Fiber-reinforced composite material and method for manufacturing same

Abstract

The present invention develops a fiber-reinforced composite material containing bagworm silk thread as a reinforcing fiber, the fiber-reinforced composite material being capable of maintaining or enhancing physical properties including strength, elastic modulus, and elongation of a polymer matrix without using bagworm long silk thread.　Provided is a fiber-reinforced composite material containing bagworm silk thread having a major axis fiber length of less than 1 mm as a reinforcing fiber.

Description

Fiber Reinforced Composite Material and Method for Producing the Same

[0001] The present invention relates to a fiber reinforced composite material containing short fiber wasp silk yarn as a reinforcing fiber, and a method for producing the same.

[0002] Fiber reinforced composite materials obtained by compounding a matrix material and reinforcing fibers typified by carbon fiber reinforced plastics (CFRP: Carbon Fiber-Reinforced Plastics) and glass fiber reinforced plastics (GFRP: Glass Fiber-Reinforced Plastics) are materials that are lightweight and have high strength and elasticity. Such properties are brought about by blending high-strength and low-elongation reinforcing fibers with a low-strength and high-elongation matrix material, and thus are largely based on the mechanical properties of reinforcing fibers such as carbon fibers and glass fibers. In particular, carbon fibers are known to have mechanical properties approximately 10 times that of iron in terms of specific strength obtained by dividing the strength by the density of the material (Non-Patent Document 1). Due to such mechanical properties and chemical properties such as non-corrosion, fiber reinforced composite materials are used as alternative materials to metals in various fields ranging from sports and leisure goods, automobiles, houses, buildings, to aircraft.

[0003] However, all of the conventional reinforcing fibers used in fiber reinforced composite materials have had the common property of "not stretching". Also, even if the matrix material had high elongation, when made into a fiber reinforced composite material, its elongation would necessarily decrease due to the reinforcing fibers. This property of the reinforcing fibers has been the main cause of the "brittleness" of the entire fiber reinforced composite material and "peeling" at the interface between the reinforcing fibers and the matrix material. In particular, the more flexible the matrix material was, the more serious the peeling of the reinforcing fibers in the fiber reinforced composite material became.

[0004] Therefore, attempts have been made to solve this problem by using fibers having high strength, high elastic modulus, and elongation properties as next-generation reinforcing fibers in fiber reinforced composite materials. For example, spider-derived silk (often referred to as "spider silk" in this specification) is currently attracting attention as a reinforcing fiber that is very tough and has elongation properties (Non-Patent Document 2).

[0005] However, when spider silk is actually used as a reinforcing fiber, there are many practical issues that need to be resolved. For example, spiders are difficult to cultivate in large quantities because it is difficult to harvest large amounts of silk from them, and mass production is not possible, resulting in high production costs. Currently, attempts are being made to solve this problem by using genetic modification technology to produce spider silk from E. coli or silkworms (Patent Document 1 and Non-Patent Document 3). However, since the E. coli and silkworms used to produce spider silk are genetically modified organisms, they can only be cultured and raised in facilities equipped with specific equipment, and mass production requires large-scale production facilities, which also presents a new problem of increased maintenance and management burden. In addition, the spider silk protein expressed in E. coli is in liquid form, so a process to convert it into fibers is necessary, but at present, a fiber conversion process that reproduces the mechanical properties of natural fibers has not been found. Furthermore, there is also the problem of increased production costs due to the large number of processes.

[0006] To solve the above problems, the present inventors developed a fiber-reinforced composite material using silk threads spun by bagworms (bagworm silk) as reinforcing fibers, as described in Patent Document 2. Bagworm silk possesses a good balance of strength and elongation properties, and has mechanically superior characteristics compared to silkworm silk and spider silk. For example, the bagworm silk of the brown bagworm (Eumeta minuscula) has an elastic modulus 3.5 times that of silkworm silk and 2.5 times that of the golden orb-weaver spider (Nephila clavata) (Non-Patent Documents 4 and 5). Furthermore, the present inventors have revealed that the bagworm silk of the giant bagworm (Eumeta japonica) has similar mechanical properties when compared to silkworm silk and spider silk derived from orb-weaver spiders (Patent Document 2). For example, its elastic modulus was approximately 5 times that of silkworm silk and more than 3 times that of spider silk. Furthermore, its breaking strength was more than three times that of silkworm silk and about twice that of spider silk, while its breaking elongation was more than 1.3 times that of silkworm silk and nearly comparable to that of spider silk. In particular, its toughness was more than four times that of silkworm silk and more than 1.7 times that of spider silk, demonstrating that it exhibits the highest level of toughness among natural fibers.

[0007] In the fiber-reinforced composite material disclosed in Patent Document 2, the use of cocoon silk threads as reinforcing fibers significantly improved the problem of reduced elongation caused by conventional reinforcing fiber formulations such as CFRP. Furthermore, it was found that the elastic modulus improved by more than 10 times compared to that of the polymer matrix alone.

[0008] WO2012 / 165477 JP 2019-044117 JP 2018-197415

[0009] Toru Hiramatsu, A Comprehensive Introduction to Carbon Fiber Composites, Nikkan Kogyo Shimbun, 2015, Chapter 1. Mathijsen D., 2016, Reinforced Plastics, 60: 38-44. Kuwana Y, et al., 2014, PLoS One, DOI: 10.1371 / journal.pone.0105325. Shigeyoshi Osaki, 2002, Journal of the Textile Society of Japan (Textiles and Industry), 58: 74-78. Gosline JM et al., 1999, J. Exp. Biol. 202, 3295-3303.

[0010] In the fiber-reinforced composite material disclosed in Patent Document 2 (JP 2019-044117 A), long silk threads were mainly used. For example, in the example in Patent Document 2, a bagworm silk thread with a total length of approximately 150m was used as the reinforcing fiber. Although a method for producing long bagworm silk threads has been established by the method disclosed in Patent Document 3, etc., the problems of the time and cost required for harvesting the threads were unavoidable.

[0011] The object of the present invention is to develop and provide a fiber-reinforced composite material that uses bagworm silk as a reinforcing fiber, and that can maintain the physical properties of strength, elastic modulus, and elongation without using long lengths of bagworm silk.

[0012] To solve the above problems, the inventors considered using short cocoon silk threads as reinforcing fibers. With short cocoon silk threads, there is no need to prepare long silk threads, and even if the cocoon silk threads are intricately tangled like a mass of silk threads, they can be easily prepared by cutting them. However, there are concerns that shortening the fiber length will not only make it impossible to maintain strength, elastic modulus, and elongation, but may even decrease them.

