Fiber-reinforced composite material and method for manufacturing the same

Abstract

To provide a fiber-reinforced composite material that is tough during use and easily chemically decomposed. [Solution] A fiber-reinforced composite material comprising reinforcing fibers, a polyrotaxane having a cyclic molecule modified by a graft chain having a first reactive functional group, and a vitrimer having a second reactive functional group capable of undergoing a bond exchange reaction with the first reactive functional group of the cyclic molecule of the polyrotaxane, wherein the total content of the reinforcing fibers, the polyrotaxane, and the vitrimer is 1 to 70 parts by mass of reinforcing fibers, 1 to 20 parts by mass of polyrotaxane, and 10 to 98 parts by mass of vitrimer, with a mass ratio of polyrotaxane to vitrimer of 1 to 40:60 to 99.

Description

[Technical Field]

[0001] This disclosure relates to fiber-reinforced composite materials and methods for manufacturing the same. [Background technology]

[0002] Fiber-reinforced composite materials, which include reinforcing fibers and matrix resins, are used in a wide range of industrial fields such as office equipment, information equipment, and automotive parts, and demand for them is increasing year by year. As matrix resins become more tough and stronger, the interlaminar toughness of fiber-reinforced composite materials can be further enhanced, and it is known that applying polyrotaxane to the resin component of fiber-reinforced composite materials improves their toughness. Patent Document 1 describes the development of a sizing agent containing polyrotaxane and discloses sizing agent-coated reinforced fibers, which are reinforced fibers coated with the sizing agent containing polyrotaxane.

[0003] On the other hand, vitrimers are a new type of material developed in the early 2010s by Dr. Lutwik Leibler et al. in France, which have a covalent network that can change its topology through a heat-activated bond exchange reaction. Patent document 2 discloses a composition containing a vitrimer comprising a polymer having ester bonds, and a polyrotaxane comprising a plurality of cyclic molecules and a chain-like polymer penetrating the openings of the plurality of cyclic molecules, wherein at least a portion of the plurality of cyclic molecules have functional groups having ester bonds. This composition combines toughness and self-healing properties. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6179591 [Patent Document 2] WO2023 / 219145 [Overview of the project] [Problems that the invention aims to solve]

[0005] While there is a demand for resource recycling to reduce environmental impact, thermosetting resins such as epoxy resins commonly used in fiber-reinforced composite materials are not chemically decomposable. They can be decomposed by various methods such as thermal decomposition, liquefaction, or ionization oxidation, but these methods involve harsh conditions that can damage the composite fibers separated from the resin, resulting in surface defects or shortening of the fibers. Damaged fibers tend to have lower physical properties than composite materials made with virgin fibers, so they are cut and used as fiber fillers, which are then downcycled into composite materials.

[0006] While chemical decomposition using various low-molecular-weight solvents such as alcohol and water has been reported for composite fibers using conventional vitrimer resins, the brittle nature of the vitrimer resin results in insufficient fracture toughness, which is problematic for applications in aircraft and next-generation automobiles.

[0007] One of the problems that this disclosure aims to solve is to provide a fiber-reinforced composite material that achieves both toughness during use and ease of chemical decomposition, as well as a method for manufacturing the same. [Means for solving the problem]

[0008] This disclosure includes, for example, the following subjects:

[0009] Section 1. A fiber-reinforced composite material comprising reinforcing fibers, a polyrotaxane having a cyclic molecule modified by a graft chain having a first reactive functional group, and a vitrimer having a second reactive functional group capable of undergoing a bond exchange reaction with the first reactive functional group of the cyclic molecule of the polyrotaxane, A fiber-reinforced composite material comprising 1 to 70 parts by mass of reinforcing fibers, 1 to 20 parts by mass of polyrotaxane, and 10 to 98 parts by mass of vitrimer, with a total content of 100 parts by mass of the reinforcing fibers, the polyrotaxane, and the vitrimer, wherein the mass ratio of polyrotaxane to vitrimer is 1 to 40:60 to 99. Section 2. The fiber reinforced composite material according to item 1, which is a reinforcing fiber coated with a composition containing polyrotaxane and vitrimer. Item 3. The fiber reinforced composite material according to item 1, wherein the mass ratio of polyrotaxane to vitrimer is 10 to 40:70 to 90. Item 4. The value of G measured according to JIS K7086 IC and the value of G measured according to JIS K7086 IIC satisfy that G IIC - G IC is 2 or more, and G IC + G IIC is 4 or more. The fiber reinforced composite material according to item 1. Item 5. The fiber reinforced composite material according to any one of items 1 to 4, wherein the reinforcing fiber contains carbon fiber or glass fiber. Item 6. The fiber reinforced composite material according to any one of items 1 to 4, wherein the vitrimer contains a thermosetting resin. Item 7. A method for manufacturing a fiber reinforced composite material, comprising: applying a composition containing polyrotaxane and vitrimer to a reinforcing fiber, and heating the reinforcing fiber coated with the composition A method including. Item 8. A method for recycling a fiber reinforced composite material, comprising: heating the fiber reinforced composite material according to any one of items 1 to 4 in a solvent at 200 ° C or lower, and making the rate of the vitrimer remaining on the reinforcing fiber 50% or less within 24 hours from the start of heating. A method including.

Advantages of the Invention

[0010] According to the present disclosure, it is possible to provide a fiber reinforced composite material that exhibits toughness during use and can be easily chemically decomposed after use. A method for manufacturing such a fiber reinforced composite material can also be provided. [[ID=I53]]

Brief Description of the Drawings

[0011] [Figure 1A]Schematic diagram of the DCB test method. [Figure 1B] A graph showing the relationship between polyrotaxane content and fracture toughness (GIC). [Figure 2A] Schematic diagram of the ENF test method. [Figure 2B] A graph showing the relationship between polyrotaxane content and fracture toughness (GIIC). [Figure 3A] Graphs of fracture toughness (GIC) for each sample containing the same carbon fiber. A: Carbon fiber only, B: Composite material of carbon fiber and polyrotaxane, C: Composite material of carbon fiber and vitrimer, X1, X2: Composite material of carbon fiber, vitrimer, and polyrotaxane [Figure 3B] Graphs of fracture toughness GIIC for each sample with the same carbon fiber. A: Carbon fiber only, B: Composite material of carbon fiber and polyrotaxane, C: Composite material of carbon fiber and vitrimer, X1, X2: Composite material of carbon fiber, vitrimer, and polyrotaxane [Figure 3C] A graph showing the relationship between fracture toughness GIC and fracture toughness GIIC for each sample. [Figure 3D] A graph showing the relationship between GIIC-GIC and GIC+GIIC for each sample. [Figure 4A] A graph showing the relationship between fracture toughness GIC and fracture toughness GIIC for carbon fiber reinforced plastics (multiple points enclosed by dashed lines), composite materials of carbon fiber and vitrimer (point C), and composite materials of carbon fiber, vitrimer, and polyrotaxane (points X1, X2). [Figure 4B] A graph showing the relationship between GIIC-GIC and GIC+GIIC for carbon fiber reinforced plastics (multiple points enclosed by dashed lines), composite materials of carbon fiber and vitrimer (point C), and composite materials of carbon fiber, vitrimer, and polyrotaxane (points X1, X2). [Figure 5] Photographs of a composite material of carbon fiber, vitrimer, and polyrotaxane (left) and the composite material after decomposition by heating in a solvent (right). [Figure 6] A graph showing the resin retention rate over time in composite materials. [Figure 7]Electron microscope images of untreated carbon fibers (left), carbon fibers recovered from a composite material of carbon fibers and vitrimer (center), and carbon fibers recovered from a composite material of carbon fibers, vitrimer, and polyrotaxane (right). [Modes for carrying out the invention]

[0012] In this specification, the singular form includes both singular and plural forms unless otherwise explicitly stated herein or the context clearly contradicts it.

