Kenichi Takemura

Influence of fiber extraction and surface modification on mechanical properties of green composites with bamboo fiber

Environment-friendly fiber reinforced composites were fabricated using bamboo fibers and vinylester resin by the vacuum assisted resin transfer molding technique. Prior to green composites fabrication, bamboo fiber bundles were extracted by three methods, namely steam explosion, alkali extraction, and chemical extraction. Bamboo fiber bundles were characterized for their interfacial shear strength (IFSS) and tensile properties using the Weibull distribution. The effects of surface modification and water absorption were investigated for green composites with bamboo fibers that were surface-modified by sodium hydroxide (alkali) and silane coupling agent. The tensile properties of bamboo fiber bundle decreased in all conditions compared to raw bamboo fiber, but IFSS increased with chemical treatment due to the effective removal of hemicellulose and lignin from surface of bamboo fiber. The alkali/silane treated fiber composites show higher mechanical and durability properties against water absorption than other surface-modified fiber composites.

Effect of molding condition on tensile properties of hemp fiber reinforced composite

In this study, the effect of molding condition on the tensile properties for plain woven hemp fiber reinforced green composite was examined. The tensile properties of the composite were compared with those of the plain woven jute fiber composite fabricated by the same process. Emulsion type biodegradable resin or polypropylene sheet was used as matrix. The composites were processed by the compression molding where the molding temperature and its heating time were changed from 160 to 190°C and from 15 to 25 min, respectively. The following results were obtained from the experiment. The tensile property of hemp fiber reinforced polypropylene is improved in comparison with polypropylene bulk. The strength of composite is about 2.6 times that of the resin bulk specimen. Hemp fiber is more effective than jute fiber as reinforcement for green composite from the viewpoint of strength. The molding temperature and time are suitable below 180°C and 20 min for hemp fiber reinforced green composite. Hemp fiber green composite has a tendency to decrease its tensile strength when fiber content is over 50 wt%.

Fracture Toughness of Carbon Fiber Reinforced Composites with Rubber Modification

Fracture toughness and the possibility of recycling for Carbon Fiber Reinforced Plastics (CFRP) under mode one and mode two loadings are examined. Epoxy matrix is modified by CNBR rubber particle which diameter is smaller than 100 nano meter. Three kinds of rubber content (5,10,15%) are used. Two types of test methods whose modes are different are conducted. After the specimen fracture, recycled specimens are made by adhesion. Fracture toughness is measured at the tests. Fracture surface is also observed by SEM. As a result, following conclusions are obtained. When the interlaminar fracture test using recycled CFRP specimen is conducted under Mode one loading, fracture toughness is improved using rubber modified matrix. For recycled CFRP specimen under mode two loading, fracture toughness of CFRP using unmodified epoxy is improved. In this case, fracture toughness for modified CFRP is improved but it is not as high as than CFRP with unmodified recycle CFRP. From SEM ovservation on fracture sufface under mode two loading, there is a difference on fracture surfaces. Specimen whose fracture toughness is high has a ductile properties.

Effect of Surface Treatment on Creep Property of Jute Fiber Reinforced Green Composite under Environmental Temperature

In this study, effect of surface treatment on creep property of green composite under environmental temperature was investigated. Jute fiber was used as reinforcement. PLA (polylactic acid) was used as matrix. Surface treatments were conducted using 5 % solution of silane coupling agent and PVA (polyvinyl alcohol). The flexural test was conducted under 25°C environment. The flexural creep test was conducted for 50 hours at 25, 40 and 50°C environment. As a result, the flexural property of composite increased by the surface treatments. And the surface treatments affected the adhesion of fiber/resin interface. Creep strains of surface-treated jute fiber/resin composites were lower than that of virgin composite. The creep strain was decreased by the treatments. The effects are confirmed under various temperature conditions.

