Fiber-reinforced composite material and method of manufacturing the same

Abstract

The present application develops and provides a fiber-reinforced composite material having a "stretching" property in addition to high strength and high elastic modulus. In addition, the problem points of brittleness and peeling in the conventional fiber-reinforced composite material are solved. A fiber-reinforced composite material containing a tussah silk as a reinforcing fiber is provided.

Description

[0001] The invention of this application is a divisional application of the application with application number 201880056859.0, invention name “Fiber-reinforced composite material and its manufacturing method”, and application date of August 30, 2018. Technical Field

[0002] The present invention relates to a fiber-reinforced composite material containing silk from a sedge moth as a reinforcing fiber, and a method for producing the same. Background Art

[0003] Fiber-reinforced composite materials, which are formed by combining reinforcing fibers with a base material, are lightweight materials with high strength and elastic modulus, such as carbon fiber reinforced plastics (CFRP: Carbon Fiber-Reinforced Plastics) and glass fiber reinforced plastics (GFRP: Glass Fiber-Reinforced Plastics). Such high strength and elastic modulus are largely based on the mechanical properties of reinforcing fibers such as carbon fiber, glass fiber, and polyaramid fiber. For example, it is known that carbon fiber has mechanical properties about 10 times that of iron in terms of specific strength, which is obtained by dividing the strength by the mass of the raw material (Non-Patent Document 1). Due to such mechanical properties, fiber-reinforced composite materials are used as materials to replace metals in a variety of fields, including sports and leisure products, automobiles, houses, buildings, and aircraft.

[0004] However, conventional reinforcing fibers used in fiber-reinforced composites all share a common property known as "non-stretchability." This property of the reinforcing fibers contributes to the brittleness of fiber-reinforced composites and the delamination that occurs at the interface between the reinforcing fibers and the base material. In particular, the softer the base material, the more severe the delamination problem becomes within the fiber-reinforced composite.

[0005] Therefore, attempts to address this issue are underway by using fibers with high strength, high elastic modulus, and tensile 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), which has very high toughness and tensile properties, is currently attracting attention as a reinforcing fiber (Non-Patent Document 2).

[0006] However, when spider silk is actually used as a reinforcing fiber, there are many aspects that should be addressed in practice. For example, spiders cannot be mass-produced due to the difficulty of mass-raising and collecting large amounts of silk from spiders, resulting in high production costs. Attempts are currently being made to solve this problem by producing spider silk in E. coli or silkworms using genetic recombination technology (Patent Document 1 and Non-Patent Document 3). However, since the E. coli or silkworms used to produce spider silk are genetically recombinant, they can only be cultured or raised in facilities with specified equipment. Large-scale production facilities are required for mass production, and there is a new problem of a heavy burden on maintenance and management. In addition, the spider silk protein expressed in E. coli is liquid, so a process for converting it into fibers is required, but at this stage, no fiberization conversion process has been found that can reproduce the mechanical properties of natural fibers. In addition, there is also the problem of increasing the number of processes and increasing production costs.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: WO2012 / 165477

[0010] Non-patent literature

[0011] Non-patent document 1: Toru Hiramatsu, Introduction to Toru Carbon Carbon Co., Ltd., Nikkan Kogyo Shimbun 2015, Chapter 1.

[0012] Non-Patent Literature 2: Mathijsen D., 2016, Reinforced Plastics, 60: 38-44.

[0013] Non-Patent Literature 3: Kuwana Y, et al., 2014, PLoS One, DOI: 10.1371 / journal.pone.0105325 Summary of the Invention

[0014] Problems to be solved by the invention

[0015] The present invention aims to develop and provide a fiber-reinforced composite material having high strength, high elastic modulus, and the "stretching" properties of conventional fiber-reinforced composite materials. This aims to resolve the brittleness and delamination problems of conventional fiber-reinforced composite materials.

[0016] Means for solving problems

[0017] To address the above-mentioned issues, the present inventors focused on the silk produced by basket worms (alias "bag worms") (often referred to as "bag worm silk" in this specification). Basket worms are a general term for the larvae of moths belonging to the family Psychidae of the order Lepidoptera. They typically lurk in spindle-shaped or cylindrical nests (bag nests) made by binding leaves and branches with silk. They move the nests to feed, remaining within the nest throughout their larval stages.

[0018] This silk from the ground moth has a balanced balance of strength and tensile strength, possessing mechanical properties superior to those of silkworm and spider silk. For example, the elastic modulus of silk from the tea moth Eumeta minuscula is 3.5 times that of silkworm silk and 2.5 times that of spider silk from the Nephila clavata (Osaki Shigeyoshi, 2002, Journal of Textile Society (Textile and Industry), 58:74-78; Gosline JM et al., 1999, J. Exp. Biol. 202, 3295-3303). Furthermore, the inventors have discovered that silk from the ground moth Eumeta japonica exhibits similar mechanical properties when compared to silkworm silk and spider silk from the spider Araneae (Japanese Patent Application No. 2017-110003). For example, the elastic modulus is approximately 5 times that of silkworm silk and more than 3 times that of spider silk. Furthermore, the breaking strength is over three times that of silk and approximately twice that of spider silk, while the breaking elongation is over 1.3 times that of silk, nearly rivaling spider silk. In particular, the toughness was found to be over four times that of silk and over 1.7 times that of spider silk, demonstrating the highest level of toughness among natural fibers.