[0013] In this specification, "contains" is a concept that also includes "substantially consists only of" and "consists only of."

[0014] In the numerical ranges described stepwise in this specification, the upper or lower limit of a numerical range in one step can be arbitrarily combined with the upper or lower limit of a numerical range in another step. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of a numerical range may be replaced with values ​​shown in the examples or values ​​that can be uniquely derived from the examples. Moreover, in this specification, numbers connected by "~" mean a numerical range that includes the numbers before and after "~" as the lower and upper limits.

[0015] In this specification, "epoxy resin" refers to a thermosetting resin obtained by reacting a prepolymer having two or more epoxy groups in its molecule with a curing agent. In this specification, "thermoplastic resin" refers to a resin that softens when it reaches its glass transition temperature or melting point. In this specification, "chemical decomposition" refers to the property of being broken down by chemical substances.

[0016] The embodiments included in this disclosure will be described further below. The embodiments described below are examples of typical embodiments of this disclosure and do not limit the scope of the invention.

[0017] This disclosure provides a fiber-reinforced composite material comprising reinforcing fibers, a polyrotaxane having a cyclic molecule modified by a graft chain having a first reactive functional group, and a vitrimer having a second reactive functional group capable of undergoing a bond exchange reaction with the first reactive functional group of the cyclic molecule of the polyrotaxane, wherein the total content of the reinforcing fibers, polyrotaxane, and vitrimer is 1 to 70 parts by mass of reinforcing fibers, 1 to 20 parts by mass of polyrotaxane, and 10 to 98 parts by mass of vitrimer, with a mass ratio of polyrotaxane to vitrimer (polyrotaxane:vitrimer) of 1 to 40:60 to 99. Hereinafter, "polyrotaxanes having a cyclic molecule modified by a graft chain having a first reactive functional group" may be simply referred to as "polyrotaxanes," and "vitrimers having a second reactive functional group capable of undergoing a bond exchange reaction with the first reactive functional group of the cyclic molecule of a polyrotaxane" may be simply referred to as "vitrimers."

[0018] Examples of reinforcing fibers include, but are not limited to, various inorganic fibers such as carbon fibers, glass fibers, ceramic fibers, and silicon carbide fibers; and various organic fibers such as aromatic polyamide fibers (aramid fibers), polyethylene fibers, polyethylene terephthalate fibers, polybutylene terephthalate fibers, polyethylene naphthalate fibers, polyarylate fibers, polyacetal fibers, poly(p-phenylene benzoxazole) fibers, polyphenylene sulfide fibers, and polyketone fibers. The reinforcing fibers preferably include inorganic fibers such as carbon fibers and glass fibers, or aromatic polyamide fibers, more preferably carbon fibers or glass fibers, and even more preferably carbon fibers.

[0019] Polyrotaxanes are compounds having a structure in which a chain-like polymer penetrates the opening of a cyclic molecule, and sealing groups are bonded to both ends of the chain-like polymer to prevent the cyclic molecule from falling off. Polyrotaxanes may be manufactured based on known literature, or commercially available products from manufacturers such as ASM Inc. may be used.

[0020] Examples of cyclic molecules constituting polyrotaxanes include various cyclodextrins (α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and their derivatives, preferably derivatives that retain the carbon skeleton of cyclodextrin and in which any one or more functional groups attached to the carbon skeleton are substituted), crown ethers, benzocrowns, dibenzocrowns, dicyclohexanocrowns, and their derivatives.

[0021] As the cyclic molecule, a cyclic molecule having a hydroxyl group is preferred, and cyclodextrin is more preferred from the viewpoint of inclusion and productivity. Here, cyclodextrin derivatives may also be used as cyclodextrin. The type of cyclodextrin or cyclodextrin derivative is not particularly limited, but those selected from α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and their derivatives are preferred. Here, a cyclodextrin derivative is one in which a polymer chain and / or substituents are introduced by substituting them for the hydroxyl group of cyclodextrin. By appropriately selecting these polymer chains and / or substituents, the dispersibility of the polyrotaxane can be adjusted. Examples of such polymer chains include polyethylene glycol, polypropylene glycol, polyethylene, polypropylene, polyvinyl alcohol, polyacrylic acid esters, polylactones, and polylactams. On the other hand, examples of the substituents include alkyl groups such as hydroxyl groups, thionyl groups, amino groups, sulfonyl groups, phosphonyl groups, acetyl groups, methyl groups, ethyl groups, propyl groups, and isopropyl groups, as well as trityl groups, tosyl groups, trimethylsilane groups, and phenyl groups. By introducing polymer chains or substituents, the affinity between the polyrotaxane and the vitrimer is increased, good dispersibility of the polyrotaxane is provided, and strong adhesion between the vitrimer and the reinforcing fiber surface can be achieved.

[0022] From this viewpoint, it is even more preferable that the cyclodextrin is modified by a polymer chain. The polymer chain preferably contains bonds selected from -O- bonds and -NH- bonds, and groups selected from alkylene groups and alkenylene groups. Here, the alkylene group preferably has 1 to 20 carbon atoms, and more preferably has 2 to 12 carbon atoms. The alkenylene group preferably has 2 to 20 carbon atoms, and more preferably has 2 to 12 carbon atoms. When the cyclic molecule is a cyclodextrin, since the cyclodextrin has a hydroxyl group in its molecule, an ester bond can be introduced into the cyclic molecule by reacting the cyclodextrin with an acid. Examples of such polymer chains include polyalkylene glycol, polyalkenylene glycol, polyalkyleneimine, polylactone, and polylactam. Preferred specific examples include polyethylene glycol, polypropylene glycol, polyethyleneimine, polyβ-propiolactone, polyδ-valerolactone, polyε-caprolactone, polyε-caprolactam, and polylauryllactam. Furthermore, some of the hydrogen atoms of the alkylene or alkenylene group may be substituted with at least one selected from the group consisting of hydroxyl groups, carboxyl groups, acyl groups such as acetyl groups, phenyl groups, halogen atoms, and olefin groups such as allyl groups.

