JP2010024413A - Fiber-reinforced composite material and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber-reinforced composite material excellent in both fatigue and impact characteristics at low cost. <P>SOLUTION: This fiber-reinforced composite material in which a polymer-based matrix is reinforced by a fibrous reinforcing material is produced by impregnating the fibrous reinforcing material with a material made by dispersing microfibrillated cellulose in the polymer-based matrix, and solidifying the resultant material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fiber reinforced composite material in which a polymer base material is reinforced with a fibrous reinforcing material and a method for producing the same.

  Since this type of composite material has excellent mechanical properties such as high specific strength and specific rigidity, its use as a structural material in various industrial fields has been studied or actually used.

  On the other hand, for example, in the above-mentioned composite material using long fibers as a fibrous reinforcing material, micro cracks tend to occur in a narrow base material region between fibers relatively quickly under repeated load. This type of crack can grow and cause fatigue failure. Microcracks generated in a relatively brittle polymer base material tend to easily develop even under the action of an impact load, and the energy absorption capacity of the base material is low. Further, when the fibrous reinforcing material is supplied to the base material in the form of a sheet, the composite material has a laminated structure, and therefore, it is easy to cause delamination against impact.

For example, in Patent Document 1 and Patent Document 2 below, for the purpose of improving impact resistance, a resin composition using carbon fiber as a reinforcing material and an epoxy resin as a base material, the carbon nanotube ( CNT) and nano-sized fine carbon fibers (CNF) as a filler are disclosed.
JP 2003-12939 A JP 2004-3000221 A

  However, any of the fillers disclosed in the above patent documents has poor interfacial adhesion with the base material. For this reason, the characteristics of micron-order or sub-micron-order fine fibers cannot be fully utilized, and the effect of suppressing the generation and propagation of cracks is small. In addition, since the specific gravity of the filler is usually larger than that of a base material such as a synthetic resin, even if the fiber is supplied into the base material, precipitation occurs and it is difficult to uniformly disperse the filler. . In this case, when the resin composition is impregnated, the filler is not included in the resin that has entered the narrow region between the fibers, and the occurrence and progress of microcracks that directly affect fatigue characteristics and impact characteristics are suppressed. Difficult to do. In addition, since all the fillers are expensive, they are unsuitable for manufacturing mass-produced products using the composite material.

  In addition, the above problem is not limited to long fibers, but can occur similarly when short fibers are used as reinforcing materials. That is, in a composite material using short fibers as a reinforcing material, the fiber ends of the fibers are likely to be the starting point of crack generation / development, and this tendency becomes more prominent in fatigue fracture and impact fracture. Therefore, improvement in fatigue characteristics and impact characteristics is also demanded in composite materials using short fibers as reinforcing materials.

  In view of the above circumstances, an object of the present invention is to provide a low-cost fiber-reinforced composite material excellent in both fatigue characteristics and impact characteristics.

The solution to the above problem is achieved by the fiber-reinforced composite material according to the present invention. That is, this composite material is a fiber reinforced composite material obtained by reinforcing a polymer base material with a fibrous reinforcement, and is further characterized by the fact that microfibril cellulose is dispersed in the polymer base material.

  Microfibril cellulose is fibrillated mainly by applying mechanical shearing force to cellulose constituting natural plant matter, and is a fine fiber having a submicron scale (0.01 to 0.1 μm order) fiber diameter. In addition, the specific gravity of microfibril cellulose is smaller than that of the carbon-based filler and close to the specific gravity of the polymer base material. From the above, it is possible to supply the base material to the fibrous reinforcing material in a state of being uniformly dispersed in the polymer base material without precipitating the microfibril cellulose, and the microfibril dispersed in the base material. Cellulose can enter a narrow matrix region between fibrous reinforcements or between layers. Thereby, for example, in a composite material using long fibers as a fibrous reinforcing material, it is possible to suppress the occurrence of microcracks in the base material region. Moreover, the growth of the microcrack once generated can be suppressed by the bridging action of the fine fibers. Also, in composite materials with short fibers as reinforcing materials, the stress generated at the fiber ends is shared by microfibril cellulose, so that microcracks are generated and propagated under repeated and impact loads compared to conventional materials. Is suppressed. In addition, since the said fine fiber has cellulose as a main component, compared with the above-mentioned carbon-type filler, adhesiveness with a polymeric base material is also favorable. Further, since the fibers are very fine as described above, the specific surface area is large and the bonding area with the base material is also large. From the above points, the composite material according to the present invention can suppress the occurrence and progress of microcracks by making full use of the characteristics of microfibrils dispersed in the base material as fine fibers. It is possible to improve the characteristics and impact characteristics. Further, since the filler is obtained by subjecting cellulose to mechanical processing, it can be obtained at a very low cost. Therefore, the production cost of the composite material according to the above configuration can be kept low and the mass productivity can be increased.