[0019] In terms of breeding and management, moths also offer advantages over silkworms. For example, silkworms typically feed exclusively on the leaves of species belonging to the genus Morus, such as the chicken mulberry (M. bombycis), the mulberry (M. alba), and the ru mulberry (M. ilhou). Therefore, the breeding area and breeding period are affected by the supply of mulberry leaves and the time when the mulberry leaves bloom. Moths, on the other hand, are polyphagous and have low specificity for leaf bait. Many species can feed on leaves from a wide variety of tree species. Therefore, leaf bait is easily available, and breeding areas are not selective. Furthermore, depending on the species, leaves from some evergreen trees can also be used as leaf bait, so unlike deciduous mulberry trees, leaf bait can be supplied year-round. Moths are also smaller than silkworms, so the breeding space required is less than that of silkworms, making large-scale breeding easier. Therefore, breeding costs can be significantly reduced compared to silkworms.

[0020] The moth also offers advantages over silkworms in productivity. For example, silkworms only produce large amounts of silk when spinning cocoons, whereas all larvae produce cocoons simultaneously. This results in overlapping silk-collecting periods and concentrated labor. On the other hand, moths produce silk repeatedly throughout their larval life, both when building nests and while migrating. This offers the advantage of being able to distribute the labor period by artificially adjusting the silk-collecting period. Furthermore, moth silk can be directly harvested from wild moths, eliminating the need for genetically modified silk production and maintenance, as is required for spider silk production.

[0021] The researchers discovered that composite materials reinforced with silk from the ground moth can achieve an elastic modulus more than 10 times higher than the polymer matrix alone. Furthermore, the use of long-fiber silk significantly improves the low elongation at break, a challenge faced by carbon fiber-reinforced plastics (CFRP) and glass fiber-reinforced plastics (GFRP).

[0022] The present invention provides the following inventions based on the above-mentioned research results.

[0023] (1) Reinforcing fibers for fiber-reinforced composite materials, including silk from the moth.

[0024] (2) A fiber-reinforced composite material comprising a polymer matrix and reinforcing fibers, wherein the reinforcing fibers comprise silk from the moth.

[0025] (3) The fiber-reinforced composite material according to (2), comprising silk threads of the moth containing short fibers having a length of 1 mm or more and less than 1 m.

[0026] (4) The fiber-reinforced composite material according to (3), comprising spun silk of the moth.

[0027] (5) The fiber-reinforced composite material according to (2) or (4), comprising silk threads composed of long fibers of 1 m or longer.

[0028] (6) The fiber-reinforced composite material according to any one of (2) to (5), further comprising organic fibers other than silk from the moth, inorganic fibers, or a combination thereof as reinforcing fibers.

[0029] (7) The fiber-reinforced composite material according to any one of (2) to (6), comprising silk threads of the moth arranged in one or more directions.

[0030] (8) The fiber-reinforced composite material according to (7), comprising a woven or knitted fabric composed entirely or partially of silk from the moth.

[0031] (9) The fiber-reinforced composite material according to any one of (2) to (8), wherein the polymer matrix is ​​a resin, glue, starch, agar, or a combination thereof.

[0032] (10) The fiber-reinforced composite material according to any one of (2) to (9), wherein the mass fraction of the silk from the moth moth in the fiber-reinforced composite material is 0.5% by mass to 50% by mass.

[0033] (11) A method for producing a fiber-reinforced composite material, comprising a contacting step of bringing reinforcing fibers into contact with a polymer matrix, wherein the reinforcing fibers comprise silk from a sedge moth.

[0034] (12) The manufacturing method according to (11) includes a molding step of molding the reinforcing fibers and / or the polymer matrix into a desired shape using a mold, and a curing step of promoting and / or completing the polymerization reaction of the polymer matrix.

[0035] (13) The manufacturing method according to (12), further comprising a demolding step of removing the completed fiber-reinforced composite material from the mold.

[0036] This specification incorporates the disclosure of Japanese Patent Application No. 2017-170648, which is the basis of priority for this application.

[0037] Effects of the Invention

[0038] The fiber-reinforced composite material of the present invention can provide a fiber-reinforced composite material having high strength, high elastic modulus, and "stretching" properties that conventional CFRP and GFRP do not have. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 : Graphs showing the relationship between BSF fiber content and elastic modulus or strength. (A) The relationship between BSF fiber content and incremental elastic modulus, and (B) the relationship between BSF fiber content and incremental strength are shown, respectively.

[0040] Figure 2 : Graphs showing the results of thermal decomposition evaluation tests of sedge moth silk. N2 flow shows the nitrogen-purified atmosphere, and Air flow shows the air atmosphere. DETAILED DESCRIPTION

[0041] 1. Reinforced fiber

[0042] 1-1. Overview

[0043] A first embodiment of the present invention is a reinforcing fiber. The reinforcing fiber of the present invention is a reinforcing fiber for fiber-reinforced composite materials, characterized by comprising silk from the moth. The reinforcing fiber of the present invention can impart high strength, high elastic modulus, and tensile properties to the fiber-reinforced composite material.

[0044] 1-2. Definition

[0045] Frequently used terms in this specification are defined as follows.

[0046] The so-called "fiber-reinforced composite material" refers to a material that is integrated into one body by combining two or more different raw materials, namely the reinforcing fibers and the base material, without fusing them together.

[0047] In this specification, "reinforcement fiber" refers to the fiber matrix in fiber-reinforced composite materials. While generally considered a reinforcing material that imparts strength to a fiber-reinforced composite material, in this specification, reinforcing fiber refers to a reinforcing material that imparts at least one of strength, elastic modulus, and elongation to the fiber-reinforced composite material.

[0048] In this specification, the term "parent material," also referred to as "matrix," refers to the supporting substrate in a fiber-reinforced composite material. The parent material is typically the component that imparts strength in a fiber-reinforced composite material. However, in the present specification, the reinforcing fibers not only serve as the reinforcing material themselves, but the parent material can also serve as a filler between the reinforcing fibers, imparting strength to the reinforcing fibers. In other words, in the fiber-reinforced composite material of the present invention, the constituent raw materials enhance each other's strengths and / or compensate for each other's weaknesses. This results in a fiber-reinforced composite material with novel properties not inherent in the original raw materials.