[0013] However, in reality, even when extremely short cocoon silk threads less than 1 mm in length were used as reinforcing fibers, the elongation was maintained, contrary to expectations. Furthermore, surprisingly, the strength was actually increased, and it became clear that the modulus of elasticity also increased with increasing amounts of cocoon silk thread. This invention is based on the above research results and includes the following:

[0014] (1) Reinforcing fibers for fiber-reinforced composite materials, comprising cocoon silk threads having a long axis fiber length of less than 1 mm. (2) Fiber-reinforced composite material comprising reinforcing fibers including cocoon silk threads having a long axis fiber length of less than 1 mm, and a polymer matrix. (3) The fiber-reinforced composite material according to (2), further comprising organic fibers, inorganic fibers, or a combination thereof. (4) The fiber-reinforced composite material according to (2) or (3), wherein the polymer matrix is ​​resin, glue, starch, agar, or a combination thereof. (5) The fiber-reinforced composite material according to any one of (2) to (4), wherein the mass fraction of cocoon silk threads in the fiber-reinforced composite material is 0.5% to 50%. (6) A method for producing a fiber-reinforced composite material, comprising a contact step of bringing the reinforcing fibers into contact with the polymer matrix, wherein the reinforcing fibers include cocoon silk threads with a long axis fiber length of less than 1 mm. (7) The method for producing a fiber-reinforced composite material according to (6), comprising a molding step of shaping the reinforcing fibers and / or the polymer matrix into a desired shape. (8) The manufacturing method according to (7), wherein the molding step uses a mold. (9) The manufacturing method according to (7) or (8), further comprising a curing step for promoting and / or completing the polymerization reaction of the polymer matrix after the molding step. (10) The manufacturing method according to (8) or (9), further comprising a demolding step for removing the completed fiber-reinforced composite material from the mold. This specification encompasses the disclosures of Japanese Patent Application No. 2024-201242, which forms the basis of the priority of this application.

[0015] The present invention provides a fiber-reinforced composite material that contains bagworm silk as a reinforcing fiber and has properties of strength, elastic modulus, and elongation, while maintaining elongation and further improving strength and elastic modulus.

[0016] This figure shows the relationship between displacement strain and stress based on the length of each long-axis fiber of short-fiber cocoon silk in fiber-reinforced composite materials. In the figure, a is PBS alone, b is a fiber-reinforced composite material consisting of PBS + cocoon silk with a long-axis fiber length of 0.1 mm, c is a fiber-reinforced composite material consisting of PBS + cocoon silk with a long-axis fiber length of 0.5 mm, and d is a fiber-reinforced composite material consisting of PBS + cocoon silk with a long-axis fiber length of 0.9 mm. This figure shows the relationship between displacement strain and stress based on the content of short-fiber cocoon silk in fiber-reinforced composite materials. In the figure, a is PBS alone, b is a fiber-reinforced composite material consisting of PBS + cocoon silk with a content of 1%, c is a fiber-reinforced composite material consisting of PBS + cocoon silk with a content of 2%, d is a fiber-reinforced composite material consisting of PBS + cocoon silk with a content of 4%, and e is a fiber-reinforced composite material consisting of PBS + cocoon silk with a content of 10%.

[0017] 1. Reinforcement Fiber 1-1. Overview The first aspect of the present invention is a reinforcement fiber. The reinforcement fiber of the present invention is a reinforcement fiber for fiber-reinforced composite materials and consists of short silk filament with a major axial fiber length of less than 1 mm. By using the reinforcement fiber of the present invention as a reinforcement fiber for fiber-reinforced composite materials, the elongation, elastic modulus, and strength of the fiber-reinforced composite material can be enhanced.

[0018] 1-2. Definitions The terms frequently used in this specification are defined below. "Bagworm" refers to the larvae of moths belonging to the family Psychidae in the order Lepidoptera. Moths of the Psychidae family are distributed all over the world, but all larvae (bagworms) live in a nest made of natural materials such as leaf fragments and twigs spun by themselves, throughout their entire larval stage. The nest is a sac-like structure that can enclose the entire body and takes the form of a spindle, cylindrical, or conical shape. Bagworms usually remain hidden inside this nest, always moving with the nest when feeding or moving, and pupation also generally takes place inside the nest.

[0019] In this specification, "bagworm silk" refers to the silk spun by bagworms. Unless otherwise specified, the term "silk" in this specification refers to bagworm silk.

[0020] In this specification, "silk" refers to the protein-based threads spun by insect larvae and adults for purposes such as nesting, movement, anchoring, cocooning, and prey capture. In this specification, silk includes monofilaments, spun fibers, spun silk, and aggregated fibers.

[0021] In this specification, "monofiber" refers to the smallest unit of filament (monofilament) yarn that constitutes silk yarn, and the fibrous components such as fibroin protein obtained by removing coating components such as sericin protein from the spun silk fibers described later. Monofibers do not exist in their natural state in principle and are obtained by scouring the spun silk fibers.

[0022] In this specification, "spun silk fibers" refer to silk threads produced by insects. For example, the spinned silk fibers of bagworms are composed of difilaments, which are pairs of single fibers joined together by a coating component.

[0023] In this specification, "spun silk" refers to spun yarn obtained by spinning relatively short silk threads.

[0024] In this specification, "composite fiber" refers to a fiber composed of multiple bundles of silk fibers, also known as a multifilament. The composite fibers described herein consist of single fibers, spun fibers, spun yarns, or combinations thereof. The composite fibers described herein also include those composed solely of silk from a single species, such as bagworm silk, and mixed fibers composed of multiple types of silk from different origins, such as bagworm silk and silkworm silk. Furthermore, composite fibers include not only twisted fibers but also untwisted fibers.

[0025] Furthermore, in addition to the structural classification described above, bagworm silk can be classified into nest silk and scaffold silk based on its spinning morphology. In this specification, when simply referred to as bagworm silk, it encompasses both scaffold silk and nest silk.

[0026] In this specification, "scaffolding silk" refers to silk spun by bagworms for the purpose of movement, and it functions as a scaffold to prevent them from falling from branches, leaves, etc., while moving. Bagworms use this scaffolding silk as a foothold, and move in the direction of travel by hooking the claws of both their legs onto it. To make it easier for bagworms to hook their left and right legs, and to distribute the load on the silk and the fixing points of the silk to both sides, the scaffolding silk is spun in a zigzag pattern. Scaffolding silk is thicker and mechanically stronger than the nesting silk described later.

[0027] In this specification, "nest silk" refers to the silk that makes up the nest, which is spun to bind together leaf fragments and twigs, and to create a comfortable environment on the inner wall of the nest, which is the living area.

[0028] A "fiber-reinforced composite material" refers to a material in which two or more different materials, namely reinforcing fibers and a matrix material, are integrated while remaining separate and not fused with each other. Examples include prepregs, which are made by impregnating sheet-like reinforcing fibers with resin, and pellets, which are made by mixing and dispersing short reinforcing fibers in a polymer matrix. Specific examples of prepregs include carbon fiber-reinforced plastics (CFRP) (often referred to as "CFRP prepreg" in this specification), which are made by impregnating carbon fibers with resin; glass fiber-reinforced plastics (GFRP) (often referred to as "GFRP prepreg" in this specification), which are made by impregnating glass fibers with resin; and aramid fiber-reinforced plastics (AFRP) (often referred to as "AFRP prepreg" in this specification), which are made by impregnating aramid fibers with resin.