  Here, any fibrous reinforcing material can be used as the fibrous reinforcing material as long as it functions as a reinforcing material for the polymer base material. The material (different from organic, inorganic, natural, synthetic, etc.), fiber diameter (at least orders higher than microfibril cellulose), or its supply form (unidirectional, plain weave, non-woven fabric, etc.) are particularly limited Not. Although the fiber length is not particularly limited, it shows a very excellent fatigue property / impact property improvement effect when the long fiber is used as a reinforcing material from the above-described crack initiation / suppression mechanism and the experimental results described later. On the other hand, when paying attention to Young's modulus, a fibrous reinforcing material exhibiting a Young's modulus that is at least equal to or higher than that of microfibril cellulose is suitable, and an example thereof is carbon fiber.

  In addition, any high molecular weight base material can be used regardless of its kind. Here, in the case where importance is attached to the adhesiveness with the above-described microfibril cellulose, a resin having a hydroxyl group is suitable. This is because hydrogen bonds can be expressed with microfibril cellulose and high adhesive strength can be imparted between them. Among the resins having a hydroxyl group, an epoxy resin excellent in mechanical properties is preferable.

  The weight ratio of the microfibril cellulose to the polymer base material is preferably 0.01 wt% or more and 2.0 wt% or less, and more preferably 0.1 wt% or more and 1.0 wt%. In order to obtain the effect of improving the above-described fatigue characteristics / impact characteristics, at least 0.01 wt% of microfibril cellulose is necessary, and if it exceeds 2.0 wt%, the dispersibility in the polymer base material is increased. It is because it will fall extremely.

The composite material may be a prepreg formed by semi-curing a polymer base material. As described above, since the composite material according to the present invention can improve fatigue characteristics or impact characteristics at a relatively low cost, an industrial product using the composite material can be obtained by prepregizing the composite material. Mass production at low cost is possible.

  The composite material is suitably applied to, for example, sports equipment, in addition to being suitably applied to, for example, the vehicle, ship, and aviation fields because of its excellent mechanical properties and light weight. In particular, since the composite material according to the present invention is excellent in fatigue characteristics and impact characteristics, it can be suitably applied to, for example, sporting equipment such as tennis rackets, golf club shafts, baseball bats and other ball game equipment having a hitting portion. It is.

  The solution to the above problem is a method of obtaining a fiber reinforced composite material in which a polymer base material is reinforced with a fibrous reinforcing material by supplying a polymer base material to the fibrous reinforcing material and solidifying it. In addition, it can also be achieved by a method for producing a fiber-reinforced composite material, characterized in that a polymer base material in which microfibril cellulose is dispersed is supplied to a fibrous reinforcing material.

  Further, when the microfibril cellulose is supplied in a state containing moisture, the microfibril cellulose is substituted with a solvent such as alcohol, and the microfibril cellulose after the substitution is put into the polymer base material. You may make it disperse | distribute. Dispersibility of microfibril cellulose in the base material is important for obtaining the above-described effects of improving fatigue characteristics and impact characteristics. When the cellulose is dried to remove moisture contained in the microfibril cellulose, the cellulose Are entangled with each other and easily become a lump. On the other hand, according to the above-described method, the solvent-containing microfibril cellulose can be mixed with the polymer base material while maintaining a low viscosity, and the polymer system can be obtained without agglomerating the microfibril cellulose. A state of being uniformly dispersed in the base material can be easily realized. Therefore, a composite material product in which microfibril cellulose is uniformly dispersed in the base material can be obtained by supplying the base material in this state to the fibrous reinforcing material and solidifying it.

  Of course, the method of dispersing the microfibril cellulose is not limited to the above, and other methods can be adopted. For example, freeze-drying treatment may be applied to microfibril cellulose containing water to remove the water in the microfibril cellulose. According to this method, moisture is removed by sublimation in a reduced pressure environment, so that shrinkage such as normal drying hardly occurs. Therefore, cotton-like microfibril cellulose that leaves many spaces inside can be obtained. In such a state, the dispersibility in the base material is also good. Further, in this method, since the microfibril cellulose is dispersed in the base material as in the case of the solvent substitution described above, an operation for positively removing the solvent is not particularly required. Good. Alternatively, as still another means, for example, a method of removing moisture in the microfibril cellulose by a spray drying method can be adopted. The spray-drying method is generally a method for separating and extracting a powdery object or a granular object in a fluid. However, if the object is a fine object such as microfibryl cellulose, the above-described method may be used. By the method, dry microfibril cellulose can be obtained.

  As described above, according to the present invention, a fiber-reinforced composite material excellent in both fatigue characteristics and impact characteristics can be provided at low cost.