[0023] Examples of chain polymers constituting polyrotaxanes include molecules that can penetrate the rings of multiple cyclic molecules. Preferably, the chain polymer is a polymer having repeating units of monomers. Examples of chain polymers include long-chain fatty acids with 12 or more carbon atoms, polyvinyl alcohol, polyvinylpyrrolidone, poly(meth)acrylic acid, cellulosic resins (carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, etc.), polyacrylamide, polyethylene oxide, polyethylene glycol, polypropylene glycol, polyvinyl acetal resins, polyvinyl methyl ether, polyamine, polyethyleneimine, casein, gelatin, starch, etc. and / or copolymers thereof, polyethylene, polypropylene, and other olefin monomer copolymer resins such as polyolefin resins, polyester resins, polyvinyl chloride resins, polystyrene resins such as polystyrene and acrylonitrile-styrene copolymer resins, polymethyl methacrylate, and Examples of polymers include acrylic resins such as (meth)acrylic acid ester copolymers and acrylonitrile-methyl acrylate copolymer resins, polycarbonate resins, polyurethane resins, vinyl chloride-vinyl acetate copolymer resins, polyvinyl butyral resins, etc., and their derivatives or modified forms, polyisobutylene, polytetrahydrofuran, polyaniline, acrylonitrile-butadiene-styrene copolymer (ABS resin), polyamides such as nylon, polyimides, polyisoprene, polydienes such as polybutadiene, polysiloxanes such as polydimethylsiloxane, polysulfones, polyimines, polyacetic anhydride, polyureas, polysulfides, polyphosphazenes, polyketones, polyphenylenes, polyhaloolefins, and derivatives thereof. For example, it is preferable to select from the group consisting of polyethylene glycol, polyisoprene, polyisobutylene, polybutadiene, polypropylene glycol, polytetrahydrofuran, polydimethylsiloxane, polyethylene, polypropylene, polyvinyl alcohol, and polyvinyl methyl ether. Polyethylene glycol and polypropylene glycol are particularly preferable.

[0024] The molecular weight of the chain polymer is not particularly limited, but is more preferably, by number average molecular weight, for example, 3,000 to 500,000, more preferably 7,000 to 200,000, and even more preferably 10,000 to 100,000. Alternatively, by weight average molecular weight, for example, is more preferably 3,000 to 500,000, more preferably 7,000 to 200,000, and even more preferably 10,000 to 100,000. The number average molecular weight and weight average molecular weight as used herein can be determined from polyethylene glycol equivalent values ​​obtained by gel permeation chromatography (GPC) measurement.

[0025] The chelating group bonded to the chain polymer of the polyrotaxane is not particularly limited as long as it is a group that acts to prevent the detachment of the cyclic molecule from the chain polymer. For example, the chelating group is preferably selected from the group consisting of dinitrophenyl, cyclodextrin, adamantane, trityl, fluorescein, silsesquioxane, pyrene, substituted benzene (substituents include, but are not limited to, alkyl, alkyloxy, hydroxy, halogen, cyano, sulfonyl, carboxyl, amino, and phenyl; there may be one or more substituents), substituted polynuclear aromatic (substituents include, but are not limited to, the same as above; there may be one or more substituents), and steroids. Preferably, the chelating group is selected from the group consisting of dinitrophenyl, cyclodextrin, adamantane, trityl, fluorescein, silsesquioxane, and pyrene, with adamantane or cyclodextrin being more preferred.

[0026] Multiple polyrotaxanes may be crosslinked with each other via the functional groups of cyclic molecules. The functional groups of the cyclic molecules of the multiple polyrotaxanes may be directly bonded to each other, or they may be bonded via a crosslinking agent that is reactive with the functional groups of the cyclic molecules. Elastomerization of the polyrotaxanes by crosslinking can make the composition containing the vitrimer containing the polymer having ester bonds of this embodiment and the polyrotaxanes even tougher.

[0027] In this specification, inclusion rate refers to the ratio of the amount of cyclic molecules inclusion of a chain polymer to the maximum amount of cyclic molecules inclusion of the chain polymer. The inclusion rate can be determined, for example, by nuclear magnetic resonance spectroscopy (NMR) or gel permeation chromatography (GPC).

[0028] The inclusion rate of polyrotaxane is preferably 0.1 to 100%, more preferably 0.1 to 50%, even more preferably 1 to 50%, and most preferably 1 to 30%.

[0029] The vitrimer having the second reactive functional group may contain a thermosetting resin or a thermoplastic resin. It is preferable to include a thermosetting resin in order to promote the recycling of fiber-reinforced composite materials.

[0030] Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, melamine resins, urea resins, thermosetting polyimide resins, cyanate ester resins, and bismaleimide resins, as well as modified versions thereof, and resins obtained by blending two or more of these. Epoxy resins are preferred. In certain embodiments, the epoxy resin includes glycidyl-type epoxy resins.

[0031] Glycidyl-type epoxy resins are obtained by reacting an epoxy prepolymer having glycidyl groups with a curing agent.

[0032] In some embodiments, the epoxy prepolymer having a glycidyl group is a compound represented by the following formula (I).

[0033] [ka] (In the formula, X is O, NH, or C(O)O, R is a divalent aliphatic and / or aromatic moiety, and n is the degree of polymerization, where n is between 0 and 25.)

[0034] In some embodiments, in formula (I), X is O, R is a divalent aliphatic and / or aromatic moiety, and n is between 0 and 5.

[0035] Those skilled in the art will understand epoxy prepolymers having glycidyl groups suitable for embodiments of the present invention. Examples of such epoxy prepolymers having glycidyl groups include bisphenol A glycidyl ether (DGEBA), bisphenol F diglycidyl ether, trimethylol triglycidyl ether (TMPTGE), ethylene glycol glycidyl ether, bisphenol A polyethylene glycol diglycidyl ether, bisphenol A polypropylene glycol diglycidyl ether, epoxidized polyunsaturated fatty acids, epoxidized alicyclic compounds, and combinations thereof. In one preferred embodiment, the epoxy prepolymer having glycidyl groups is bisphenol A glycidyl ether (DGEBA).

[0036] The curing agent is preferably a curing agent having multiple functional groups, such as anhydrides, acids, or hydroxyl groups, in a single molecule that can react with the reactive groups of the epoxy prepolymer having glycidyl groups to form ester bonds. In preferred embodiments, the curing agent is a carboxylic acid or a carboxylic acid anhydride. Examples of carboxylic acids include, but are not limited to, glutaric acid and sebacic acid. Examples of carboxylic acid anhydrides include, but are not limited to, glutaric acid anhydride, succinic acid anhydride, tetrahydrophthalic acid anhydride (THPA), and hexahydrophthalic acid anhydride (HMPA).

[0037] In some embodiments, the epoxy prepolymer having a glycidyl group is an epoxy prepolymer having a glycidyl group, the curing agent is a carboxylic acid or carboxylic acid anhydride, and the epoxy resin is a reaction product thereof.

[0038] In some embodiments, thermosetting resins are cured without the use of a curing agent. For example, among thermosetting resins, those having benzoxazine, maleimide, nadiimide, or ethynyl groups as terminal thermal crosslinking groups at both ends of the polymer chain are self-thermally crosslinkable and therefore do not require a curing agent. Alternatively, epoxy resins having aromatic acetal groups and epoxy groups in a single molecule can also self-cure. Such self-curing thermosetting properties of resins are readily understood by those skilled in the art.

[0039] The molecular weight of the thermosetting resin constituting the vitrimer having the second reactive functional group is not particularly limited and may be, for example, 500 to 2,000,000 in number average molecular weight or weight average molecular weight, and may be a low molecular weight of less than 10,000 or a high molecular weight of 10,000 or more.