[0049] In this specification, the term "polymer matrix" refers to a base material composed of organic polymers and / or inorganic polymers.

[0050] "Silk" as used herein refers to protein-based silk spun by insect larvae and adults for purposes such as nest building, locomotion, anchoring, cocooning, and predation. The term "silk" as used herein includes single fibers, spun fibers, spun silk, and aggregated fibers.

[0051] As used herein, "single filament" refers to the smallest unit of silk (monofilament). It refers to the fiber components, such as fibroin protein, obtained by removing covering components, such as sericin protein, from the spun silk fibers (described later). In principle, single filaments do not exist naturally; they are obtained by scouring spun silk fibers.

[0052] The term "spun silk fibers" as used herein refers to silk spun by insects. For example, the spun silk fibers of the moth are composed of two single fibers bonded together by a covering component to form a double filament.

[0053] The term "spun silk" as used herein refers to spun silk obtained by spinning staple fibers described later.

[0054] The so-called "aggregated fibers" in this specification are fibers composed of multiple silk fiber bundles, also known as multifilaments. The aggregated fibers in this specification are composed of single fibers, spun fibers, spun silk, or combinations thereof. The aggregated fibers in this specification include fibers composed only of silk from the same biological species, such as moth silk, and also include mixed fibers composed of multiple silks from different sources, such as moth silk and silkworm silk. In addition, the fibers are not limited to biological species such as moth silk. In addition, aggregated fibers include not only twisted fibers but also untwisted fibers.

[0055] In addition, when "silk" is abbreviated in this specification, it means silk from the ground moth unless otherwise specified.

[0056] As mentioned above, "psychidae" refers to the larvae of moths belonging to the family Psychidae of the order Lepidoptera. Psychidae moths are found worldwide, and each larva (psychidae) spends its entire larval stage in a nest, woven from natural materials such as leaves and branches, using its own silk. This nest is a bag-like structure that can wrap around the entire body, taking various shapes, including spindles, cylinders, and cones. Psychidae moths typically lurk within this nest, often accompanying the nest when feeding and moving, and generally pupating within it.

[0057] The "silk of the moth" as used herein refers to the silk spun by the moth.

[0058] 1-3. Composition

[0059] The reinforcing fiber of the present invention comprises silk from the ground moth. The species of ground moth from which the ground moth silk used as the reinforcing fiber of the present invention is derived is not limited. For example, the ground moth 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. Species belonging to any genus may be used. Specific examples of ground moth species include Eumeta japonica, Eumeta minuscula, and Nipponopsyche fuscescens. In addition, regarding the age of the larvae (moth), all ages can be used as subjects. In addition, there is no restriction on gender. However, for the purpose of obtaining thicker and longer moth silk, large moths are preferred. For example, within the family of Mothidae, the larger the species, the more preferred. Therefore, from the perspective of obtaining longer and thicker moth silk, the large moth and the tea moth are preferred species as moths used in the present invention. Moreover, for larvae of the same species that are closer to the end of their instar, the more preferred, and even larger females are more preferred.

[0060] The silk produced by the moth moth consists of two types: scaffolding and nesting. The silk used as reinforcing fibers can be either or a mixture of both. Scaffolding is the silk produced by the moth before it moves, serving as a scaffold to prevent it from falling from branches and leaves during movement. Nesting is the silk that makes up the nest, produced to connect leaves and branches and to create a comfortable living environment within the nest. Scaffolding is generally thicker and mechanically stronger than nesting, making it more preferable as a reinforcing fiber.

[0061] The length of the silk of the moth used as the reinforcing fiber is not limited, and examples thereof include short fibers (short fiber yarns), long fibers (long fiber yarns), or combinations thereof.

[0062] As used herein, "short fibers" refer to fibers having a major axis length of 1.0 mm or greater and less than 1 m, 1.5 mm or greater and less than 80 cm, 2 mm or greater and less than 60 cm, 2.5 mm or greater and less than 50 cm, 3 mm or greater and less than 40 cm, 3.5 mm or greater and less than 30 cm, 4 mm or greater and less than 20 cm, 4.5 mm or greater and less than 10 cm, and 5.0 mm or greater and less than 5 cm. Examples include fragments of scaffolding yarn and nesting yarn. When using short fibers as reinforcing fibers, the short fibers may be used as spun silk, or may be dispersed in a fiber-reinforced composite material. A combination of these may also be used.

[0063] As used herein, "long fibers" refer to fibers having a 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, or 10 m or more. As long as the fiber length is greater than the above-mentioned length, the long fibers may be single fibers, filaments such as spinning fibers, pile fibers such as spun silk, or any combination thereof. There is no particular upper limit to the fiber length of the long fibers. For pile fibers, their length can be extended without restriction through spinning. On the other hand, for long fibers, the fiber length is equivalent to the length of the major axis of the silk that can be continuously spun by the moth. For example, it is 1.5 km or less, 1 km or less, 900 m or less, 800 m or less, 700 m or less, 600 m or less, 500 m or less, 400 m or less, 300 m or less, 200 m or less, or 100 m or less. However, due to the unique ecology of the moth, existing technology has so far prevented the production of filaments longer than 1 meter from moth silk. Silkworms spin cocoons by continuously spinning silk, so simply scouring the cocoons and reeling them can easily produce long, filamentous silk. However, moths pupate directly in their larval nests, unlike silkworms, which spin their cocoons before pupation. Furthermore, moth nests are typically expanded from the first instar as they grow, resulting in a mixture of new and old silk. Furthermore, at one end of the moth's nest's long axis, there's an opening that exposes a portion of the moth's head and thorax for movement and feeding, and at the other end, there's an excretion hole for excretion. These two holes typically cause the silk to become fragmented and discontinuous within the nest. As a result, moth nests are composed of relatively short strands of silk entwined together, making it impossible to produce long, filamentous silk from them using conventional methods. Although the scaffolding yarn of the moth is relatively continuous, it is spun in a zigzag pattern due to the footholds used for movement. Furthermore, the movement of the moth itself causes the yarn to become intricately entangled, making reeling difficult, even if it were possible. However, the inventors developed a method for arranging the moth along a linear path of a specific width, causing it to spin the scaffolding yarn substantially parallel to the path. This method has led to the stable mass production of long-fiber moth silk (Japanese Patent Application No. 2017-110003).