[0029] In this specification, "reinforcement fiber" refers to the fibrous base material in a fiber-reinforced composite material. Generally, a reinforcement fiber is a reinforcing material that imparts at least one of strength, modulus of elasticity, and elongation to a fiber-reinforced composite material. The reinforcement fiber may be an inorganic fiber, an organic fiber, or a combination thereof.

[0030] In this specification, "matrix" is also referred to as "base material" and refers to the supporting base material in a fiber-reinforced composite material. In fiber-reinforced composite materials, the base material is usually the component to which strength and other properties are imparted. However, in this specification, the reinforcing fibers not only act as reinforcing materials themselves, but the base material can also act as a reinforcing material, imparting strength to the reinforcing fibers by filling the spaces between them. In other words, in the fiber-reinforced composite material of the present invention, each constituent material enhances the advantages of the others and / or complements the disadvantages of the others. As a result, a fiber-reinforced composite material with new properties not present in the original materials can be obtained.

[0031] In this specification, "polymer matrix" means a base material consisting of organic polymers and / or inorganic polymers.

[0032] 1-3. Structure The reinforcing fiber of the present invention is characterized in that, in principle, it consists of extremely short short fibers of cocoon silk thread, the long axis fiber length being less than 1 mm.

[0033] The type of bagworm moth from which the bagworm silk thread used as a reinforcing fiber in this invention originates is not limited. For example, the Pyrocephalidae family includes genera such as Acanthopsyche, Anatolopsyche, Bacotia, Bambalina, Canephora, Chalioides, Dahlica, Diplodoma, Eumeta, Eumasia, Kozhantshikovia, Mahasena, Nipponopsyche, Paranarychia, Proutia, Psyche, Pteroma, Siederia, Striglocyrbasia, Taleporia, Theriodopteryx, and Trigonodoma, and any species belonging to any of these genera may be used. Specific examples of bagworm moth species include the giant bagworm (Eumeta japonica), the small bagworm (Eumeta minuscula), and the common bagworm (Nipponopsyche fuscescens). Furthermore, the age of the larva (bagworm) that produces the silk thread may be at any stage, and the sex of the larva is not a factor. However, if the goal is to obtain thicker and longer bagworm silk threads, larger bagworms are preferable. For example, within the Psychidae family, larger species are preferable. Therefore, from the viewpoint of obtaining thicker and longer bagworm silk threads, the large bagworm moth and the brown bagworm moth are suitable species for use in this invention. Furthermore, within the same species, the final instar larva is preferable, and even more preferable are the larger females.

[0034] The bagworm silk used as a reinforcing fiber may be either scaffolding silk or nest silk, or a mixture of both. It may also be a single fiber, spinning fiber, or composite fiber, or a mixture of two or more of these.

[0035] The bagworm silk used as a reinforcing fiber consists of short fibers. In this specification, "short fiber" refers to a fiber (silk thread) whose major axis length, i.e., major axis fiber length, is less than 1 mm. There is no lower limit, but it should be 0.01 mm or more. Therefore, the major axis fiber length range of the short fibers is preferably 0.01 mm or more and less than 1 mm, 0.05 mm or more and 0.95 mm or less, 0.08 mm or more and 0.90 mm or less, 0.10 mm or more and 0.85 mm or less, 0.20 mm or more and 0.80 mm or less, 0.25 mm or more and 0.75 mm or less, 0.30 mm or more and 0.70 mm or less, 0.35 mm or more and 0.65 mm or less, 0.40 mm or more and 0.60 mm or less, or 0.45 mm or more and 0.55 mm or less.

[0036] Each bagworm silk thread constituting the short fiber group as a reinforcing fiber consists of short fibers that substantially do not contain any that are 1 mm or longer. Each short fiber constituting the short fiber group may have the same major axis fiber length, or it may be a combination of different major axis fiber lengths. For example, when using a short fiber group of bagworm silk threads with a major axis fiber length of 0.5 mm as a reinforcing fiber, it is not necessary for all major axis fiber lengths in the group to be exactly 0.5 mm. One specific example is when preparing 0.5 mm short bagworm silk threads using a cutting machine. Generally, even if the cutting length is set on the cutting machine, it is difficult to cut the major axis fiber length of all short fibers constituting the short fiber group to the set length. Therefore, it is sufficient that the most abundant major axis fiber length in the short fiber group is 0.5 mm, and it is acceptable for bagworm silk threads with major axis fiber lengths of 0.1 mm or 0.9 mm to be mixed in. Similarly, when using a collection of bagworm silk short fibers with a major axis fiber length of 0.9 mm as a reinforcing fiber, it is sufficient that the most abundant major axis fiber length in the collection of short fibers is 0.9 mm. Even if bagworm silk fibers with a major axis fiber length exceeding the above range of short fibers, for example 1.3 mm, are mixed in, it is acceptable as long as it does not affect the effects of the present invention.

[0037] 2. Fiber-reinforced composite materials 2-1. Overview A second aspect of the present invention is a fiber-reinforced composite material. The fiber-reinforced composite material of the present invention is characterized in that it uses reinforcing fibers for fiber-reinforced composite materials described in the first aspect, i.e., reinforcing fibers made of short-fiber cocoon silk threads, as a fiber base material. According to the present invention, it is possible to provide a fiber-reinforced composite material having high strength, high modulus of elasticity, and elongation properties.

[0038] 2-2. Composition 2-2-1. Constituent Components The fiber-reinforced composite material of the present invention contains reinforcing fibers and a polymer matrix as essential constituent components.

[0039] (1) Reinforcement Fibers The reinforcement fibers used in the fiber-reinforced composite material of the present invention are the reinforcement fibers described in the first embodiment above, that is, reinforcement fibers including short-fiber cocoon silk. "Short-fiber cocoon silk" refers to cocoon silk with a major axis fiber length of less than 1 mm, as described above.

[0040] In the fiber-reinforced composite material, the orientation of the short silk filaments is not limited. For example, the long axis of each silk filament may be arranged in any direction.

[0041] The reinforcing fibers used in the fiber-reinforced composite material of the present invention consist substantially only of short-fiber cocoon silk threads, as described above. However, other reinforcing fibers may be further included within a range that does not impede the effects of the present invention. The "range that does not impede the effects of the present invention" refers to a content of reinforcing fibers other than short-fiber cocoon silk threads relative to the total dry mass of reinforcing fibers constituting the fiber-reinforced composite material, for example, 10% or less, 8% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, or 1% or less.