[0040] In some embodiments, the vitrimer having a second reactive functional group includes a thermoplastic resin. Examples in specific embodiments include polyester resins, polyurethane resins, or combinations thereof. Examples of thermoplastic resins include those having bonds selected from the group consisting of carbon-carbon bonds, amide bonds, imide bonds (such as polyetherimide), ester bonds, ether bonds, siloxane bonds, carbonate bonds, urethane bonds, urea bonds, thioether bonds, sulfone bonds, imidazole bonds, and carbonyl bonds in the main chain. For example, materials that combine heat resistance and toughness, such as polysulfone, polyethersulfone, polyetherimide, polyimide, polyamide, polyamideimide, polyphenylene ether, phenoxy resin, and vinyl polymers, can be preferably used.

[0041] Examples of polyester resins include aliphatic polyesters, alicyclic polyesters, aromatic polyesters, and aliphatic aromatic polyesters.

[0042] Polyester resins can be prepared by condensation polymerization reactions of polycarboxylic acids (including dicarboxylic acids and tricarboxylic acids) and polyols (including diols and triols), condensation polymerization reactions of hydroxycarboxylic acids, condensation polymerization reactions of polycarboxylic acids (including dicarboxylic acids and tricarboxylic acids), polyols (including diols and triols), and hydroxycarboxylic acids, and condensation polymerization reactions of acid anhydrides and polyols (including diols and triols). The polycarboxylic acid (including dicarboxylic acids and tricarboxylic acids) is preferably a saturated polycarboxylic acid. Polyester vitrimers can be produced by reacting these monomers, preferably under a transesterification catalyst as described later.

[0043] The hydrocarbon chain portion of the polyester may be unsubstituted, but it may also contain functional groups such as ether groups, carbonyl groups, or ester groups within the hydrocarbon chain.

[0044] Aliphatic polyesters include polycaprolactone (PCL), polypivalolactone, polylactic acid (PLA), polyglycolic acid (PGA), polyhydroxyalkanoic acid (PHA), copolymers thereof, or combinations thereof. Copolymers include polyhydroxyalkanoates (PHA) such as poly(3-hydroxybutyrate-co-hydroxyhexanoate) (3HB-co-3HH) and poly(3-hydroxybutyrate-co-3-hydroxyvalate) (3HB-co-3HV), polylactic acid-co-polyglycolic acid (PLGA), polylactic acid-co-polycaprolactone, polyethylene succinate (PES), polybutylene succinate (PBS), and polybutylene succinate adipate (PBSA).

[0045] Examples of alicyclic polyesters include polyethylenecyclohexanoate and other polyC2-6 alkylene C6-12 cycloalkanoates.

[0046] Examples of aromatic polyesters include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polytrimethylene naphthalate, polytetramethylene naphthalate, etc., which are C 2-6 polyalkylene C 6-12 arylate (homopolyester), C 2-6 polyalkylene C 6-12 copolymers containing arylate units (e.g., C 2-6 polyalkylene C 6-12 copolyesters obtained by copolymerizing polyalkylene arylate with aromatic dicarboxylic acids such as adipic acid, isophthalic acid, and phthalic acid), etc.

[0047] Examples of aliphatic aromatic polyesters include polybutylene adipate-co-terephthalate (PBAT), polytetramethylene adipate-co-terephthalate, polyethylene terephthalate succinate (PETS), etc.

[0048] In some embodiments, the vitrimer having a second reactive functional group may be a vitrimer having an ester bond described in the known literature. Examples include the vitrimers described in M. Capelot et al., J. Am. Chem. Soc., 2012, 134, 7664 - 7667, Y. Yang et al., Chem. Sci., 2014, 5, 3486 - 3492, J. P. Brutman et al., ACS Macro Lett., 2014, 3, 607 - 610, etc.

[0049] The molecular weight of the thermoplastic resin constituting the vitrimer having a second reactive functional group is not particularly limited. For example, in terms of number average molecular weight or weight average molecular weight, it may be 500 - 2000000, and may be a low molecular weight of less than 10000 or a high molecular weight of 10000 or more.

[0050] In the present invention, the polyrotaxane has a plurality of cyclic molecules, and some or all of the plurality of cyclic molecules are modified by a graft chain having a first reactive functional group. All cyclic molecules in the polyrotaxane in the fiber-reinforced composite material may have the first reactive functional group, but it is sufficient that at least some of the cyclic molecules in the polyrotaxane in the reinforced fiber composite material have the first reactive functional group, as long as a bond exchange reaction occurs between the second reactive functional group of the vitrimer and the first reactive functional group of the cyclic molecules of the polyrotaxane.

[0051] When a fiber-reinforced composite material is subjected to external stimuli such as stress and / or heat, bond exchange occurs between the first reactive functional group of the polyrotaxane and the second reactive functional group of the vitrimer. Preferably, the crosslinking bonds do not disappear during bond exchange, and associative dynamic covalent bonds are formed at the crosslinking bonds.

[0052] The combination of the first reactive functional group of the polyrotaxane cyclic molecule and the second reactive functional group of the vitrimer is not particularly limited as long as it produces a bond exchange reaction, but examples are shown in Table 1. The first and second reactive functional groups may be reversed.

[0053] [Table 1] In the table, R 1 R is an alkyl group, an alkynyl group, an alkenyl group, or a phenyl group. 2 This group is an alkyl group, an alkynyl group, an alkenyl group, or a phenyl group.

[0054] In certain embodiments, combinations of the first reactive functional group of the cyclic molecule of the polyrotaxane and the second reactive functional group of the vitrimer include ester and hydroxyl group, carbamate group and hydroxyl group, carbonate group and hydroxyl group, carbamide and amino group, acetal and hydroxyl group, imine and amino group, vinyl urethane and amino group, diketoneamine and amino group, thioether and thiol group, triazolium with triazolium, pyridinium with pyridinium, anilinium with anilinium, sulfonium with sulfonium, dioxysaborolane and polyol (diol), boroxane and polyol (diol), silyl ether and hydroxyl group, disulfide and thiol group, and the like.

[0055] In addition, the material may be a combination of ester bonds, or it may further have at least one selected from the group consisting of thioester bonds, carbonyl groups, hydroxyl groups, urethane bonds, urea bonds, associated bonds between aldehydes and imines that undergo aldehyde-imine bond exchange reactions, associated bonds between imines that undergo imine-imine bond exchange reactions, associated bonds between amines and imines that undergo amine-imine bond exchange reactions, associated bonds between vinylogue amide or vinylogue urethane and amines that undergo amino exchange reactions, associated bonds between poly(1,2,3-triazolium) ionic liquids (PTILs) and a bifunctional crosslinking agent that undergo transalkylation reactions of CN bonds, addition and elimination of silanol / silanolate at the siloxane moiety, and associated bonds by disulfides that undergo disulfide bond exchange reactions.

[0056] The toughness of a fiber-reinforced composite material containing reinforcing fibers, a polyrotaxane having a cyclic molecule modified by a graft chain having a first reactive functional group, and a vitrimer having a second reactive functional group capable of undergoing a bond exchange reaction with the first reactive functional group of the cyclic molecule of the polyrotaxane, is unexpectedly increased compared to the toughness of fiber-reinforced composite materials without polyrotaxane or without vitrimer. While we do not wish to be bound by theory, in addition to the known effect of toughening the resin by the pulley-like polyrotaxane, it is thought that the polyrotaxane dissipates the forces between the reinforcing fibers and the vitrimer. That is, the interface between the reinforcing fibers and the vitrimer breaks due to stress, but the presence of polyrotaxane at that interface achieves further toughness. It should be noted that even fiber-reinforced composite materials manufactured without fully following the above theory are included within the technical scope of the present invention if they satisfy the requirements specified in the present invention.