[0064] When using long filament yarn, the orientation of the moth silk is not limited. By arranging multiple fiber bundles composed of filaments and pile yarns in one direction or two or more directions, the moth silk can be made into a string, sheet, or three-dimensional structure.

[0065] As examples of arranging the fiber bundles of moth silk in one direction, there are cases where they are arranged in a straight line on a flat surface (UD material), and woven fabrics (knits) obtained by forming the moth silk fiber bundles into a continuous loop (course) while mooring them to the loops of adjacent fiber bundles, and tying the longitudinal loops (wale) to form a flat surface (sheet). The texture of the woven fabric itself has elasticity in its structure. However, carbon fiber and glass fiber, which were the main reinforcing fibers in the past, will break if bent into a loop, making it difficult to make woven fabrics. On the other hand, moth silk is easy to make woven fabrics due to the softness of the fiber. By using moth silk woven fabrics as reinforcing fibers, in addition to the "stretching" mechanical properties of the silk itself, the elasticity of the woven fabric is added, thereby obtaining excellent properties that previous reinforced fiber composite materials did not have.

[0066] As an example of arranging the fiber bundles of the moth silk in two directions, textiles such as woven fabrics and braided tapes (assemblies) can be cited. The so-called woven fabric is obtained by intersecting the longitudinal and transverse threads to form a plane (sheet). The woven fabric can be either a plain weave in which the longitudinal and transverse threads are orthogonal to each other, or a twill weave in which the longitudinal and transverse threads are obliquely intersected. The so-called braided tape is obtained by combining multiple fibers into a thin rope or ribbon shape, including braided rope (assembly), woven rope (woven rope), rolled strip (woven rope), etc. As a specific example, a braided rope is obtained by weaving multiple fibers into a cylindrical shape along a metal core (mandrel) to form a thin rope-like structure (braided rope).

[0067] Another example is a nonwoven fabric obtained by randomly arranging fiber bundles of silk moths in three or more directions to form a flat surface (sheet).

[0068] The reinforcing fibers of the present invention may be composed solely of silkworm silk, or may further include one or more different reinforcing fibers within the scope of not hindering the effects of the present invention. Other reinforcing fibers may include organic fibers or inorganic fibers other than silkworm silk. Organic fibers may include plant-based natural fibers such as cotton and hemp with cellulose as the main component, animal-based natural fibers such as silk obtained from insects such as silkworms or wild silkworms, which are larvae of moths of the Saturniidae family, and spider silk, as well as synthetic fibers such as polyaramids, polyamides (including nylon), polyesters, polyethylene, acrylic acid, and rayon. Inorganic fibers may 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 silkworm silk with other reinforcing fibers, a synergistic effect can be achieved between the reinforcing fibers. For example, carbon fibers as reinforcing fibers for CFRP and glass fibers as reinforcing fibers for GFRP are boasted to have extremely high strength and elastic modulus, but due to the lack of tensile properties, they have low toughness and are brittle. On the other hand, sedge moth silk also has high strength and elastic modulus, but not as high as carbon fiber or glass fiber. However, sedge moth silk possesses stretching properties that carbon fiber and glass fiber lack. Therefore, combining sedge moth silk with carbon fiber and / or glass fiber as reinforcing fibers can leverage the strengths of both while compensating for their shortcomings. By using reinforcing fibers combining sedge moth silk with carbon fiber and / or glass fiber, fiber-reinforced composite materials with extremely high strength and elastic modulus, as well as stretching properties, can be produced.

[0069] When the reinforcing fiber of the present invention contains other different reinforcing fibers in addition to the worm silk, the content of the worm silk in the reinforcing fiber when used in the fiber-reinforced composite material is not limited. It can be 1% or more, 3% or more, 5% or more, 8% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 92% or more, 95% or more, 97% or more, 98% or more, or 99% or more.

[0070] When the reinforcing fibers include other reinforcing fibers in addition to the sedge moth silk and long fibers are used as the other reinforcing fibers, the orientation of the other reinforcing fibers can be the same as that of the sedge moth silk in principle. Therefore, a detailed description thereof will be omitted.

[0071] 2Fiber-reinforced composites

[0072] 2-1. Overview

[0073] A second aspect of the present invention is a fiber-reinforced composite material. This fiber-reinforced composite material is characterized by using the reinforcing fiber for a fiber-reinforced composite material described in the first aspect, namely, a reinforcing fiber comprising silk from a sedge moth, as a fiber base material. This invention provides a fiber-reinforced composite material having high strength, a high elastic modulus, and tensile properties not found in conventional CFRP and GFRP.

[0074] 2-2. Structure

[0075] 2-2-1. Composition

[0076] The fiber-reinforced composite material of the present invention comprises a polymer matrix and reinforcing fibers comprising silk of the moth as essential components.

[0077] (Polymer Matrix)

[0078] A polymer matrix refers to a base material composed of organic polymers and / or inorganic polymers. The polymer matrix used in the fiber-reinforced composite material of the present invention is either an organic polymer or an inorganic polymer, or both. The organic polymers referred to herein include natural polymers and synthetic polymers.