[0042] "Other reinforcing fibers" include cocoon silk threads with a long axis fiber length of 1 mm or more, organic fibers other than cocoon silk threads, and / or inorganic fibers.

[0043] "The minomushi silk yarn with a long-axis fiber length of 1 mm or more" includes, for example, the minomushi silk yarn of long fibers. In this specification, "long fibers" refers to silk yarns with a long-axis fiber length of 1 m or more, 2 m or more, preferably 3 m or more, more preferably 4 m or more, 5 m or more, 6 m or more, 7 m or more, 8 m or more, 9 m or more, 10 m or more, 15 m or more, 20 m or more, 25 m or more, 30 m or more, 34 m or more, 40 m or more, 45 m or more, 50 m or more, 60 m or more, 70 m or more, 80 m or more, 90 m or more, 100 m or more, 110 m or more, 120 m or more. In this specification, the minomushi silk yarn with a long-axis fiber length of 1 mm or more and less than 1 m is referred to as "medium fibers".

[0044] When including the minomushi silk yarn of long fibers, in the fiber reinforced composite material, the orientation of the silk yarn is not limited. A plurality of fiber bundles may be arranged in one direction or in two or more directions.

[0045] As an example of arranging the fiber bundles of the minomushi silk yarn in one direction, when arranging them linearly and arranging them in a plane (UD material), or while forming a continuous loop (course) in the fiber bundles of the minomushi silk yarn, locking it to the loop of adjacent fiber bundles to connect the vertical loops (weaves) to form a plane (sheet), knitted fabrics (knits), etc. can be mentioned.

[0046] As an example of arranging the fiber bundles of the minomushi silk yarn in two directions, textiles such as woven fabrics and braids can be mentioned. A woven fabric is formed by crossing warp yarns and weft yarns to form a plane (sheet). In the case of a woven fabric, it may be a plain weave where the warp and weft are orthogonal to each other, or a twill weave where they cross obliquely. A braid is a combination of a plurality of fibers made into a string-like or belt-like shape, including braided cords, woven cords, knitted cords, etc. As a specific example, for example, a braided cord is formed by arranging a plurality of fibers in a cylindrical shape along a mandrel to form a string-like structure (braided cord).

[0047] Organic fibers other than the silk of the booklice include vegetable natural fibers such as cotton and hemp mainly composed of cellulose, silk obtained from insects such as silkworms (Bombyx mori) or the larvae of moths of the family Saturniidae, animal natural fibers such as spider silk, and synthetic fibers such as aramid, polyamide (including nylon), polyester, polyethylene, acrylic, and rayon. Inorganic fibers include carbon fibers, glass fibers, metal fibers (stainless steel, titanium, copper, aluminum, nickel, iron, tungsten, molybdenum, etc.), and amorphous fibers (ceramic fibers, rock wool, etc.). By combining the silk of the booklice with other reinforcing fibers, a synergistic effect between the reinforcing fibers can be obtained. For example, carbon fibers, which are the reinforcing fibers of CFRP, and glass fibers, which are the reinforcing fibers of GFRP, exhibit extremely high strength and elastic modulus, but have low toughness and are brittle because they do not have the property of elongation. On the other hand, the silk of the booklice also has high strength and elastic modulus, but it is not as high as that of carbon fibers and glass fibers. However, the silk of the booklice has the property of elongation that carbon fibers and glass fibers do not have. Therefore, by combining the silk of the booklice with carbon fibers and / or glass fibers, it is possible to utilize the advantages of both and complement each other's disadvantages as reinforcing fibers. By using a reinforcing fiber obtained by combining the silk of the booklice with carbon fibers and / or glass fibers, a fiber-reinforced composite material having extremely high strength and elastic modulus and the property of elongation can be manufactured.

[0048] (2) Polymer matrix The polymer matrix refers to a base material composed of an organic polymer and / or an inorganic polymer. The polymer matrix used in the fiber-reinforced composite material of the present invention includes either an organic polymer, an inorganic polymer, or both. The organic polymers mentioned here include natural polymers and synthetic polymers.

[0049] Natural polymers are polymers that exist in nature. For example, proteins, polysaccharides, and natural resins are applicable. Specific examples of proteins include glue (including collagen and gelatin). Specific examples of polysaccharides include starch, cellulose, mannan, agar, etc. Further, specific examples of natural resins include lacquer, rosin, latex (natural rubber), shellac, etc.

[0050] Synthetic polymers are polymers obtained by linking monomers through degeneration or addition polymerization reactions, and examples include synthetic resins and synthetic rubbers.

[0051] Synthetic resins are also called plastics. In the fiber-reinforced composite material of the present invention, the synthetic resin used as the polymer matrix may be a thermosetting resin, a thermoplastic resin, or a combination thereof. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, amino resins, and silicone resins. Examples of thermoplastic resins include polyethylene, polypropylene, polyester, polystyrene, polyamide (including nylon), polyvinyl chloride, methacrylic resin, fluororesin, polycarbonate, polyurethane, aromatic polyether ketone resin, polyphenylene sulfide resin, polybutylene succinate, polyethylene succinate, polybutylene terephthalate, polybutylene adipate terephthalate, modified polyphenylene ether, polyacetal, polyvinyl alcohol, polyglycolic acid, polylactic acid, cellulose acetate, polyhydroxyalkanoic acid, polyhydroxybutyric acid, and polycaprolactone. Thermoplastic resins are preferred as the synthetic resin. Among these, polyethylene, polypropylene, polystyrene, polyamide (including nylon), polybutylene succinate, polyhydroxyalkanoic acid, and polylactic acid are preferred.

[0052] Examples of synthetic rubbers include butadiene rubber, chloroprene rubber, styrene-butadiene rubber, isoprene rubber, ethylene-propylene rubber, nitrile rubber, silicone rubber, acrylic rubber, fluororubber, and urethane rubber.

[0053] (3) Component ratio The blending ratio of reinforcing fibers to polymer matrix in the fiber-reinforced composite material of the present invention is preferably a ratio that can impart the properties of the reinforcing fibers, such as high strength, high modulus of elasticity, and elongation, to the polymer matrix, which is the base material. For example, the mass fraction (fiber content) of short silkworm silk threads relative to the total dry mass of the fiber-reinforced composite material is 0.5% to 50%, 0.6% to 40%, 0.7% to 35%, 0.8% to 30%, 0.9% to 25%, 1.0% to 20%, 1.2% to 18%, 1.5% to 15%, 1.8% to 12%, 2.0% to 10%, 2.5% to 8.0%, 3.0% to 7.0%, 3.5% to 6.0%, and 4.0% to 5.0%. In the present invention, 0.5% to 50% is preferred, 0.6% to 40% is more preferred, 0.7% to 30% is even more preferred, 0.8% to 20% is even more preferred, 0.9% to 15% is even more preferred, and 1.0% to 10% is particularly preferred. As shown in Example 2, when the reinforcing fiber is short-fiber cocoon silk, the higher the mass fraction within the above range, the greater the strength, elastic modulus, and elongation. Therefore, the higher the component ratio of short-fiber cocoon silk in the fiber-reinforced composite material, the more preferable it is.