[0057] On the other hand, as materials become harder, their bond exchangeability generally decreases, and in fiber-reinforced composite materials consisting of reinforcing fibers and a thermosetting resin such as vitrimer, the decomposition rate decreases. However, adding polyrotaxane to such resins improves both bond exchangeability and decomposition rate. Improved decomposition rate allows for lower heating temperatures required for decomposition, thus saving energy. While thermosetting resin fibers have traditionally been difficult to recycle, the ability to easily decompose or separate the reinforcing fibers and vitrimer at low temperatures is advantageous.

[0058] The fiber-reinforced composite material contains 1 to 70 parts by mass of reinforcing fibers, 1 to 20 parts by mass of polyrotaxane, and 10 to 98 parts by mass of vitrimer per 100 parts by mass of the total amount of reinforcing fibers, polyrotaxane, and vitrimer. When the total amount of polyrotaxane and vitrimer is 100 parts by mass, the proportion of polyrotaxane is 1 to 40 parts by mass and the proportion of vitrimer is 60 to 99 parts by mass.

[0059] When the amount of reinforcing fiber is 1 to 70 parts by mass per 100 parts by mass of the total content of reinforcing fiber, polyrotaxane, and vitrimer, it is preferable in terms of the function of the reinforcing fiber in the fiber-reinforced composite material. When the amount of polyrotaxane is less than 1 part by mass per 100 parts by mass of the total content of reinforcing fiber, polyrotaxane, and vitrimer, the enhancement of toughness may be insufficient. Similarly, when the amount of vitrimer is less than 10 parts by mass per 100 parts by mass of the total content of reinforcing fiber, polyrotaxane, and vitrimer, the enhancement of toughness due to the bond exchange reaction of the vitrimer may also be insufficient. When the total content of reinforcing fiber, polyrotaxane, and vitrimer is 1 to 20 parts by mass of polyrotaxane and 10 to 98 parts by mass of vitrimer, the amount of binder relative to the reinforcing fiber is sufficient, and it is preferable in terms of enhancing the toughness of the fiber-reinforced composite material and the chemical decompositionability of the fiber-reinforced composite material. When the total amount of polyrotaxane and vitrimer is 100 parts by mass, it is preferable that the proportion of polyrotaxane is 1 to 40 parts by mass and the proportion of vitrimer is 60 to 99 parts by mass. This is preferable in terms of enhancing the toughness of the fiber-reinforced composite material and the chemical decomposition properties of the fiber-reinforced composite material.

[0060] In some embodiments, the fiber-reinforced composite material contains 20 to 70 parts by mass of reinforcing fibers, 1 to 20 parts by mass of polyrotaxane, and 10 to 79 parts by mass of vitrimer, with the total content of reinforcing fibers, polyrotaxane, and vitrimer being 100 parts by mass, and the proportion of polyrotaxane being 5 to 40 parts by mass and the proportion of vitrimer being 60 to 95 parts by mass when the total amount of polyrotaxane and vitrimer is 100 parts by mass. In further embodiments, the total content of polyrotaxane and the vitrimer is 100 parts by mass, and the mixture contains 25 to 70 parts by mass of reinforcing fibers, 5 to 20 parts by mass of polyrotaxane, and 25 to 70 parts by mass of vitrimer, and when the total amount of polyrotaxane and vitrimer is 100 parts by mass, the proportion of polyrotaxane is 1 to 20 parts by mass and the proportion of vitrimer is 80 to 99 parts by mass, or the proportion of polyrotaxane is 10 to 20 parts by mass and the proportion of vitrimer is The proportion is 80-90 parts by mass, or the proportion of polyrotaxane is 10-30 parts by mass and the proportion of vitrimer is 70-90 parts by mass, or the proportion of polyrotaxane is 10-40 parts by mass and the proportion of vitrimer is 60-90 parts by mass, or the proportion of polyrotaxane is 20-40 parts by mass and the proportion of vitrimer is 60-80 parts by mass, or the proportion of polyrotaxane is 30-40 parts by mass and the proportion of vitrimer is 60-90 parts by mass. Such a configuration is more preferable in terms of toughening and degradability of the fiber-reinforced composite material.

[0061] In some embodiments, the fiber-reinforced composite material contains 34 to 65 parts by mass of reinforcing fibers, 1 to 13 parts by mass of polyrotaxane, and 35 to 53 parts by mass of vitrimer, per 100 parts by mass of the total content of reinforcing fibers, polyrotaxane, and vitrimer, with a mass ratio of polyrotaxane to vitrimer of 1 to 20:80 to 99. Such a configuration is more preferable in terms of toughening and degradability of the fiber-reinforced composite material.

[0062] When the amount of reinforcing fiber in the above embodiment is 100 parts by mass, the amount of polyrotaxane is not particularly limited, but is preferably 5 to 30 parts by mass, and more preferably 5 to 20 parts by mass. When the amount of reinforcing fiber in the above embodiment is 100 parts by mass, the total amount of the polyrotaxane and the vitrimer is not particularly limited, but is more preferably 45 to 102 parts by mass.

[0063] When the amount of reinforcing fibers in the above fiber-reinforced composite material is 100 parts by mass, the proportion of polyrotaxane and the proportion of vitrimer are not particularly limited, but in terms of toughening and degradability of the fiber-reinforced composite material, it is preferable that the proportion of polyrotaxane is 10 to 20 parts by mass and the proportion of vitrimer is 30 to 40 parts by mass. When the amount of reinforcing fibers is 100 parts by mass, the proportion of polyrotaxane may be 10 to 30 parts by mass and the proportion of vitrimer may be 20 to 40 parts by mass, or the proportion of polyrotaxane may be 5 to 30 parts by mass and the proportion of vitrimer may be 20 to 45 parts by mass, or the proportion of polyrotaxane may be 1 to 30 parts by mass and the proportion of vitrimer may be 20 to 49 parts by mass.

[0064] The proportions of the polyrotaxane and the vitrimer are not particularly limited, but in terms of toughening and degradability of the fiber-reinforced composite material, the mass ratio of the polyrotaxane to vitrimer may be 10-40:60-90, 10-30:70-90, 20-40:60-80, or 30-40:60-70.

[0065] In certain embodiments, the mass ratio of polyrotaxane to vitrimer is 10-20:80-90. With such a configuration, the fracture toughness can be improved by approximately 2.5 times and the chemical decomposition rate by approximately 3 times compared to fiber-reinforced composite materials that do not contain polyrotaxane. This is advantageous because, while the fiber-reinforced composite material is strong and durable in its operating environment, it can be decomposed with low energy (low temperature) and in a short time when decomposition is desired.

[0066] The fiber-reinforced composite material of the present disclosure preferably comprises a catalyst that facilitates a bond exchange reaction between a polyrotaxane having a cyclic molecule modified by a graft chain having a first reactive functional group and a vitrimer having a second reactive functional group.

