3】 [In the formula 3 (1), ring Z is an arene ring, and X is the formula 4 (2-1) or (2-2)] 【Chemistry 4】 (R １ is a hydrogen atom or an alkyl group, R ２ m1 represents an alkylene group, m1 represents an integer of 0 or 1 or more, and m2 represents an integer of 0 or 1 or more; n is an integer from 1 to 3; R ３ and R ４ represents a substituent, p represents an integer of 0 or 1 or more, and k represents an integer of 0 to 4.

10. In the formula (1), ring Z is a monocyclic arene ring, a polycyclic arene ring, or a ring assembly arene ring; １ is a hydrogen atom or C １－４ Alkyl group, R ２ C ２－６ Alkylene group, R ３ C １－４ Alkyl group, C １－４ Alkoxy group, R ４ is a cyano group, a halogen atom, C １－４ Alkyl group, carboxyl group or C １－４ The method for producing a bamboo fiber composite material according to claim 9, characterized in that the fluorene-modified cellulose nanofiber is an alkoxy-carbonyl group, m1 is 0 or an integer of 1 to 4, m2 is 0 or an integer of 1 to 5, n is 1 or 2, p is an integer of 0 to 2, and k is an integer of 0 to 2.

11. In the formula (1), ring Z is a benzene ring, a naphthalene ring, or a biphenyl ring, and X is a group represented by the formula (2-2), R ２ C ２－４ Alkylene group, R ３ C １－３ Alkyl group, R ４ C １－３ Alkyl group, carboxyl group or C １－２ The method for producing a bamboo fiber composite material according to claim 9 or 10, characterized in that the fluorene-modified cellulose nanofiber has an alkoxy-carbonyl group, m2 is 0 or 1, n is 1 or 2, p is an integer of 0 to 2, and k is 0 or 1.

12. A method for producing a bamboo fiber composite material described in any one of claims 8 to 11, characterized in that the bamboo fiber composite material is obtained by coating unidirectionally oriented bamboo fibers with fluorene-modified cellulose nanofiber described in any one of claims 8 to 11 in a weight ratio of 2.5 to 10% relative to the bamboo fibers, and then hot press molding the bamboo fiber composite material.

13. A method for producing a bamboo fiber composite material described in any one of claims 8 to 12, characterized in that the bamboo fiber is coated with fluorene-modified cellulose nanofiber described in any one of claims 8 to 12 in a weight ratio of 2.5 to 10% relative to the bamboo fiber, and then hot-press molded at 180 to 250 degrees.

14. A method for producing a bamboo fiber composite material described in any one of claims 8 to 13, characterized in that the bamboo fiber is alkaline-treated with an aqueous sodium hydroxide solution, oriented in one direction, coated with fluorene-modified cellulose nanofiber described in any one of claims 8 to 13 in a weight ratio of 2.5 to 10% relative to the bamboo fiber, and hot-press molded at 180 to 250 degrees.

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