The fibrous reinforcing material constituting the composite material according to the present invention is arbitrary as long as it functions as a reinforcing material for the polymer base material, such as carbon fiber (PAN type, pitch type, etc.), glass fiber, ceramic fiber, Aramid fibers, or synthetic resin fibers such as polyethylene fibers, polyarylate fibers, and PBO fibers (polylube paraphenylene benzoxazole) can be used regardless of whether they are organic or inorganic. Of course, natural fibers (including naturally derived fibers) such as plant fibers (bamboo fibers, hemp fibers, etc.) and animal fibers (wool, etc.) can also be used. Further, the supply form to the base material is also arbitrary, and it is possible to supply the base material (impregnated with the base material) in the form of a fiber bundle or in the form of a sheet-like woven fabric with the fiber bundle as a unit. is there. Specifically, unidirectional fibrous forms (including forms such as yarns and cross plies), woven forms (such as plain weaves), non-woven forms, and mat forms (such as chopped strand mats) are examples of supply forms.

  The polymer base material is not particularly limited, and for example, thermosetting resins such as unsaturated polyester, epoxy resin, polyamide resin, and phenol resin can be used. It is also possible to use a thermoplastic resin such as methyl methacrylate. In addition, when a resin having a hydroxyl group is used with an emphasis on adhesiveness with microfibril cellulose, an epoxy resin excellent in mechanical properties can be suitably used.

  Various types of epoxy resins can be used regardless of whether they are one-pack type or two-pack type. Usable epoxy resins also include various modified epoxies such as vinyl ester, such as rubber fine particles such as ATBN and CTBN, and epoxy resins modified with thermoplastic fine particles (such as nylon). In this case, a fiber-reinforced composite material in which rubber fine particles are dispersed in addition to microfibril cellulose is formed in the epoxy resin as the polymer base material.

  As the microfibril cellulose, those obtained by converting the plant material into microfibrils as described above or those derived from bacteria (produced by bacteria) can be used. Here, when producing from plant matter, various plant matter can be used regardless of whether natural or artificial, and specific examples include wood fiber, bast fiber (bamboo fiber, etc.), leaf stem fiber (jute, Natural fibers related to each part, such as kenaf) and seed hair (cotton, etc.), can be mentioned as raw materials. Of course, it is also possible to extract these from pulped ones. Among these, so-called thick wall fibers extracted from thick wall cells such as bamboo vascular sheaths and woody parts of trees such as cedar are excellent in aspect ratio. Depending on the degree of fibrillation of these raw materials, microfibril cellulose having a fine network structure (in other words, a spider web-like fine network structure) can be obtained, and this can also be used.

  As a preferred example of the combination of the constituent elements exemplified above, for example, a plain sheet-like long fiber carbon fiber is used as a reinforcing material, an epoxy resin is used as a polymer base material, and a microfibril cellulose is used as a filler. Examples thereof include carbon fiber reinforced plastic (CFRP) obtained by impregnating a carbon fiber with an epoxy resin in which microfibril cellulose is dispersed and curing the resin. Hereinafter, an example of a method for producing the CFRP will be described.

  The composite material (CFRP) includes a step (A) of performing alcohol substitution on water-containing microfibril cellulose, a step (B) of dispersing the microfibril cellulose after alcohol substitution in an epoxy resin, and the cellulose It is manufactured through the step (C) of impregnating the dispersed epoxy resin into a sheet-like carbon fiber and molding it into a predetermined shape. Details of each step will be described below.

(A) Alcohol substitution process First, microfibril cellulose is prepared. The microfibril cellulose prepared here is obtained, for example, by fibrillating a pulp-like natural fiber as a raw material with a high-pressure homogenizer or the like. Therefore, the microfibril cellulose obtained as described above contains a very large amount (about 90 wt%) of water. Therefore, the cellulose is subjected to an alcohol substitution treatment to remove moisture contained in the microfibril cellulose. As an example of a specific method, first, microfibril cellulose and an alcohol solution in the same amount as the water contained in the cellulose are mixed and stirred, and then the mixed stirring solution is vacuum filtered to remove moisture. I do. Then, an appropriate amount of an alcohol liquid is further supplied to the sheet-like microfibril cellulose obtained by this operation, and the sheet-like microfibril cellulose is loosened with an ultrasonic homogenizer and dispersed uniformly in the alcohol liquid. Although the case where alcohol is used as a substitution medium is illustrated here, of course, the substitution treatment can also be performed using a solvent other than alcohol.