[0067] In some embodiments, such catalysts include transesterification catalysts. The transesterification catalyst is a catalyst that causes a transesterification reaction within the resulting vitrimer and / or between the vitrimer and the polyrotaxane. Such transesterification catalysts are known and include, but are not limited to, zinc acetate (Zn(OAc)2) and its hydrate, zinc acetylacetonate (Zn(acac)2) and its hydrate, triazabicyclodecene (TBD), tetraisopropyl titanate, antimony trioxide, dibutyltin dioctylate, dibutyltin dilaurate (DBTDL), monobutyltin oxide (MBTO), and dibutyltin oxide (DBTO). The amount of transesterification catalyst added can be appropriately determined by those skilled in the art. The amount of transesterification catalyst is not limited, but is, for example, 0.001 to 10 parts by mass per 100 parts by mass of the vitrimer or the resin constituting the vitrimer.

[0068] The fiber-reinforced composite material of this disclosure may contain other additives in addition to the reinforcing fibers, polyrotaxane, and vitrimer, such as plasticizers, surfactants, lubricants, fillers, dispersants, antioxidants, light stabilizers, UV absorbers, colorants, and flame retardants. These additives can be used individually or in combination of two or more.

[0069] In some embodiments, the fiber-reinforced composite material is a reinforcing fiber coated with the polyrotaxane and the vitrimer.

[0070] In some embodiments, the fiber-reinforced composite material is a reinforcing fiber coated with a resin composition containing the polyrotaxane and the vitrimer. The amounts and ratios of the reinforcing fiber, the polyrotaxane, and the vitrimer also apply to these embodiments.

[0071] The fiber-reinforced composite material of this disclosure has a fracture toughness value in DCB testing that is preferably 2 times or more, and more preferably 2.5 times or more, than that of a fiber-reinforced composite material with the same composition except that it does not contain polyrotaxane. By satisfying these requirements, a fiber-reinforced composite material with excellent toughness is provided.

[0072] The fiber-reinforced composite material of this disclosure has a fracture toughness value in ENF testing that is preferably 1.5 times or more, and more preferably 2 times or more, than that of a fiber-reinforced composite material with the same composition except that it does not contain polyrotaxane. By satisfying these requirements, a fiber-reinforced composite material with excellent toughness is provided.

[0073] The fiber-reinforced composite material of this disclosure preferably has a G measured according to JIS K7086. IC The value is greater than 0.8, or G is measured according to JIS K7086. IIC The value of is greater than 2.5, or both. G IC This represents the delamination strength in the opening mode, G IIC This indicates the interlaminar toughness in the in-plane shear mode. IC and G IIC The measurement method follows the conditions of the examples. By satisfying these requirements, a fiber-reinforced composite material with high delamination strength and excellent toughness is provided.

[0074] The fiber-reinforced composite material of this disclosure preferably has a G measured according to JIS K7086. IC The value and G measured according to JIS K7086 IIC The value of G IIC -G IC If the condition is 2 or more, G IC +G IIC The condition satisfies 4 or more, or both conditions. By satisfying these requirements, a fiber-reinforced composite material with high delamination strength and excellent toughness is provided.

[0075] Next, a method for manufacturing a fiber-reinforced composite material according to an embodiment of this disclosure will be described.

[0076] First, prepare the reinforcing fibers. It is convenient to cut the reinforcing fibers to a size suitable for use. The reinforcing fibers of this disclosure can be used in the form of, for example, tow, woven fabric, knitted fabric, braid, web, mat and chopped fiber.

[0077] The polyrotaxane applied to the reinforcing fibers may be diluted with a solvent, or it may be dissolved in a vitrimer without using a solvent. Furthermore, the polyrotaxane and vitrimer may be applied to the reinforcing fibers at the same time or at different times. However, to ensure uniform dispersion of the polyrotaxane and vitrimer on the reinforcing fibers, it is preferable to apply a composition containing the polyrotaxane and vitrimer to the reinforcing fibers. The application can be done in a single application or in multiple applications. The preferred amounts of polyrotaxane and vitrimer relative to the reinforcing fibers are as described above.

[0078] Examples of solvents include water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, dimethylformamide, and dimethylacetamide. Among these, water is preferred because it is easy to handle and advantageous from a safety standpoint. It is also possible to add a surfactant and use it as an aqueous emulsion. There are no particular limitations on the surfactant, but nonionic surfactants such as block copolymers of ethylene oxide and propylene oxide are preferred.

[0079] Examples of application methods include spraying a composition containing polyrotaxane and vitrimer onto reinforcing fibers, immersing reinforcing fibers in a composition containing polyrotaxane and vitrimer, and bringing reinforcing fibers into contact with a roller to which a composition containing polyrotaxane and vitrimer is attached.

[0080] Further coating methods include the wet method and the hot melt method. The wet method involves immersing the reinforcing fibers in a composition solution containing polyrotaxane and vitrimer, then removing them and evaporating the solvent using a heating device. The hot melt method involves directly impregnating the reinforcing fibers with a composition containing polyrotaxane and vitrimer whose viscosity has been reduced by heating, or creating a film by coating the reinforcing fibers with a composition containing polyrotaxane and vitrimer on a release paper or the like, then overlapping the film on both sides or one side of the reinforcing fibers and impregnating the reinforcing fibers with the composition containing polyrotaxane and vitrimer by heating and pressurizing. The hot melt method is preferred because there is virtually no residual solvent in the prepreg.

[0081] A fiber-reinforced composite material is manufactured by applying a composition containing polyrotaxane and vitrimer to reinforcing fibers, followed by heat treatment to remove the solvent contained in the composition and drying. This heat treatment is thought to promote the formation of covalent bonds between the polyrotaxane and the functional groups on the surface of the reinforcing fibers, and the bonding between the polyrotaxane and the vitrimer, thereby improving the adhesion between the reinforcing fibers and the vitrimer. Preferably, the heat treatment conditions are a temperature range of 130°C to 260°C, more preferably 160°C to 260°C, for 30 to 1440 seconds. When the temperature is 130°C or higher and the duration is 30 seconds or longer, the water or organic solvent that dissolved or dispersed the polyrotaxane can be sufficiently removed. When the temperature is 260°C or lower and the duration is 1440 seconds or less, the operating costs and safety are excellent.

[0082] Heat treatment can be performed using heating devices such as ovens and autoclaves, but it can also be performed by microwave irradiation and / or infrared irradiation. When reinforcing fibers are heat-treated by microwave irradiation and / or infrared irradiation, the reinforcing fibers can be heated to the desired temperature in a short time. In addition, since the inside of the reinforcing fibers can be heated quickly by microwave irradiation and / or infrared irradiation, the temperature difference between the inside and outside of the reinforcing fiber bundle can be reduced.

[0083] Fiber-reinforced composite materials can be produced by laminating the obtained composite materials and then heat-curing a composition containing polyrotaxane and vitrimer while applying pressure to the laminate. Examples of methods for applying heat and pressure include press molding, autoclave molding, bagging molding, wrapping tape method, internal pressure molding, and vacuum pressure molding.

[0084] This disclosure provides a method for recycling any of the fiber-reinforced composite materials described above. The method for recycling any of the fiber-reinforced composite materials described above includes heating the fiber-reinforced composite material in a solvent to 200°C or below, and reducing the percentage of vitrimer remaining on the reinforcing fibers to 50% or less within 24 hours from the start of heating.

[0085] Examples of solvents include ethylene glycol, but are not limited to these.