[0054] 2-2-2. Structure The structure of the fiber-reinforced composite material of the present invention, that is, the arrangement of reinforcing fibers and polymer matrix in the fiber-reinforced composite material, is not particularly limited. For example, examples include pellets in which reinforcing fibers made of short cocoon silk are dispersed in and / or on the surface of a polymer matrix, a prepreg in which a liquid polymer matrix is ​​impregnated into a reinforcing fiber sheet made of short cocoon silk, and a state in which a polymer matrix layer and a reinforcing fiber layer made of short cocoon silk are laminated and integrated.

[0055] 2-3. Applications The fiber-reinforced composite material of the present invention uses cocoon silk thread as the reinforcing fiber, thereby providing elongation characteristics not found in conventional fiber-reinforced composite materials such as CFRP and GFRP. Furthermore, its strength has been further enhanced.

[0056] By utilizing these physical properties, the fiber-reinforced composite material of the present invention can be used in various fields as a substitute material in known structures composed of resin, or as a substitute material for conventional fiber-reinforced composite materials. For example, it is suitable for use as a base material for structures that are expected to be subjected to strong impacts. Specifically, examples include base materials for structures in the sports and leisure field, housing field, civil engineering and construction field, transportation equipment field, industrial equipment, and space-related fields.

[0057] In the sports and leisure sector, examples of its use include as a structural component for sports and leisure equipment such as tennis and badminton rackets, hockey and lacrosse sticks, golf shafts, pole vault poles, snowboards, skis, ski poles, climbing poles, bicycle frames, and fishing rods.

[0058] In the housing sector, examples of its use include as a structural element or reinforcement for buildings, as well as as a structural element for bathtubs, septic tanks, sinks, and other similar structures.

[0059] In the field of civil engineering and construction, examples of its use include as a structural element in helmets, seismic reinforcement materials, lightweight building materials, wall and floor reinforcement materials, and truss structural materials.

[0060] In the transportation equipment sector, examples of its use include as a structural component such as bumpers, guards, fuel tanks, frames, rims, and body panels in mobile vehicles such as motorcycles, automobiles, ships, aircraft, helicopters, and drones.

[0061] In industrial equipment, examples of its use include components such as screws, gears, and printed circuit boards, as well as various structural elements such as casings, home appliance parts, and wind turbine blades. In space-related applications, examples of its use include components for rockets and satellites.

[0062] Furthermore, when the reinforcing fibers used are solely cocoon silk, or a combination of cocoon silk and other silk fibers, and the polymer matrix is ​​made of natural organic polymers such as collagen and gelatin, a highly biocompatible fiber-reinforced composite material is obtained. Therefore, it can be used in the medical field as a tissue regeneration substrate or a blood vessel regeneration substrate.

[0063] 3. Method for Manufacturing Fiber-Reinforced Composite Materials 3-1. Overview A third aspect of the present invention is a method for manufacturing fiber-reinforced composite materials. The method of the present invention is the method for manufacturing and / or molding fiber-reinforced composite materials described in the second aspect. According to the manufacturing method of the present invention, fiber-reinforced composite materials containing short-fiber cocoon silk threads can be easily manufactured and molded.

[0064] 3-2. Method The method for producing the fiber-reinforced composite material of the present invention is basically the same as the conventional method for producing fiber-reinforced composites used in CFRP, GFRP, and other FRPs, except that short-fiber cocoon silk yarn is used as the reinforcing fiber.

[0065] While various manufacturing methods are known, the appropriate method should be selected according to the intended use, shape, and other factors.

[0066] For example, a prepreg can be manufactured by impregnating short-fiber cocoon silk yarn, or a nonwoven reinforced fiber sheet made of short-fiber cocoon silk yarn, with a suitable polymer matrix.

[0067] Alternatively, short silk fibers from bagworms can be dispersed in a molten polymer matrix, the two can be kneaded together, and then the mixture can be introduced into a desired mold for curing and molding.

[0068] Alternatively, reinforcing fibers made from short cocoon silk fibers may be dispersed on the surface of a polymer matrix, and then integrated by heat bonding to form a structure consisting of a polymer matrix layer and a reinforcing fiber layer.

[0069] When the polymer matrix is ​​a thermosetting resin, the polymer becomes a semi-cured prepreg with incomplete polymerization. On the other hand, when the polymer matrix is ​​a thermoplastic resin or a natural polymer such as collagen, mixing can be done using a batch mixer or a single-screw or twin-screw extruder, and the mixed resin is processed into strands or pellets before molding.

[0070] Molding methods using the above-mentioned prepregs include sheet winding, press molding, autoclave molding, RTM (Resin Transfer Molding), VaRTM (Vacuum Resin Transfer Molding), SMC (Sheet Molding Compound) molding, vacuum bag molding, hand lay-up molding, and fiber placement molding.

[0071] The "sheet winding molding method" is a molding method in which prepreg is wound around a mandrel and then decored after hardening.

[0072] The "press molding method" is a method of forming a compound or prepreg by placing it in a mold and applying pressure and heat.

[0073] The "autoclave molding method" involves layering prepreg onto a mold, covering it with a bag, removing air and volatile substances from inside the autoclave under vacuum, and then molding it under pressure and heat.

[0074] The "RTM molding method," also known as resin injection molding, is a method in which molten thermosetting resin is introduced under low pressure into a sealed system in which reinforcing fiber preforms are placed inside a mold, and then released after heat curing.

[0075] The "VaRTM molding method" is a type of RTM (Return to Molding) method in which a sealed system with laminated reinforcing fibers is vacuumed, a thermosetting resin is introduced, and after heat curing, the resin is demolded.

[0076] The "SMC molding method" is a method of forming a material by laminating sheet-like material composed of reinforcing fibers and a polymer matrix.

[0077] The "vacuum back molding method" is a method of compression molding by atmospheric pressure by creating a vacuum in a laminated material that has been sealed with a sealed film.

[0078] The "hand lay-up molding method" is a method of manually layering prepreg onto a mold and then curing it.

[0079] The "fiber placement molding method" is a method of layering prepreg, which has been processed into a tape-like shape, onto various three-dimensional molds and then curing the material.

[0080] Methods for molding the strands and pellets after processing include injection molding, extrusion molding, blow molding, calendering, compression molding, and powder molding. Methods for extruding the material into fibrous filaments are also possible.

[0081] Injection molding is a method of forming a product by pouring mixed resin into an injection molding machine, heating it to its melting point, plasticizing it, injecting it into a mold under pressure, and then cooling and solidifying it. Typical injection molding mechanisms include in-line screw type and pre-plasticized type, as well as multi-color molding, sandwich molding, and gas injection molding. There are vertical and horizontal types for injecting the resin into the mold, and injection mechanisms include direct pressure type and torque type.