(B) Dispersing step After supplying the microfibril cellulose obtained in the above step (A) to the epoxy resin and stirring sufficiently, the alcohol liquid is evaporated by heating to a predetermined temperature (about 90 ° C) in a vacuum furnace. Let Thereby, an epoxy resin (resin composition) in a state where microfibril cellulose is uniformly dispersed is obtained. Under the present circumstances, the supply ratio of the microfibril cellulose with respect to an epoxy resin is adjusted between 0.1 wt% and 0.5 wt%, for example. In order to facilitate the dispersion of microfibril cellulose, an epoxy resin that has been heated to a predetermined temperature in advance may be used.

(C) Molding step A carbon fiber reinforced plastic is molded by, for example, a hand lay-up method with the resin composition and sheet-like carbon fiber obtained as described above. That is, the sheet-like carbon fiber is laminated while the sheet-like carbon fiber is impregnated with the resin composition. And by pressing this while heating, a carbon fiber reinforced plastic plate having a predetermined thickness is obtained. In addition, it is also possible to perform the alcohol removal process performed by the said dispersion | distribution process (B) after lamination | stacking.

  In addition, although the case where the alcohol substitution method was used regarding the removal of the water | moisture content contained in microfibril cellulose was demonstrated in the said exemplary manufacturing method, of course, methods other than this can also be taken. For example, it is also possible to remove moisture in microfibril cellulose by freeze drying treatment instead of alcohol substitution. In this case, the composite material (CFRP) includes a step (A ′) of subjecting the microfibril cellulose containing moisture to freeze drying, and a step (B ′) of dispersing the microfibril cellulose after freeze drying in the epoxy resin. And a step (C) of impregnating a sheet-like carbon fiber with a dispersed epoxy resin and forming it into a predetermined shape. In addition, since the microfibril cellulose after the drying treatment by the freeze drying method is very easy to absorb moisture, the series of steps from the drying treatment step (A ′) to the resin dispersion step (B) is performed in an absolutely dry environment. Or by impregnating the microfibril cellulose after the drying treatment step (A ′) with a suitable solvent (preferably a volatile solvent such as alcohol) and dispersing the impregnated body in the epoxy resin. It is also possible.

  Moreover, it is also possible to remove the water in the microfibril cellulose by spray drying treatment instead of the solvent replacement method or freeze drying method. In this case, the composite material (CFRP) includes a step (A ″) of subjecting the microfibril cellulose containing water to spray drying treatment, and a step of dispersing the microfibril cellulose after the spray drying treatment in the epoxy resin (B ″). And a step (C) of impregnating a sheet-like carbon fiber with a dispersed epoxy resin and forming it into a predetermined shape.

  Hereinafter, the results of experiments conducted by the present inventors in order to prove the usefulness of the present invention will be described.

(1) Specimen Here, first, a specimen commonly used in the following experiments (static tensile test, tensile tensile fatigue test, punching impact test, interlaminar fracture toughness test) will be described. Regarding materials, PYROF manufactured by Mitsubishi Rayon Co., Ltd. is used as a plain weave PAN-based carbon fiber.
IL (registered trademark) TR3110M was used as a unidirectional (UD) carbon fiber, and PYROFIL TR50S12L also manufactured by Mitsubishi Rayon Co., Ltd. was used. The polymer base material is jER (registered trademark) 828 manufactured by Japan Epoxy Resin Co., Ltd. as the main epoxy resin, and jER Cure (registered trademark) 113 manufactured by Japan Epoxy Resin Co., Ltd. as the curing agent. Each was used. Further, for microfibril cellulose (hereinafter referred to as MFC) as a filler, Selish (registered trademark) KY-100G manufactured by Daicel Chemical Industries, Ltd. was used.

  Here, three types of test pieces were prepared by blending 0.0 wt% (conventional product), 0.1 wt%, and 0.3 wt% (both products of the present invention) of MFC with the main material (epoxy resin). It was created. The preparation of the test piece was the same as the manufacturing method already described, and was performed by molding the test piece (CFRP laminate) by the hand lay-up method after the alcohol substitution step and the dispersion step in the epoxy resin. .

  Specifically, first, an ethanol solution having a weight nine times that of MFC was supplied to MFC, and the mixture was stirred for about 10 minutes with a stirring rod. After stirring, water in the stirring liquid was removed by vacuum filtration. Subsequently, an appropriate amount of ethanol is supplied to the MFC that has been made into a sheet by vacuum filtration (a small amount of ethanol remains), and the above-mentioned sheet MFC is loosened with an ultrasonic homogenizer (about 30 minutes). Dispersed. The MFC thus substituted with alcohol was supplied to the main material (epoxy resin), sufficiently stirred with a stirring rod, and then heated to about 90 ° C. in a vacuum furnace to evaporate the alcohol liquid. . Thereby, an epoxy resin (resin composition) in which MFC was uniformly dispersed was obtained. Thus, what made the compounding ratio of MFC with respect to an epoxy resin 0.1 wt% and 0.3 wt% was created. Here, in order to facilitate the dispersion of MFC, a main material (epoxy resin) previously held in an oven at 80 ° C. for about 30 minutes was used.