[0086] The vitrimer used in the fiber-reinforced composite material of the embodiments of this disclosure has a low melting temperature and can be separated from the reinforcing fibers at low temperatures and in a short period of time. Therefore, with this configuration, the fiber-reinforced composite material can be recovered at low temperatures and in a short period of time, while saving energy.

[0087] In some embodiments, a method for recycling fiber-reinforced composite materials includes heating the fiber-reinforced composite material described above in a solvent to 50-150°C, and reducing the percentage of vitrimer remaining on the reinforcing fibers within 24 hours from the start of heating to 50% or less.

[0088] In some embodiments, a method for recycling fiber-reinforced composite materials includes heating the fiber-reinforced composite material described above in a solvent to 50-150°C, and reducing the percentage of vitrimer remaining on the reinforcing fibers within 24 hours from the start of heating to 10% or less.

[0089] The fiber-reinforced composite material of this disclosure possesses high toughness and mild chemical decomposition compared to general fiber-reinforced resins and vitrimer resin-reinforced fibers. Despite being strong and resistant to breakage during use, the fiber-reinforced composite material of this disclosure allows for efficient separation of composite fibers and resin components at low energy (low temperature) and in a short time under specific conditions. Therefore, the fiber-reinforced composite material of this disclosure enables high durability and high recyclability when applied as a structural material in various technological fields, making it a useful material modification technology for realizing a resource-recycling society.

[0090] The fiber-reinforced composite materials of this disclosure are used, for example, in the housings and internal components such as trays and chassis of electrical and electronic equipment such as personal computers, displays, office automation equipment, mobile phones, personal digital assistants, facsimile machines, compact discs, portable MD players, portable radio cassette players, PDAs (personal digital assistants such as electronic organizers), video cameras, digital still cameras, optical equipment, audio equipment, air conditioners, lighting equipment, entertainment products, toys, and other home appliances; as well as in building materials such as mechanical components and panels.Motor parts, alternator terminals, alternator connectors, IC regulators, potentiometer bases for light dew, suspension parts, various valves such as exhaust gas valves, fuel-related parts, various exhaust or intake system pipes, air intake nozzle snorkels, intake manifolds, various arms, various frames, various hinges, various bearings, fuel pumps, gasoline tanks, CNG tanks, engine coolant joints, carburetor main bodies, carburetor spacers, exhaust gas sensors, coolant sensors, oil temperature sensors, brake pad wear sensors, throttle position sensors, crankshaft position sensors, air flow meters, brake pad wear sensors, air conditioning thermostat bases, heating hot air flow control valves, radiator motor brush holders, water pump impellers, turbine vanes, wiper motor related parts, distributors, starter switches, starter relays, transmission wire harnesses, window washer nozzles Examples include automotive or motorcycle-related parts and components such as wheels, air conditioning panel switch boards, fuel-related solenoid valve coils, fuse connectors, battery trays, AT brackets, headlamp supports, pedal housings, steering wheels, door beams, protectors, chassis, frames, armrests, horn terminals, step motor rotors, lamp sockets, lamp reflectors, lamp housings, brake pistons, noise shields, radiator supports, spare tire covers, seat shells, solenoid bobbins, engine oil filters, ignition system cases, undercovers, scuff plates, pillar trims, propeller shafts, wheels, fenders, fascias, bumpers, bumper beams, bonnets, aero parts, platforms, cowl louvers, roofs, instrument panels, spoilers, and various modules; aircraft-related parts or components such as body panels, landing gear pods, winglets, spoilers, edges, rudders, elevators, fairings, and ribs; and body panels, wind turbine blades, etc. In particular, it is preferably used in aircraft components, wind turbine blades, automotive body panels, and housings, trays, and chassis for electronic equipment. ;

[0091] All patent applications and disclosures cited herein are incorporated herein by reference in their entirety.

[0092] The following examples are for illustrative purposes only and are not intended to limit the technical scope of the present invention in any way. Unless otherwise specified, reagents are obtained or prepared from commercially available sources or according to methods commonly used in the art or procedures described in prior art. [Examples]

[0093] Example 1: Manufacturing of fiber-reinforced composite material For the reinforcing fibers, a carbon fiber cloth was used, which was a plain weave of carbon fibers with a nominal modulus of elasticity of 230 GPa. For the resin, a polyrotaxane-containing vitrimer was used, containing 0, 10, or 20 parts by mass of polyrotaxane per 100 parts by mass of the total amount of polyrotaxane and vitrimer (hereinafter, even when the amount of polyrotaxane is 0 parts by mass, it will be conveniently referred to as "polyrotaxane-containing vitrimer"). The mass ratio of carbon fiber to resin was set to 60:40. An intermediate material was prepared by wet-impregnating one layer of carbon fiber cloth with the polyrotaxane-containing vitrimer, and a laminate of a predetermined thickness was prepared by layering these materials. The prepared laminate was heated (180 degrees Celsius for 4 hours) and pressurized (0.5 MPa) in an autoclave under vacuum (-0.1 MPa) to produce a fiber-reinforced composite material.

[0094] Example 2: Fracture Toughness Test During the fabrication of fiber-reinforced composite materials, a release film was inserted as an intermediate layer beforehand. By machining the composite material laminate based on this film, test specimens with artificial cracks were prepared (Figures 1A and 2A). In the DCB test shown in Figure 1A, a perforated aluminum jig for applying load was bonded to the test specimen, and the fracture toughness value under mode I load was determined by applying load-unload loads through the aluminum jig using pins. The test method conforms to the JIS K7086 standard. Figure 1B shows the relationship between the fracture toughness value under mode I load obtained from the DCB test and the polyrotaxane content. It can be seen that the fracture toughness value under mode I load improves with increasing polyrotaxane content. In the ENF test shown in Figure 2A, the fracture toughness value under mode II loading was determined by applying a three-point bending load to a specimen with an artificial crack. The test method conforms to the JIS K7086 standard. Figure 2B shows the relationship between the fracture toughness value under mode II loading obtained from the ENF test and the polyrotaxane content. It can be seen that the fracture toughness value under mode II loading improves with increasing polyrotaxane content. There have been no previous examples of applying polyrotaxane-containing vitrimers to CFRP. Simply mixing a small amount of polyrotaxane during prepolymer preparation resulted in approximately 2.5 times higher fracture toughness and approximately 3 times faster chemical decomposition compared to conventional CFRP.

[0095] Example 3: Examination of the validity of fracture toughness values Figure 3A shows the fracture toughness G of carbon fiber alone (point A), a composite material of carbon fiber and polyrotaxane (point B), a composite material of carbon fiber and vitrimer (point C), and a composite material of carbon fiber, vitrimer, and polyrotaxane (points X1 and X2, 10 parts by mass and 20 parts by mass of polyrotaxane, respectively). IC This is the graph. The carbon fibers in each sample are the same. Delamination strength G in the opening mode at points A, B, C, X1, and X2 IC and interlaminar toughness G in in-plane shear mode IIC Each was measured according to JIS K7086. Delamination strength G for each opening mode at points A, B, C, X1, and X2 ICThe values ​​were 0.02, 0.11, 0.52, 0.96, and 1.35. The increments of X1 and X2 relative to point A are much larger than the sum of the increments of point B relative to point A and the increments of point C relative to point A. Fracture toughness G provided by the combination of carbon fiber, vitrimer, and polyrotaxane. IC This is an unexpected effect.