[0082] The "extrusion molding method" is a method of molding a resin into a specific shape after it has been molten following the mixing process and passing it through a die. Typically, a screw-type extrusion mechanism is used, and depending on the shape of the die, it is possible to mold the material into shapes such as sheets, pipes, films, and filaments. Furthermore, filaments can be further processed using 3D printers, etc.

[0083] "Blow molding" is also known as hollow molding. It is a method of forming a cylindrical shape from molten resin after mixing, then blowing air into the inside to expand it, and finally cooling and solidifying it while it is in close contact with the mold. There are two types of blow molding: a one-stage method in which air is blown in before solidification, and a two-stage method in which air is blown in after solidification and reheating.

[0084] The "calendering method" is a method of rolling out film or sheet material using multiple rolls at the end of the extrusion process.

[0085] The "compression molding method" involves placing a mixed resin into the space between the upper and lower molds, heating the molds themselves to a melted state, then applying pressure to ensure the resin reaches even the smallest details of the mold, and finally cooling and solidifying it.

[0086] The "powder molding method" is a processing method that uses powdered mixed resin and processes it through rotational molding and fluid immersion molding.

[0087] The specific molding methods described above are all known methods in the field of fiber-reinforced composite materials, and can be used as a reference.

[0088] 3-3. Manufacturing Process The manufacturing process for the fiber-reinforced composite material of the present invention includes a contact step as an essential step, and optionally includes a molding step, a curing step, and a demolding step. Each step will be described in detail below.

[0089] (1) Contact Process The "contact process" is an essential process that brings the reinforcing fibers and the polymer matrix into contact. The method of contact is not particularly limited as long as the two components can come into direct contact. The reinforcing fibers may be dispersed, immersed, or impregnated in a molten liquid polymer matrix, or sheets of reinforcing fibers may be sandwiched between sheets of polymer matrix, as in the SMC molding method.

[0090] If the polymer matrix is ​​a thermoplastic resin, it is sufficient to pre-heat it to melt the polymer matrix and make it liquid. The melting temperature will vary depending on the type of polymer matrix used, but it should generally be above the melting point of the polymer matrix and at a temperature at which the viscosity decreases.

[0091] The aforementioned prepreg is made by impregnating a polymer matrix into a sheet (for example, a nonwoven fabric sheet) composed of reinforcing fibers, and the process consists solely of a contact step.

[0092] (2) Molding Process The "molding process" refers to the process of molding the reinforcing fibers and / or polymer matrix, which are components of the fiber-reinforced composite material, into a desired shape. This process is optional and is performed according to the various manufacturing methods and the form, such as prepreg, strand, pellet, or filament.

[0093] In this process, molds such as dies are used, and the material is shaped according to the mold. Reinforcement fibers or prepregs can be added during the molding process as needed. Alternatively, by using a filament, molding can be performed using a 3D printer without the need for a mold.

[0094] The order of the molding process and the aforementioned contact process varies depending on the manufacturing method and is not limited to any particular order. For example, in the aforementioned filament winding molding method, sheet winding molding method, press molding method, autoclave molding method, hand lay-up molding method, fiber placement molding method, injection molding method, extrusion molding method, blow molding method, calendering method, compression molding method, and powder molding method, the molding process is performed after the contact process. On the other hand, in RTM molding and VaRTM molding, the contact process is performed after the molding process because the polymer matrix is ​​introduced into the mold after the reinforcing fiber preform is molded in the mold. Also, in 3D printing, since molding uses filaments, the molding process is performed after the contact process. The order should be carried out according to each manufacturing method.

[0095] (3) Curing process The "curing process" is required after the above process if the polymer matrix is ​​a thermosetting resin, and refers to a process that promotes and / or completes the polymerization reaction of the polymer matrix. Through this process, the polymer matrix hardens, and the fiber-reinforced composite material is completed. The curing process may include a heating step and / or a cooling step.

[0096] The "heating step" is a step in which the polymerization reaction is accelerated and / or completed by heating the polymer matrix. This step is performed when a thermosetting resin is used for the polymer matrix. On the other hand, if the polymer matrix is ​​a thermoplastic resin or a natural polymer, heating will activate the kinetic heat of the molecules, causing softening or melting, so this step may correspond to the contact step or molding step.

[0097] The heating temperature is not particularly limited. It varies depending on the type of polymer matrix used, but is usually within the range of 20°C to 250°C, 23°C to 200°C, 25°C to 180°C, 27°C to 150°C, or 30°C to 120°C. The heating time is related to the heating temperature; generally, the lower the temperature, the longer the time, and the higher the temperature, the shorter the time. It is usually within the range of 0.5 hours to 48 hours, 1 hour to 42 hours, 1.5 hours to 36 hours, 2 hours to 30 hours, 2.5 hours to 24 hours, or 3 hours to 18 hours.

[0098] The "cooling step" is the step of cooling or curing the heated polymer matrix. When a thermosetting resin is used for the polymer matrix, this step is performed when cooling the fiber-reinforced composite material after the thermosetting reaction is completed in the heating step. When a thermoplastic resin or natural polymer is used for the polymer matrix, the heat of motion of the molecules decreases due to cooling, and the polymer matrix hardens, completing the fiber-reinforced composite material.

[0099] There are no specific restrictions on the cooling temperature. While it varies depending on the type of polymer matrix used, it is generally acceptable to cool to 260°C or below, 200°C or below, 180°C or below, 150°C or below, 120°C or below, 100°C or below, 90°C or below, 80°C or below, 70°C or below, 60°C or below, 50°C or below, 40°C or below, 35°C or below, 30°C or below, 27°C or below, 25°C or below, 23°C or below, 20°C or below, 18°C ​​or below, 15°C or below, or 10°C or below. There are no particular restrictions on the lower limit temperature, but it is generally acceptable to cool to around 4°C, 0°C, -10°C, -15°C, or -20°C. The cooling time can be in the range of 0.1 to 1 hour, 0.2 to 0.9 hours, 0.3 to 0.8 hours, 0.4 to 0.7 hours, or 0.5 to 0.6 hours.

[0100] (4) Demolding Process The "demolition process" is the process of removing the fiber-reinforced composite material from the mold after the curing process. Specifically, in this process, the completed fiber-reinforced composite material is removed from the mold and mandrel used during the molding process. The demolding method may be any method known in the field.

[0101] <Example 1: Changes in physical properties of fiber-reinforced composite materials based on the fiber length of short-fiber cocoon silk threads> (Objective) To verify the physical properties of fiber-reinforced composite materials when the long-axis fiber length of the short fibers of cocoon silk threads is changed and used as reinforcing fibers.