Using the resin composition and carbon fiber obtained as described above, a CFRP laminate as a test piece was molded by a hand lay-up method. The mixing ratio of the main material and the curing agent was set to 3: 1. Here, when used for a static tensile test, a tensile tensile fatigue test, and a punching impact test, a laminate of the resin composition and the plain weave carbon fiber is placed in a mold having a thickness of 2 mm after molding, The mold was cured at 120 ° C. for 4 hours using a hot press machine capable of pressing at 50 kgf / cm ² (about 490 N / cm ² ). The number of laminated sheet-like carbon fibers was 8 and the fiber volume content after molding was adjusted to 48 ± 2%. On the other hand, when used for an interlaminar fracture toughness test (DCB test, ENF test), while laminating UD (unidirectional) carbon fibers, at the time of lamination, a PTFE film is inserted at the center in the laminating direction for initial crack introduction, A laminate was produced. The number of laminated UD carbon fibers was 12 and the thickness after molding was 3 mm. The other production conditions are the same as those for producing a CFRP plate for a static tensile test, a tensile tensile fatigue test, and a punching impact test. Hereinafter, the details of the test piece for each test will be described.

(1.1) Static tensile test GFRP tabs were attached to both sides and both sides of the CFRP laminate produced in the above process with an epoxy adhesive, and tested into a 2 mm x 25 mm x 200 mm strip shape using a diamond tool. A piece was cut out. The gauge distance was 100 mm. The test piece cut out in this manner was subjected to after cure under the conditions of 60 ° C. × 5 h.

(1.2) Tensile tensile fatigue test A test piece was prepared under the same conditions as the static tensile test.

(1.3) Punching impact test 2 mm x 50 mm x 50 from the CFRP laminate produced in the above process using a table band saw machine
A test piece was cut into a square shape of mm. The test piece cut out in this manner was subjected to after cure under the conditions of 60 ° C. × 5 h.

(1.4) Interlaminar Fracture Toughness Test (1.4.1) Double Cantilever Interlaminar Fracture Toughness (DCB) Test 3 mm × 20 mm × from the CFRP laminate produced by the above process and interposing a PTFE film A test piece was cut out in a strip shape of 150 mm and along the fiber orientation direction (90 ° direction). Under the present circumstances, the width dimension of the PTFE film from a test piece edge part was adjusted to the range of 42-65 mm. And what fixed the block for pin loads to both surfaces of the said film side edge part was used as a test piece.
(1.4.2) End Notch Bending Interlaminar Fracture Toughness (ENF) Test From the CFRP laminate produced by the above process and having a PTFE film interposed, the strip is 3 mm × 20 mm × 100 mm and the orientation direction of the fibers A test piece was cut out along (90 ° direction). Under the present circumstances, the width dimension of the PTFE film from a test piece edge part was adjusted to the range of 42-65 mm.

(2) Experimental conditions (2.1) Static tensile test In accordance with JIS K7073 (Tension test method for carbon fiber reinforced plastic), a static tensile test is performed with displacement control using AUTOGRAPH (manufactured by Shimadzu Corporation). It was. The test speed was 1 mm / min. Further, the load was detected by a load cell, and the displacement was detected by a displacement meter (Axial Extenders 634.11F-21 measurable displacement limit: +5.00 mm / -2.50 mm manufactured by MTS). All tests were performed in a laboratory environment (23 ± 2 ° C., 60 ± 5% RH), and the number of tests under the same conditions was 7.

(2.2) Tensile tensile fatigue test In accordance with JIS K7083 (constant load tension-tensile fatigue test method for carbon fiber reinforced plastic), using an electrohydraulic servo tester (servo pulser rated load: ± 50 ton made by Shimadzu Corporation) A fatigue test was performed under load control. The stress ratio (minimum load stress / maximum load stress) was set to 0.1, and a repeated load was applied as a sine wave waveform with a repetition frequency of 5 Hz. During the test, the laboratory environment (23 ± 2 ° C., 60 ± 5% RH) was always maintained. The test was terminated when the number of repetitions exceeded 10 ⁶ and no fracture occurred, and the fatigue limit was reached.