[0079] Natural polymers are polymers that exist in nature, such as proteins, polysaccharides, and natural resins. Specific examples of proteins include glue (including collagen and gelatin). Specific examples of polysaccharides include starch, cellulose, mannan, agar, and the like. Specific examples of natural resins include lacquers, rosin, latex (natural rubber), and shellac.

[0080] Synthetic polymers are polymers obtained by linking monomers through polycondensation reactions or polyaddition reactions, and examples thereof include synthetic resins and synthetic rubbers.

[0081] Synthetic resins are also called plastics. The synthetic resin used as the polymer matrix in the fiber-reinforced composite material of the present invention can be any one of a thermosetting resin, a thermoplastic resin, or a combination thereof. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, vinyl ester resins, and phenolic resins. Examples of thermoplastic resins include polyethylene, polypropylene, polyester, polystyrene, polyvinyl chloride, methacrylic resins, fluororesins, polycarbonates, polyurethanes, aromatic polyetherketone resins, and polyphenylene sulfide resins.

[0082] Examples of the synthetic rubber include butadiene rubber, chloroprene rubber, styrene-butadiene rubber, isoprene rubber, ethylene-propylene rubber, nitrile rubber, silicone rubber, acrylic rubber, fluororubber, and urethane rubber.

[0083] (Reinforcement Fiber)

[0084] The reinforcing fibers used in the fiber-reinforced composite material of the present invention are reinforcing fibers comprising the reinforcing fibers described in the first embodiment, namely, silk from the moth moth. The specific structure of the reinforcing fibers has been described in detail in the first embodiment, and therefore will not be described here.

[0085] (Composition ratio)

[0086] The mixing ratio of the reinforcing fibers and the polymer matrix in the fiber-reinforced composite material of the present invention is not limited. Usually, the ratio is such that the polymer matrix as the base material can be imparted according to the high strength, high elastic modulus, stretching, etc., which are the characteristics of the target reinforcing fibers. In the fiber-reinforced composite material of the present invention, in addition to high strength and high elastic modulus, the mixing ratio is preferably such that the polymer matrix can be imparted with stretching that is the characteristic of the moth silk. Specifically, the mass fraction of the moth silk relative to the total dry mass of the fiber-reinforced composite material is 0.5% to 50% by mass, 0.8% to 40% by mass, 1% to 35% by mass, 1.5% to 30% by mass, 2% to 28% by mass, or 3% to 25% by mass.

[0087] 2-2-2. Structure

[0088] The structure of the fiber-reinforced composite material of the present invention, that is, the arrangement of the reinforcing fibers and the polymer matrix in the fiber-reinforced composite material, is not particularly limited. Examples include a state where short-fiber reinforcing fibers are dispersed within and / or on the surface of the polymer matrix, a state where a polymer matrix layer and a reinforcing fiber layer are laminated and integrated, a prepreg formed by impregnating a liquid polymer matrix with sheet-like reinforcing fibers, and a state where multiple prepregs are laminated with different reinforcing fiber orientations and integrated as a structure. Prepregs are intermediate materials in fiber-reinforced composite materials, but are also included in the fiber-reinforced composite material in this specification.

[0089] 2-3. Effect

[0090] The fiber-reinforced composite material of the present invention can provide a fiber-reinforced composite material that exhibits stretching properties not found in conventional fiber-reinforced composite materials such as CFRP and GFRP, by including silk from the moth as reinforcing fibers.

[0091] 2-4. Application

[0092] The fiber-reinforced composite material of the present invention can be utilized in a variety of fields, typified by conventional fiber-reinforced composite material applications. Examples include sports and leisure (golf clubs, rackets, fishing rods, automotive parts, etc.), residential (bathhouses, septic tanks, etc.), civil engineering (seismic reinforcement materials, lightweight building materials, wall and floor reinforcement materials, truss structural materials, etc.), transportation equipment (automobiles, ships, airplanes, helicopters, high-pressure hydrogen tanks, etc.), industrial machinery materials (housings, home appliance parts, printed circuit boards, wind turbine blades, etc.), and space-related applications (rocket, artificial satellites, etc.). In particular, the fiber-reinforced composite material of the present invention exhibits tensile properties not previously exhibited by conventional fiber-reinforced composite materials. Therefore, in addition to strength and elastic modulus, it is also suitable for use in applications requiring tensile strength.

[0093] Furthermore, when the reinforcing fibers are solely silk from the ground moth, or silk from the ground moth and other silks, and the polymer matrix is ​​a natural organic polymer such as collagen or gelatin, the resulting fiber-reinforced composite material has high biocompatibility. Therefore, it can also be used in the medical field as a matrix for tissue regeneration or vascular regeneration.

[0094] 3. Manufacturing methods of fiber-reinforced composite materials

[0095] 3-1. Overview

[0096] A third aspect of the present invention is a method for producing a fiber-reinforced composite material. This method is the method for producing and / or molding the fiber-reinforced composite material described in the second aspect. The production method of the present invention enables easy production and molding of fiber-reinforced composite materials containing silk from the moth.

[0097] 3-2. Methods

[0098] The method for producing a fiber-reinforced composite material according to the present invention is based on conventional methods for producing fiber-reinforced composite materials, except that filaments of the worm moth are used as the reinforcing fibers. For example, when long-fiber filaments of the worm moth are used as the reinforcing fibers, the production methods typically used for CFRP and GFRP can be directly applied. Various production methods are known, and an appropriate method can be selected based on the intended use, shape, and other factors.