[0102] (Method) Bagworms used were larvae of the giant bagworm moth, reared at Kowa Advanced Science Institute, with a long axis length of the nest measuring 10 mm to 15 mm. Bagworm silk was collected using the following method. Approximately 100 bagworms were reared in a cubic rearing container measuring approximately 15 cm x 15 cm x 7 cm in length, width, and height. As multiple bagworms continued to spin silk within the rearing container, the bagworm silk accumulated on the inner surface of the container and was collected. Subsequently, the bagworm silk was cut to a length of approximately 15 mm in the long axis and scouring with a 3% alcalase solution (55°C, overnight) and a 5 mM boiling sodium carbonate aqueous solution. The scouring of the bagworm silk was air-dried and further cut into short fibers with long axis lengths of 0.1 mm, 0.5 mm, and 0.9 mm using a fiber cutting device developed in-house. These short fibers were used as reinforcing fibers for fiber-reinforced composite materials.

[0103] The mass fraction of reinforcing fibers relative to the total mass of fiber-reinforced composite materials (polymer matrix + reinforcing fibers) was standardized to 4% in terms of fiber content.

[0104] Polybutylene succinate (PBS) (Mitsubishi Chemical Corporation) was used as the polymer matrix. To knead the PBS and the reinforcing fibers, the mixture was placed in a kneading and extrusion testing apparatus (Toyo Seiki Co., Ltd.: 3S150) and kneaded at a kneading speed of 50 rpm at 132°C for 21 minutes to produce the FRP resin, which is the fiber-reinforced composite material of the present invention. At the same time, as a negative control, PBS resin without the reinforcing fibers was kneaded under the same conditions to produce PBS alone.

[0105] Next, to prepare test specimens for mechanical testing, dumbbell-shaped test specimens (JIS K7139 A12) were manufactured using a MiniJetPro piston injection molding machine (Thermo Fisher Scientific). The injection molding conditions were: cylinder temperature 150°C, mold temperature 40°C, molding pressure 600 bar, molding time 15 s, holding pressure 300 bar, and cooling time 30 s.

[0106] Mechanical tests were conducted using the obtained test specimens. The mechanical tests were performed as tensile tests using a benchtop precision universal testing machine (Shimadzu Corporation: Autograph AGS-5kNX). The dumbbell test specimens prepared as described above were evaluated using a 5kN load cell at a tensile speed of 20 mm / min.

[0107] (Results) The results are shown in Table 1 and Figure 1.

[0108]

[0109] Figure 1 shows that fiber-reinforced composite materials containing short cocoon silk fibers with long-axis fiber lengths of 0.1 mm (b), 0.5 mm (c), and 0.9 mm (d) exhibited characteristic SS curves compared to PBS alone (a) of the polymer matrix. This indicates that even short cocoon silk fibers less than 1 mm in length impart the physical properties of cocoon silk to the polymer matrix.

[0110] Furthermore, in Table 1, "maximum point test force" refers to the maximum test force generated when a tensile load is applied to the material before it breaks. Generally, a larger value indicates that the material can withstand a stronger force, i.e., it can bear a higher load. From Table 1 and Figure 1, the fiber-reinforced composite material containing short-fiber cocoon silk threads ranging from 0.1 mm to 0.9 mm showed that the maximum point test force was more than 1.3 times greater than that of PBS alone, which is a polymer matrix, for all major fiber lengths. This suggests that using short-fiber cocoon silk threads as reinforcing fibers can enhance the load-bearing capacity of the fiber-reinforced composite material.

[0111] Furthermore, "maximum point stress" refers to the maximum stress generated before fracture. Generally, a larger value indicates greater stress resistance, i.e., higher strength. From Table 1 and Figure 1, fiber-reinforced composite materials containing short-fiber cocoon silk threads ranging from 0.1 mm to 0.9 mm showed a maximum point stress that was more than 1.3 times greater than that of PBS alone (a polymer matrix), for all major fiber lengths. This suggests that the strength of fiber-reinforced composite materials can be enhanced by using short-fiber cocoon silk threads as reinforcing fibers.

[0112] Furthermore, "maximum point displacement strain" refers to the elongation that represents the maximum stress generated before the sample fractures. Generally, a larger value indicates greater elongation.

[0113] The short-fiber cocoon silk used in this embodiment consists of extremely short fibers ranging from 0.1 mm to 0.9 mm in length. Therefore, it was initially anticipated that using this short-fiber cocoon silk as a reinforcing fiber would not impart the elongation properties of long-fiber cocoon silk to the fiber-reinforced composite material.

[0114] However, as shown in Table 1 and Figure 1, in fiber-reinforced composite materials containing short-fiber cocoon silk threads of 0.1 mm to 0.9 mm, the maximum point displacement strain was slightly increased compared to PBS alone. This suggests that even when short-fiber cocoon silk threads are used as reinforcing fibers, it is possible to impart elongation properties to the fiber-reinforced composite material.

[0115] Furthermore, "elastic modulus" is given as the slope of the initial gradient of the stress-strain curve, and generally, a larger value means less deformation under tensile stress and higher rigidity. From Table 1 and Figure 1, fiber-reinforced composite materials containing short cocoon silk fibers of 0.1 mm to 0.9 mm showed an increased elastic modulus of approximately 10% compared to PBS alone. This suggests that even when short cocoon silk fibers are used as reinforcing fibers, the elastic modulus of fiber-reinforced composite materials increases.

[0116] These results suggest that even with cocoon silk threads having a long-axis fiber length of only 0.1 mm to 0.9 mm, using them as reinforcing fibers results in fiber-reinforced composite materials that are more elongated, rigid, and strong (stress-resistant) than polymer matrices alone.

[0117] <Example 2: Changes in physical properties based on the amount of short-fiber cocoon silk yarn blended in fiber-reinforced composite materials> (Objective) To verify the physical properties of fiber-reinforced composite materials when the amount of short fibers of cocoon silk yarn used as reinforcing fibers is changed.

[0118] (Method) The basic procedure is the same as in Example 1. However, in this example, the long axis fiber length of the short fiber cocoon silk used was standardized to 0.5 mm, and the amount added was set to 1%, 2%, 4%, and 10% of the total mass of the fiber-reinforced composite material in terms of the reinforcing fiber content.

[0119] (Results) The results are shown in Table 2 and Figure 2.

[0120]

[0121] In the fiber-reinforced composite material "PBS + short-fiber cocoon silk" of the present invention, an increase in the maximum point test force, maximum point stress, maximum point displacement strain, and elastic modulus was observed with increasing amounts of cocoon silk compared to PBS alone. This suggests that these physical properties increase with a high correlation to the content of short-fiber cocoon silk.

[0122] From the results of Examples 1 and 2 described above, it became clear that even cocoon silk threads with a major axial fiber length of less than 1 mm can be used as reinforcing fibers to impart elongation (displacement strain), stiffness (elastic modulus), and strength (stress) to the polymer matrix, and that these physical properties can be controlled by the amount of cocoon silk threads used.