(2.3) Punching impact test In accordance with JIS K7085 (multi-axial impact testing method for carbon fiber reinforced plastic), a punching test was performed using a high-speed impact testing machine (HYDROSHOT, HTM-10kN manufactured by Shimadzu Corporation). The punching speed was 4.4 m / s. The tip of the striker was hemispherical with a diameter of 12.7 mm, and the test piece was firmly pressure-bonded to the support frame using a dedicated jig. The center position of the 50 mm × 50 mm plane of the test piece was taken as the striker dropping position. In addition, after the maximum load measurement, when the measured load reached 100 N, it was considered that the striker was penetrated and destroyed as a minute force such as a frictional force was acting on the striker. This is because the measured load returns to a positive value again after showing a negative value, or the measured load continues to show a value in the vicinity of 100 N even if the displacement exceeds 5 mm while the specimen thickness is 2 mm. This is due to the presence of the specimen. All tests were performed in a laboratory environment (23 ± 2 ° C., 60 ± 5% RH), and the number of tests under the same conditions was 10.

ここで、
Ｐ_C：初期限界荷重［Ｎ］
Ｐ_R：き裂進展過程の限界荷重［Ｎ］
Ｅ_L：曲げ弾性率［ＧＰａ］
λ ：ＣＯＤ（き裂開口変位）コンプライアンス［ｍｍ／Ｎ］
λ₀：初期弾性部分コンプライアンス［ｍｍ／Ｎ］
Ｄ₁：無次元係数（Ｄ₁≒０．２５）
Ｂ ：試験片幅［ｍｍ］
Ｈ ：試験片厚さ［ｍｍ］
（２．４．２）ＥＮＦ試験
ＪＩＳ Ｋ７０８６（炭素繊維強化プラスチックの層間破壊じん性試験方法）に準拠し、ＡＵＴＯＧＲＡＰＨ（株式会社島津製作所製 定格荷重：１００ｋＮ）を用いて試験速度０．５ｍｍ／ｍｉｎの変位制御で試験を行った。同一条件での試験数を７とした。き裂進展初期におけるモードII層間破壊じん性値Ｇ_IIC［ｋＪ／ｍｍ²］は以下の数式４および数式５に基づき求めた。

ここで、
Ｐ_C：初期限界荷重［Ｎ］
ａ₀：初期き裂長さ［ｍｍ］
ａ₁：初期限界荷重におけるき裂長さ推定値［ｍｍ］
Ｃ₀：初期弾性部分の荷重点コンプライアンス［ｍｍ／Ｎ］
Ｃ₁：初期限界荷重における荷重点コンプライアンス［ｍｍ／Ｎ］
Ｂ ：試験片幅［ｍｍ］
Ｌ ：試験片長手寸法［ｍｍ］ (2.4) Interlaminar Fracture Toughness Test (2.4.1) DCB Test In accordance with JIS K7086 (Interlaminar Fracture Toughness Test Method for Carbon Fiber Reinforced Plastics), AUTOGRAPH (Shimadzu Corporation, rated load: 100 kN) The test was conducted using. In this experiment, crack length, load, and COD (crack opening displacement) were measured every 10 minutes based on the fact that the crack progresses at a stretch. The crosshead speed was 0.5 mm / min before crack growth and 1.0 mm / min after crack growth. The test was terminated when the crack growth length reached 70 mm or when the test piece broke. The number of tests under the same conditions was 5. The mode I interlaminar fracture toughness value G _IC [kJ / mm ² ] in the initial stage of crack growth and the mode I interlaminar fracture toughness value G _IR [kJ / mm ² ] in the crack growth process are respectively It calculated | required based on Numerical formula 3.

here,
P _C : Initial limit load [N]
P _R : Limit load of crack growth process [N]
E _L : Flexural modulus [GPa]
λ: COD (crack opening displacement) compliance [mm / N]
λ ₀ : initial elastic partial compliance [mm / N]
D ₁ : dimensionless coefficient (D ₁ ≈0.25)
B: Specimen width [mm]
H: Test piece thickness [mm]
(2.4.2) ENF test In accordance with JIS K7086 (interlaminar fracture toughness test method for carbon fiber reinforced plastic), the test speed is 0.5 mm / min using AUTOGRAPH (Shimadzu Corporation, rated load: 100 kN). The test was conducted with the displacement control. The number of tests under the same conditions was 7. The mode II interlaminar fracture toughness value G _IIC [kJ / mm ² ] at the initial stage of crack growth was determined based on the following equations 4 and 5.

here,
P _C : Initial limit load [N]
a ₀ : initial crack length [mm]
a ₁ : Estimated crack length at initial limit load [mm]
C ₀ : Load point compliance of the initial elastic part [mm / N]
C ₁ : Load point compliance at the initial limit load [mm / N]
B: Specimen width [mm]
L: Specimen longitudinal dimension [mm]

(3) Experimental results (3.1) Static tensile test The results of the static tensile test are shown in FIG. 1 and FIG. Here, in each figure, the horizontal axis indicates the compounding ratio [wt%] of MFC to the epoxy resin, the vertical axis in FIG. 1 indicates Young's modulus [GPa], and the vertical axis in FIG. 2 indicates tensile strength [MPa]. Each is shown. Moreover, the point shown by the circle mark in FIG. 1 has shown the average value of the Young's modulus for every MFC compounding ratio (same also about FIG. 2). As can be seen from these figures, regarding the static characteristics (Young's modulus and tensile strength), the influence of MFC dispersed in the epoxy resin was not so much. This is considered because the carbon fiber in the longitudinal direction (90 °) bears most of the load.