[0099] For example, a prepreg can be made by impregnating a suitable polymer matrix into a woven, braided, or non-woven fabric containing reinforcing fibers made of silkworm moth silk. If the polymer matrix is ​​a thermosetting resin, the resulting prepreg is a semi-cured prepreg in which polymerization is not yet complete. On the other hand, if the polymer matrix is ​​a natural polymer such as a thermoplastic resin or collagen, the resulting prepreg is a cured prepreg in which polymerization is complete.

[0100] In addition, as the main molding methods, there are filament winding molding method, sheet winding molding method, press molding method, autoclave molding method, RTM (resin transfer molding) molding method, VaRTM (vacuum resin transfer molding) molding method, SMC (sheet molding compound) molding method, vacuum bag molding method, hand lay-up molding method, and fiber placement molding method.

[0101] The "filament winding method" is a method for forming tubular products by preparing one to several dozen filament bundles (bundles of 1,000 to tens of thousands of filaments), impregnating them with a polymer matrix, and winding them around a rotating mold (mandrel) to remove the core after curing. The "sheet winding method" has the same basic process as the filament winding method, but is a molding method in which a prepreg is wound around a mandrel instead of a filament bundle, and is removed after curing. The "pressing method" is a method in which a compound and a prepreg are placed in a mold and pressurized and heated to form the prepreg. The "autoclave molding method" is a method in which the prepregs are stacked in a mold, covered with a bag, and vacuum removed from the air and volatile substances in the autoclave, and then pressurized and heated to form the prepregs. The "RTM molding method," also known as the resin injection molding method, is a method in which a molten thermosetting resin is introduced under low pressure into a closed system of a preform with reinforcing fibers arranged in a mold, and then heated and cured to remove the prepregs. "VaRTM molding method" is a type of RTM method, which is a method of vacuuming a closed system stacked with reinforcing fibers, introducing a thermosetting resin, and then heating and curing to release the mold. "SMC molding method" is a method of stacking sheet materials composed of reinforcing fibers and a polymer matrix. "Vacuum bag molding method" is a method of vacuuming a stack sealed with a sealed film and compression molding it by atmospheric pressure. "Hand lay-up molding method" is a method of manually stacking prepregs in a molding mold and curing them. In addition, "fiber placement molding method" is a method of stacking prepregs processed into strips and filament bundles impregnated with a polymer matrix in various three-dimensional molds and curing them. The specific methods of these molding methods are all well-known methods in the field of fiber-reinforced composite materials and can be used as reference.

[0102] When using short-fiber silk from the moth moth as the reinforcing fiber, the basic operation can be carried out in the same manner as conventional methods for producing fiber-reinforced composite materials. For example, a method can be used in which the short-fiber silk from the moth moth is dispersed in a molten polymer matrix, the two are brought into contact, and the mixture is introduced into a desired mold for solidification and molding. Alternatively, a method can be used in which short-fiber reinforcing fibers are dispersed on the surface of a polymer matrix and then integrated by heat and pressure to produce a structure consisting of a polymer matrix layer and a reinforcing fiber layer.

[0103] 3-3. Manufacturing process

[0104] The production process of the fiber-reinforced composite material production method of the present invention includes a contacting step as an essential step, and optionally includes a molding step, a curing step, and a demolding step.

[0105] (1) Contact process

[0106] The so-called "contact step" is the process of bringing the reinforcing fibers into contact with the polymer matrix. The contact method is not particularly limited as long as the two components can be in direct contact. The reinforcing fibers can be dispersed, immersed, or impregnated in a dissolved liquid polymer matrix. Alternatively, as in the SMC molding method, bundles or sheets of reinforcing fibers can be sandwiched between sheets of polymer matrix.

[0107] The prepreg is formed by impregnating a sheet composed of reinforcing fibers with a polymer matrix, and its production process consists only of a contact step.

[0108] (2) Molding process

[0109] The "molding step" is a step of molding the reinforcing fibers and / or polymer matrix, which are components of the fiber-reinforced composite material, into a desired shape. This step is optional and is performed according to various production methods.

[0110] In this process, a mold such as a metal mold is used to form the part in a manner that matches the mold. Reinforcement fibers and prepregs can also be stacked and formed as needed. The order of the forming process and the aforementioned contact process varies depending on the manufacturing method and is not limited. For example, the aforementioned filament winding molding method, sheet winding molding method, compression molding method, autoclave molding method, hand lay-up molding method, fiber placement molding method, etc., perform the forming process after the contact process. On the other hand, RTM molding method and VaRTM molding method, because the preform of the reinforcing fibers is molded using a metal mold and the polymer matrix is ​​introduced into the mold, perform the contact process after the forming process. This can be performed according to the respective manufacturing methods.

[0111] (3) Curing process

[0112] The "curing step" refers to the process that accelerates and / or completes the polymerization reaction of the polymer matrix after the above steps. This step solidifies the polymer matrix, completing the fiber-reinforced composite material. The curing step may include a heating step and / or a cooling step.

[0113] The "heating step" is a step of accelerating and / or completing the polymerization reaction by heating the polymer matrix. This step is performed when a thermosetting resin is used as the polymer matrix. On the other hand, when the polymer matrix is ​​a thermoplastic resin or a natural polymer, since heating cancels the polymerization reaction and causes the polymer to soften or dissolve, this step can be equivalent to the contacting step or molding step described above.

[0114] The heating temperature is not particularly limited. Depending on the type of the polymer matrix used, it can usually be carried out in 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. In addition, 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. Usually, it can be carried out in the range of 0.5 hour 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.

[0115] The "cooling step" is a step of cooling the heated polymer matrix or solidifying it by cooling. When a thermosetting resin is used as the polymer matrix, this step is performed when the fiber-reinforced composite material, after the heat curing reaction has completed in the heating step, is cooled. Alternatively, when a thermoplastic resin or natural polymer is used as the polymer matrix, cooling accelerates and / or completes the polymerization reaction, and the fiber-reinforced composite material is completed by solidifying the polymer matrix.