[0123] <Example 3: Production of a fiber-reinforced composite material using cocoon silk as a reinforcing fiber for polypropylene> (Objective) To verify the physical properties of a fiber-reinforced composite material when short fibers of cocoon silk are used as reinforcing fibers and the target resin is changed to polypropylene.

[0124] (Method) The preparation of short-fiber cocoon silk was carried out in accordance with Example 1. However, polypropylene (PP) (Sun Allomer) was used as the polymer matrix. In addition, in order to knead the PP and reinforcing fibers, each was placed in a kneading and extrusion testing apparatus (Toyo Seiki: 3S150) and kneaded at a kneading speed of 50 rpm at 185°C for 11 minutes to produce an FRP resin. The long-axis fiber length of the short-fiber cocoon silk used at this time was 0.5 mm, and its blending amount was 4% of the total mass of the fiber-reinforced composite material. At the same time, as a negative control, a PP resin without reinforcing fibers was also kneaded under the same conditions to produce pure PP. Subsequently, in order to prepare test specimens for mechanical testing, dumbbell-shaped test specimens (JIS K7139 A12) were prepared using an ORIGINALMIND / INARI P35 injection molding machine. The injection molding conditions were: cylinder temperature 185°C, mold temperature room temperature, extrusion pressure 250 kPa, extrusion time 3 s, holding pressure 150 kPa, and holding time 7 s. Using the obtained test specimens, a mechanical test was performed in the same manner as in Example 1.

[0125] (Results) The results are shown in Table 3.

[0126]

[0127] In the fiber-reinforced composite material of the present invention, "PP + short fiber cocoon silk," an increase was observed in maximum test force, maximum point stress, maximum point displacement strain, and elastic modulus compared to PP alone.

[0128] <Example 4: Production of a fiber-reinforced composite material using cocoon silk as a reinforcing fiber for high-density polyethylene (Objective) To verify the physical properties of a fiber-reinforced composite material when short fibers of cocoon silk are used as reinforcing fibers and the target resin is changed to polyethylene.

[0129] (Method) The preparation of short-fiber cocoon silk was carried out in accordance with Example 1. However, high-density polyethylene (HDPE) (Tosoh) was used as the polymer matrix. In addition, in order to knead the HDPE and reinforcing fibers, each was placed in a kneading and extrusion test apparatus (Toyo Seiki: 3S150) and kneaded at a kneading speed of 50 rpm at 155°C for 11 minutes to produce an FRP resin. The long-axis fiber length of the short-fiber cocoon silk used at this time was 0.5 mm, and its blending amount was 4% of the total mass of the fiber-reinforced composite material. Simultaneously, as a negative control, HDPE resin without reinforcing fibers was kneaded under the same conditions to produce pure PP.

[0130] Next, to prepare test specimens for mechanical testing, dumbbell-shaped test specimens (JIS K7139 A12) were manufactured using an ORIGINALMIND / INARI P35 injection molding machine. The injection molding conditions were as follows: for HDPE resin alone, the cylinder temperature was 155°C, the mold temperature was room temperature, the extrusion pressure was 250kPa, the extrusion time was 3s, the holding pressure was 150kPa, and the holding pressure time was 7s; for the MM silk yarn / HDPE composite material, the cylinder temperature was 165°C, the mold temperature was room temperature, the extrusion pressure was 400kPa, the extrusion time was 3s, the holding pressure was 200kPa, and the holding pressure time was 7s. Using the obtained test specimens, mechanical testing was performed in the same manner as in Example 1.

[0131] (Results) The results are shown in Table 4.

[0132]

[0133] In the fiber-reinforced composite material of the present invention, "HDPE + short fiber cocoon silk," an increase was observed in maximum test force, maximum point stress, maximum point displacement strain, and elastic modulus compared to HDPE alone.

[0134] <Examples 5-14: Production of various fiber-reinforced composite materials containing short-fiber cocoon silk threads as reinforcing fibers> (Objective) To produce various fiber-reinforced composite materials by using the short fibers of cocoon silk threads listed in Table 5 as reinforcing fibers and changing the polymer matrix to various types (Examples 5-14). In the table, PBS represents polybutylene succinate, PE represents polyethylene, PP represents polypropylene, PS represents polystyrene, PHA represents polyhydroxyalkanoic acid, PLA represents polylactic acid, and PA represents polyamide.

[0135]

[0136] (Method) Short-fiber bagworm silk was prepared in accordance with Example 1. The long-axis fiber lengths of the short-fiber bagworm silk are shown in the table. The bagworm silk was cut to the long-axis fiber lengths listed in Table 5, and the polymer matrix listed in Table 5 was used.

[0137] The polymer matrix and reinforcing fibers are kneaded separately in a kneading and extrusion testing apparatus (Toyo Seiki: 3S150) at a kneading speed of 50 rpm under temperature and time conditions corresponding to the polymer matrix to produce the FRP resin. The amount of short-fiber cocoon silk yarn in Table 5 indicates the content of reinforcing fibers relative to the total mass of the fiber-reinforced composite material.

[0138] Furthermore, a polymer matrix without reinforcing fibers is also prepared as a negative control for the mechanical tests by kneading it under the same conditions. The mechanical tests are carried out in the same manner as in Example 1. All publications, patents, and patent applications referenced herein are incorporated herein by direct reference in their entirety.

Claims

1. Reinforcement fibers for fiber-reinforced composite materials, consisting of cocoon silk threads with a long axis fiber length of less than 1 mm.

2. Reinforced fibers containing cocoon silk threads with a long axis fiber length of less than 1 mm, and fiber-reinforced composite materials containing a polymer matrix.

3. The fiber-reinforced composite material according to claim 2, wherein the reinforcing fibers further include organic fibers, inorganic fibers, or a combination thereof.

4. The fiber-reinforced composite material according to claim 2 or 3, wherein the polymer matrix is ​​a resin, glue, starch, agar, or a combination thereof.

5. The fiber-reinforced composite material according to any one of claims 2 to 4, wherein the mass fraction of the bagworm silk in the fiber-reinforced composite material is 0.5% to 50%.

6. A method for producing a fiber-reinforced composite material, comprising a contact step of bringing reinforcing fibers into contact with a polymer matrix, wherein the reinforcing fibers include cocoon silk threads with a long axis fiber length of less than 1 mm.

7. The manufacturing method according to claim 6, comprising a molding step of shaping the reinforcing fibers and / or polymer matrix into a desired shape.

8. The manufacturing method according to claim 7, wherein the molding step uses a mold.

9. The manufacturing method according to claim 7 or 8, comprising a curing step for promoting and / or completing the polymerization reaction of the polymer matrix after the molding step.

10. The manufacturing method according to claim 8 or 9, further comprising a mold release step of removing the completed fiber-reinforced composite material from the mold.

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