(3.2) Tensile Tensile Fatigue Test The results of the tensile tensile fatigue test are shown in FIG. In the figure, the horizontal axis indicates the number of repeated fractures [times], and the vertical axis indicates the maximum load stress [MPa]. In the figure, attention is given to the case where the maximum load stress is 500 MPa (76.3%: 0.0 wt%, 72.4%: 0.1 wt%, 76.1%, respectively, with respect to the tensile strength shown in FIG. 2). Then, the fatigue life of CFRP in which 0.1 wt% of MFC was dispersed was extended about three times as compared with that of unmodified (0.0 wt%) CFRP. It was also found that the fatigue life of CFRP in which 0.3 wt% of MFC was dispersed was improved by about 6 times compared with that of unmodified (0.0 wt%) CFRP. From the above, it has been found that the fatigue life of the fatigue characteristics improves as MFC is dispersed in a range of at least 0.3 wt% or less.

Further, when the side surfaces of two types of test pieces (MFC 0.0 wt% dispersed CFRP and MFC 0.1 wt% dispersed CFRP) that reached the fatigue limit when the maximum load stress was 400 MPa were observed with an optical microscope, the following differences were noted: It was observed. That is, a transverse crack can be confirmed on the side surface of the MFC 0.0 wt% test piece, and (i) a crack occurs in the transverse (0 °) direction carbon fiber, which is a fatigue progressing process of the plain weave CFRP. After the crack grew and reached the longitudinal (90 °) carbon fiber, (iii) a process in which the crack progressed along the longitudinal carbon fiber at once was observed. On the other hand, in the side observation of the MFC 0.1 wt% test piece, a crack corresponding to the fatigue growth process could not be confirmed. Although not shown in the figure, when the delamination surfaces of the MFC 0.1 wt% dispersion test piece and the 0.3 wt% dispersion test piece when the maximum load stress is 500 MPa are observed with an SEM (scanning electron microscope), The peeling surface of the MFC 0.3 wt% dispersion test piece showed a complicated peeling surface shape as compared with that of the 0.1 wt% dispersion test piece. In addition, a striation pattern similar to a mirror zone generated on the fracture surface when a crack grew at a relatively low speed was observed on the peeling surface of the MFC 0.3 wt% dispersion test piece. From this, it was found that the crack propagation resistance between the layers was improved by dispersing MFC in the base material (epoxy resin).

ここで、全吸収エネルギＥｔは、最大荷重（計測）時までに吸収されたエネルギＥｉと、最大荷重計測後に吸収されたエネルギＥｐとの和として求めた。また、最大荷重前吸収エネルギＥｉは図４の荷重−変位プロットで囲まれた領域中、最大荷重を境として左側の領域（領域Ａ）の面積に等しく、最大荷重後吸収エネルギＥｐは同右側の領域（領域Ｂ）の面積に等しい。また、延性指標ＤＩは衝撃荷重下における延性評価の指標（ＤＩ＝Ｅｐ／Ｅｉ）であり、エネルギ指数ＥＩは衝撃荷重に対する材料のじん性を表す指標（ＥＩ＝Ｅｔ／Ｅｉ）である。 (3.3) Punching impact test Table 1 below shows the results of the punching impact test. FIG. 4 shows an example of a load-displacement diagram up to penetration failure, and FIGS. 5 to 7 show the degree of dispersion of MFC, absorbed energy before the maximum load, absorbed energy after the maximum load, and The relationship with the total absorbed energy is shown respectively.

Here, the total absorbed energy Et was obtained as the sum of the energy Ei absorbed until the maximum load (measurement) and the energy Ep absorbed after the maximum load measurement. Further, the maximum absorbed energy Ei before the load is equal to the area of the left region (region A) with the maximum load as a boundary in the region surrounded by the load-displacement plot of FIG. It is equal to the area of the region (region B). Further, the ductility index DI is an index of ductility evaluation under impact load (DI = Ep / Ei), and the energy index EI is an index (EI = Et / Ei) representing the toughness of the material with respect to the impact load.