[0116] The cooling temperature is also not limited. Different according to the type of the polymer matrix used, usually can be below 260 ℃, below 200 ℃, below 180 ℃, below 150 ℃, below 120 ℃, below 100 ℃, below 90 ℃, below 80 ℃, below 70 ℃, below 60 ℃, below 50 ℃, below 40 ℃, below 35 ℃, below 30 ℃, below 27 ℃, below 25 ℃, below 23 ℃, below 20 ℃, below 18 ℃, below 15 ℃, or below 10 ℃. The lower limit temperature is not particularly limited, usually can be 4 ℃, 0 ℃, -10 ℃, -15 ℃, or about -20 ℃. In addition, the cooling time can be carried out in the scope of 0.1 hour to 1 hour, 0.2 hour to 0.9 hour, 0.3 hour to 0.8 hour, 0.4 hour to 0.7 hour, or 0.5 hour to 0.6 hour.

[0117] (4) Demolding process

[0118] The demolding step is the process of removing the fiber-reinforced composite material from the mold after the curing step. Specifically, this step involves removing the completed fiber-reinforced composite material from the mold or mandrel used in the molding step. Demolding methods known in the art can be used.

[0119] Example

[0120] <Example 1: Production of fiber-reinforced composite material using silk from the moth as reinforcing fiber (1)>

[0121] (Purpose)

[0122] To prepare fiber-reinforced composite materials containing silk from the ground moth as reinforcing fibers, and to verify their physical properties.

[0123] (method)

[0124] The reinforcing fibers use long fiber bundles of silk from the moth, and the polymer matrix uses ethylene-vinylacetate copolymer (EVA) resin.

[0125] Long fiber bundles of moth silk were prepared according to the method described in the specification of Japanese Patent Application No. 2017-110003. The moths used were final-instar larvae of the giant moth, collected from orchards in Tsukuba City, Ibaraki Prefecture. A nearly square metal can described in Example 1 of the specification of Japanese Patent Application No. 2017-110003 was used as a long fiber production device for moth silk. Above a plate-like member corresponding to the side of the metal can, a closed-loop linear path with a width of 1.7 mm and a circumference of 1.1 m was placed, with the linear road surface facing upward. Moths were placed on this linear path, and after confirming that the moths were spinning silk on the linear path while rotating around it, the path was left at room temperature. After two days, the moths were recovered from the apparatus, and the moth silk strands stacked on the linear path were stripped off using a stripper. The resulting approximately 150 m of moth silk strands were bundled into a 1.1 m circumference, forming a long fiber bundle consisting of at least 150 individual fibers. This long fiber bundle was then scoured for two minutes in a 0.05 mol / L boiling sodium carbonate solution. After washing with pure water and air-drying, the resulting fiber bundle was used as a reinforcing fiber.

[0126] EVA resin was bonded using a hot air gun adhesive (Taiyo Electric Industry Co., Ltd.). As an alternative to a mold, a 35mm long and 10mm wide template made of a 0.5mm thick silicone rubber sheet was prepared. EVA resin was placed within the template and then pressed under 1-2 MPa to produce two EVA resin sheets. Next, a bundle of prepared bagworm silk fibers (BSF) or carbon fiber (CF) as a control was sandwiched between the EVA resin sheets as reinforcing fibers. The sheets were then pressed under 1-2 MPa using two hot plates heated to 100°C. After cooling, a fiber-reinforced composite material consisting of bagworm silk fibers (BSF) and EVA resin (BSF / EVA composite) and a fiber-reinforced composite material consisting of carbon fiber (CF) and EVA resin (CF / EVA composite) were obtained. Simultaneously, as a negative control, a single EVA resin sheet was produced by pressing two sheets together without reinforcing fibers.

[0127] The obtained sheet was cut into test pieces along the reinforcing fibers and subjected to the mechanical test described below. The mass fraction of the reinforcing fibers relative to the total mass of the test piece was calculated as the fiber content (mass %: wt %).

[0128] (result)

[0129] The mechanical test results (n=3) of the BSF / EVA composite material and the EVA resin are shown in Table 1.

[0130] Table 1

[0131]

[0132] In Table 1, "elastic modulus" means the initial elastic modulus. This is equivalent to the proportional constant in the deformation region that satisfies the relationship in which the force is proportional to the deformation amount, that is, Hooke's law, when the sample is stretched, and is given as the slope of the initial slope of the stress-strain curve. Generally, the larger the value, the smaller the deformation relative to the tensile stress, and the harder the property. In addition, "maximum strength" refers to the maximum stress before it breaks. Generally, the larger the value, the stronger the stress it can withstand. And, "strain" refers to the elongation at break, which refers to the stretching of the sample until it breaks. Generally, the larger the value, the better the elongation. "Incremental elastic modulus" and "incremental strength" represent the difference between the elastic modulus and the maximum strength in the resin alone and the fiber composite.

[0133] The elastic modulus and maximum strength of the BSF / EVA composite material were significantly increased compared to those of the EVA resin alone. This suggests that the BSF / EVA composite material is harder and stronger than the EVA resin alone. In addition, the incremental elastic modulus (A) and incremental strength (B) are plotted against the fiber content, as shown in the figure. Figure 1 As shown in the figure, it can be confirmed that the fiber content increases linearly with high correlation in each case. From these results, it can be confirmed that the use of silk from the moth as a reinforcing fiber can impart hardness (high elastic modulus) and strength (high strength) to the EVA resin.