[0096] Figure 3B shows the fracture toughness G of carbon fiber alone (point A), a composite material of carbon fiber and polyrotaxane (point B), a composite material of carbon fiber and vitrimer (point C), and a composite material of carbon fiber, vitrimer, and polyrotaxane (points X1, X2). IIC This is the graph. The carbon fibers in each sample are the same. Interlaminar toughness G of each in-plane shear mode at points A, B, C, X1, and X2 IIC The values ​​were 0.02, 0.54, 1.97, 2.45, and 2.74. The increment of X1 relative to point A was about the same as the sum of the increments of point B relative to point A and point C relative to point A, while the increment of X2 relative to point A was much larger than the sum of the increments of point B relative to point A and point C relative to point A. Fracture toughness G resulting from the combination of carbon fiber, vitrimer, and polyrotaxane. IIC This is an unexpected effect.

[0097] Figure 3C shows the fracture toughness values ​​for carbon fiber alone (point A), a composite material of carbon fiber and polyrotaxane (point B), and three types of CFRP (points C, X1, X2). At points A and B, the fracture toughness values ​​are very close, but the composite material (CFRP formation by adding vitrimer, points C, X1, X2) has a higher value than points A and B because it causes fiber bridging during crack propagation. In particular, the polyrotaxane-impregnated vitrimer (points X1, X2) shows a high fiber bridging effect during crack propagation.

[0098] Figure 3D shows the relationship between the sum and difference of fracture toughness values ​​for carbon fiber alone (point A), a composite material of carbon fiber and polyrotaxane (point B), and three types of CFRP (points C, X1, X2). Even for the resin alone (point A), the relationship between the sum and difference of fracture toughness values ​​shows a clear correlation, indicating that an increase in the sum of fracture toughness values ​​leads to an increase in the difference of fracture toughness values.

[0099] Figure 4A shows the relationship between the fracture toughness values ​​under mode I loading obtained from the DCB test and the fracture toughness values ​​under mode II loading obtained from the ENF test. The points enclosed by the dashed lines in the figure represent the relationship between the fracture toughness values ​​under mode I loading and mode II loading for general-purpose CFRP measured using the same method. General-purpose CFRP has different resin types, and there is a large variation because some resin types increase the fracture toughness value under mode I loading and others increase the fracture toughness value under mode II loading. However, generally, there is a tendency for the fracture toughness value under mode II loading to increase as the fracture toughness value under mode I loading increases. In polyrotaxane-free vitrimer CFRP (point C), polyrotaxane 10% by mass-impregnated vitrimer CFRP (point X1), and polyrotaxane 20% by mass-impregnated vitrimer CFRP (point X2), similar to general-purpose CFRP, the fracture toughness value under mode I loading increased, which in turn increased the fracture toughness value under mode II loading, and these values ​​were significantly higher than those of general-purpose CFRP.

[0100] Figure 4B shows the relationship between the sum and difference of fracture toughness values ​​under Mode II loading and under Mode I loading. While the comparison of fracture toughness values ​​for general-purpose CFRP (enclosed by the dashed line) showed considerable variation and a general trend, the relationship between the sum and difference of fracture toughness values ​​clearly showed a relationship even for general-purpose CFRP, indicating that an increase in the sum of fracture toughness values ​​leads to an increase in the difference. Similarly, points C, X1, and X2 in the figure can be seen as being on the extension of the relationship between the sum and difference of fracture toughness values ​​for general-purpose CFRP.

[0101] Example 4: Recycling of fiber-reinforced composite materials Samples for chemical decomposition testing were cut from the 1 mm thick CFRP prepared in Example 1. The chemical decomposition test was performed by exchanging the ester bonds of the vitrimer resin with the hydroxyl groups of ethylene glycol. The CFRP test pieces were immersed in ethylene glycol containing 0.1% by weight of diazabicycloundecene (DBU) and stirred at 100°C. The resin retention rate of the CFRP was calculated from the weight change over time to confirm the trend of chemical decomposition. In this example, (1) CFRP containing vitrimer resin without polyrotaxane and (2) CFRP containing vitrimer resin containing polyrotaxane at a ratio of 10% by mass of the uncured composition were used. Figure 5 shows photographs of polyrotaxane-containing CFRP before and after chemical decomposition. Due to the stirring conditions, the carbon fibers (CF) could not maintain their cross-like state, but were successfully recovered in fibrous form. The fiber length was maintained. Figure 6 shows a graph plotting the resin retention rate on the vertical axis and time on the horizontal axis. The 50% decomposition time for polyrotaxane-containing CFRP was 5 hours, and the 100% decomposition time was 50 hours. This indicates decomposition approximately three times faster than that of polyrotaxane-free CFRP. Figure 7 shows scanning electron microscope (SEM) images of individual carbon fibers and carbon fibers recovered from CFRP chemically decomposed for 70 hours. In polyrotaxane-free CFRP, residual resin can be seen on the surface of the carbon fibers, but in polyrotaxane-containing CFRP, the same surface structure as individual carbon fibers was observed, and no residual resin was seen. In other words, it is suggested that by using a polyrotaxane-containing vitrimer to create carbon fiber composite materials, complete chemical decomposition is possible with lower energy and in a shorter time.

Claims

1. A fiber-reinforced composite material comprising reinforcing fibers, a polyrotaxane having a cyclic molecule modified by a graft chain having a first reactive functional group, and a vitrimer having a second reactive functional group capable of undergoing a bond exchange reaction with the first reactive functional group of the cyclic molecule of the polyrotaxane, A fiber-reinforced composite material comprising 1 to 70 parts by mass of reinforcing fibers, 1 to 20 parts by mass of polyrotaxane, and 10 to 98 parts by mass of vitrimer, with a total content of 100 parts by mass of the reinforcing fibers, the polyrotaxane, and the vitrimer, wherein the mass ratio of polyrotaxane to vitrimer is 1 to 40:60 to 99.

2. The fiber-reinforced composite material according to claim 1, wherein the reinforcing fiber is coated with a composition containing polyrotaxane and vitrimer.

3. The fiber-reinforced composite material according to claim 1, wherein the mass ratio of polyrotaxane to vitrimer is 10 to 40:70 to 90.

4. G measured according to JIS K7086 ＩＣ The value and G measured according to JIS K7086 IIＣ The value of G IIＣ -G ＩＣ If 2 or more, and G ＩＣ +G IIＣ A fiber-reinforced composite material according to claim 1, satisfying four or more of the following conditions.

5. A fiber-reinforced composite material according to any one of claims 1 to 4, wherein the reinforcing fibers include carbon fibers or glass fibers.

6. The fiber-reinforced composite material according to any one of claims 1 to 4, wherein the vitrimer contains a thermosetting resin.

7. A method for manufacturing fiber-reinforced composite materials, Applying a composition containing polyrotaxane and vitrimer to the reinforcing fiber, Heating the reinforcing fiber to which the composition has been applied. A method that includes this.

8. A method for recycling fiber-reinforced composite materials, A method comprising heating a fiber-reinforced composite material according to any one of claims 1 to 4 in a solvent to 200°C or below, and reducing the percentage of vitrimer remaining on the reinforcing fibers within 24 hours from the start of heating to 50% or less.

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