  First, focusing on Ei, it can be seen from the results shown in FIG. 5 that as the amount of MFC dispersion increases, the amount of energy absorbed until reaching the maximum load decreases, and permanent deformation is likely to occur compared to the MFC non-dispersed specimen. On the other hand, focusing on Ep, as shown in FIG. 6, the more MFC is dispersed, the more improved, and Et as well as shown in FIG. 7. It can be seen that the energy that can be absorbed by the time has increased. Further, the ductility index DI is improved as the mixing ratio of MFC is increased (see Table 1). In addition, from the load-displacement curve for each test piece, the more MFC is mixed (dispersed), the more the penetration failure occurs. It was found that the displacement up to (0.0 wt%: 1.961 mm, 0.1 wt%: 2.627 mm, 0.3 wt%: 3.552 mm) increased. From the above results, it was found that by dispersing MFC in the base material, the extensibility to impact load is improved and the toughness is increased.

(3.4) Interlaminar Fracture Toughness Test (3.4.1) DCB Test FIG. 8 shows the relationship between the mode I interlaminar fracture toughness value G _IC and the degree of MFC dispersion at the initial stage of crack growth. FIG. 9 shows the relationship between the mode I interlaminar fracture toughness value G _IR and the degree of MFC dispersion in the crack growth process. As can be seen from these figures, the dispersion of MFC in the base material does not significantly affect the improvement of fracture toughness in the crack growth process, but greatly contributes to the improvement of fracture toughness in the early stage of crack growth. I understood. Specifically, regarding the G _IC of the MFC 0.3 wt% dispersion test piece, an improvement of 61.6% was recognized as compared with that of the MFC 0.0 wt% dispersion test piece.

(3.4.2) ENF Test FIG. 10 shows the relationship between the mode II interlaminar fracture toughness value G _IIC and the degree of MFC dispersion in the early stage of crack growth. From the figure, it was found that crack propagation resistance increased in Mode II due to MFC dispersion. Specifically, regarding G _IIC of MFC 0.3 wt% dispersion test piece,
An improvement of 62.6% was observed compared with that of the FC 0.0 wt% dispersion test piece.

It is a figure which shows the result of a static tensile test, Comprising: It is a figure which shows the influence which the presence or absence of dispersion | distribution of MFC has on Young's modulus. It is a figure which shows the result of a static tensile test, Comprising: It is a figure which shows the influence which the presence or absence of dispersion | distribution of MFC has on tensile strength. It is a figure which shows the result of a tension | pulling tension fatigue test, Comprising: It is a SN diagram which shows the influence which the presence or absence of dispersion | distribution of MFC has on the fatigue life. It is a figure which shows the result of a punch impact test, Comprising: It is an example of the load-displacement diagram until it leads to a penetration failure. It is a figure which shows the result of a punching impact test, Comprising: It is a figure which shows the influence which the presence or absence of dispersion | distribution of MFC has on the absorbed energy before a maximum load. It is a figure which shows the result of a punch impact test, Comprising: It is a figure which shows the influence which the presence or absence of dispersion | distribution of MFC has on the absorbed energy after the maximum load. It is a figure which shows the result of a punch impact test, Comprising: It is a figure which shows the influence which the presence or absence of dispersion | distribution of MFC has on the total absorbed energy. It is a figure which shows the result of an interlaminar fracture toughness test, Comprising: It is a figure which shows the influence which the presence or absence of dispersion | distribution of MFC has on the mode I interlaminar fracture toughness value in the early stage of a crack growth. It is a figure which shows the result of an interlaminar fracture toughness test, Comprising: It is a figure which shows the influence which the presence or absence of dispersion | distribution of MFC has on the mode I interlaminar fracture toughness value in a crack growth process. It is a figure which shows the result of an interlaminar fracture toughness test, Comprising: It is a figure which shows the influence which the presence or absence of dispersion | distribution of MFC has on the mode II interlaminar fracture toughness value in the early stage of a crack growth.

Claims (8)

  A fiber-reinforced composite material obtained by reinforcing a polymer base material with a fibrous reinforcing material, and further comprising microfibril cellulose dispersed in the polymer base material.   The fiber-reinforced composite material according to claim 1, wherein the fibrous reinforcing material is carbon fiber.   The fiber-reinforced composite material according to claim 1 or 2, wherein the polymer base material is an epoxy resin.   The fiber-reinforced composite material according to any one of claims 1 to 3, wherein a weight ratio of the microfibril cellulose to the polymer base material is adjusted to 0.01 wt% or more and 2.0 wt% or less.   The fiber-reinforced composite material according to any one of claims 1 to 4, which is prepreg by semi-curing a polymer base material.   A sports equipment made from the fiber-reinforced composite material according to claim 1.   The sports equipment according to claim 6, which is a ball game tool having a hitting ball part. A method of obtaining a fiber reinforced composite material in which a polymer base material is supplied to a fibrous reinforcing material and solidified thereby to reinforce the polymeric base material with the fibrous reinforcing material,
A method for producing a fiber-reinforced composite material, characterized by supplying a fibrous reinforcing material obtained by dispersing microfibril cellulose in a polymer base material.

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