[0134] Furthermore, the strain (elongation at break) of the BSF / EVA composite material was measured three times, and all values ​​exceeded 30% (Table 1). These results suggest that using silk from the moth as the reinforcing fiber in fiber-reinforced composites can significantly improve the low elongation at break, a problem with conventional carbon fibers and glass fibers.

[0135] From the above results, it is clear that the silk of the moth can effectively improve the mechanical properties of the polymer matrix, such as strength, elastic modulus, and elongation at break, with a fiber content of only about 2wt%. In addition, by changing its fiber content, the contribution to the mechanical properties can be controlled.

[0136] <Example 2: Production of fiber-reinforced composite material using silk from the moth as reinforcing fiber (2)>

[0137] (Purpose)

[0138] A fiber-reinforced composite material was prepared using silk from the moth as the reinforcing fiber and a polymer matrix different from that in Example 1, and its physical properties were verified.

[0139] (method)

[0140] The EVA resin used in Example 1 is a soft resin capable of stretching several times. Therefore, in this example, a fiber-reinforced composite material (BSF / PS composite material) was prepared using polystyrene resin (PS resin) (Eiken Chemical Co., Ltd.), a hard resin with lower elongation than EVA resin and a break elongation of only approximately 5%, as the polymer matrix. The mechanical properties of the composite material were verified using the same methods as in Example 1.

[0141] The basic conditions were the same as those of Example 1. However, the pressure pressing conditions were 10 MPa to 12 MPa at 150°C.

[0142] (result)

[0143] Table 2 shows the mechanical test results of the BSF / PS composite material and the PS resin alone.

[0144] Table 2

[0145]

[0146] Table 2 shows that the strain (elongation at break), which is only 5.2% in the PS resin alone, is increased to 33.8% in the BSF / PS composite material containing fiber bundles of sedge moth silk. This result demonstrates that even a rigid resin matrix, such as the polymer matrix used in the fiber-reinforced composite, which exhibits a lower elongation at break than sedge moth silk, can impart the high elongation characteristic of sedge moth silk.

[0147] <Example 3: Production of a fiber-reinforced composite material using short fibers of sedge moth silk as reinforcing fibers>

[0148] (Purpose)

[0149] To verify the physical properties of fiber-reinforced composite materials using short fibers of silk from the moth as reinforcing fibers.

[0150] (method)

[0151] Short fibers of silk from the moth were used as reinforcing fibers, and polyvinyl alcohol (PVA) (Woehler Chemical) was used as the polymer matrix.

[0152] Single fibers of sedge moth silk were cut into approximately 5 mm long fibers. The fibers were then dispersed in a PVA aqueous solution and formed onto a glass slide to produce a BSF / PVA composite film. The fiber content is the mass fraction of sedge moth silk staple fibers relative to the total dry weight of the film. The film was then cut into elongated test pieces for subsequent mechanical testing.

[0153] (result)

[0154] The elastic modulus of a BSF / PVA composite with a fiber content of 3.74 wt% was 184.1 MPa, a more than 10-fold improvement compared to PVA resin alone (14.1 MPa). This result suggests that even short-fiber silk can impart a very high elastic modulus to fiber-reinforced composites.

[0155] <Example 4: Thermal Decomposition Evaluation Test of Corydalis moth Silk>

[0156] (Purpose)

[0157] The manufacture of fiber-reinforced composite materials may include a heat treatment to depolymerize or promote polymerization of the polymer matrix. For example, if the polymer matrix is ​​a thermoplastic resin, heating depolymerizes the resin, causing it to soften or dissolve. Conversely, in the case of a thermosetting resin, heating promotes polymerization, causing it to solidify. In either case, during the manufacture of fiber-reinforced composite materials, the reinforcing fibers are exposed to high temperatures along with the polymer matrix. Because sedge moth silk is a protein, heating above its temperature tolerance could result in modification or decomposition of the fibers themselves, thus defeating the purpose of the invention. Therefore, the heat tolerance temperature of sedge moth silk was investigated.

[0158] (method)

[0159] Silk from the moth was treated at temperatures ranging from 130°C to 300°C for 1 hour, and the mass loss (%) due to thermal decomposition was evaluated by thermogravimetric analysis (TGA). The experiments were conducted under nitrogen flow and air flow.

[0160] (result)

[0161] The results are shown in Figure 2 Even when treated at 260°C for one hour in a nitrogen-purged atmosphere, the mass loss due to heat was less than 10%. This suggests that if the silk is heated below 260°C, the effects of thermal decomposition are almost negligible, and that the reinforced fiber composite material of the present invention can be produced even when heated to 260°C.

[0162] All publications, patents, and patent applications cited in this specification are hereby incorporated herein by reference.

Claims

1. A method for producing a fiber-reinforced composite material, wherein: The fiber-reinforced composite material includes a polymer matrix and reinforcing fibers, wherein the reinforcing fibers are silk threads of the moth having a length of 1 m or more and arranged in one or more directions.

2. The method for producing a fiber-reinforced composite material according to claim 1, wherein: The fiber-reinforced composite material further comprises organic fibers other than the silk of the moth, inorganic fibers, or a combination thereof.

3. The method for producing a fiber-reinforced composite material according to claim 1 or 2, wherein: The fiber-reinforced composite material comprises a woven or knitted fabric entirely or partially composed of silk from the moth.

4. The method for producing a fiber-reinforced composite material according to claim 1, wherein: The polymer matrix is ​​glue, starch, agar, or a combination thereof.

5. The method for producing a fiber-reinforced composite material according to claim 1, wherein: The polymer matrix is ​​resin, starch, agar, or a combination thereof.

6. The method for producing a fiber-reinforced composite material according to claim 1, wherein: The mass fraction of the silk from the moth is 0.5% to 50% by mass in the fiber-reinforced composite material.

Images