Mechanical Properties of Carbon Fiber Reinforced Plastics under Hot-Wet Environment

Water absorption behavior and flexural strength properties of carbon fiber reinforced plastics (CFRP) under hot-wet environment were examined. Those of epoxy resin were also examined for reference. Weight gains of CFRP and epoxy resin were measured after immersion in distilled water at temperatures under 90°C. Quasi-static flexural tests of CFRP and epoxy resin were conducted after immersion for 180 days. Weight gains of CFRP and epoxy resin increased with increasing water temperature. After immersion for 180 days at 90°C, weight gain of CFRP became 3.3times higher and that of epoxy resin was 2.3 times higher than that at RT, respectively. When CFRP and epoxy resin were immersed in distilled water at 90°C, weight gains of CFRP and epoxy resin increased and then decreased. Flexural strengths of CFRP and epoxy resin decreased in distilled water at temperatures less than 90°C. Flexural strengths of dried CFRP and epoxy resin after immersion recovered but were lower than that of virgin CFRP and epoxy resin. Debonding of fiber/resin interface and crack initiation in epoxy resin in distilled water resulted in the strength reduction.

Residual Tensile Property of Plain Woven Jute Fiber/Poly(Lactic Acid) Green Composites during Thermal Cycling

This study investigated the residual tensile properties of plain woven jute fiber reinforced poly(lactic acid) (PLA) during thermal cycling. Temperature ranges of thermal cycling tests were 35–45 °C and 35–55 °C. The maximum number of cycles was 103 cycles. The quasi-static tensile tests of jute fiber, PLA, and composite were conducted after thermal cycling tests. Thermal mechanical analyses of jute fiber and PLA were conducted after thermal cycling tests. Results led to the following conclusions. For temperatures of 35–45 °C, tensile strength of composite at 103 cycles decreased 10% compared to that of composite at 0 cycles. For temperatures of 35–55 °C, tensile strength and Young’s modulus of composite at 103 cycles decreased 15% and 10%, respectively, compared to that of composite at 0 cycles. Tensile properties and the coefficient of linear expansion of PLA and jute fiber remained almost unchanged after thermal cycling tests. From observation of a fracture surface, the length of fiber pull out in the fracture surface of composite at 103 cycles was longer than that of composite at 0 cycles. Therefore, tensile properties of the composite during thermal cycling were decreased, probably because of the decrease of interfacial adhesion between the fiber and resin.

Effect of Water Absorption on Mechanical Properties of Hemp Fiber Reinforced Composite

In this study, the effect of water absorption on mechanical properties of hemp fiber reinforced green composite(HGC) was examined. Plain woven hemp fabric was used as reinforcement. Emulsion type biodegradable resin was used as matrix. The composite was made by compression molding method. Water absorption rate and the effect of the ratio on the mechanical properties were examined. Following results are obtained. The water absorption rate increased with an increase of absorption time. The water absorption rate had an equilibrium state within 30 days. The duration was not dependent on fiber content. In the case of that specimen was kept in water 182 days, the strength decreased 70% of the ultimate one. But in the case that the specimen has dry process after water absorption process, the strength recovered 57%. The recovery ratio is not dependent on water absorption time. The strength reduction rate after dry process is not dependent on fiber content. The strength of resin decreased 62%, and the strength of fiber decreased 13% by water absorption. So the strength reduction of the composite is due to the effect of matrix.

Effect of Resin Particle on Interfacial Shear Strength of CF/MAPP after Immersion

Authors have reported that interfacial shear strength of Carbon Fiber (CF)/Maleic Anhydride grafted PolyPropylene (MAPP) was decreased by immersion for four weeks. As next stage, the purpose of this study is improvement of interfacial shear strength of CF/MAPP after immersion by adding resin particles around fiber. CF and resin particles added CF (RCF) were used as reinforcement. The major axis length of ellipse of resin particles was less than 5μm. In water absorption test, CF/MAPP and RCF/MAPP were immersed in distilled water for four weeks at room temperature. Micro debonding tests of CF/MAPP and RCF/MAPP after immersion were conducted. Fracture morphology of interface between fiber and resin was observed by using scanning electron microscope. As a result, following conclusions are obtained. In case of immersion for four weeks, the interfacial shear strength of RCF/MAPP was greatly increased (70%) compared with that of CF/MAPP. From fracture morphology of RCF/MAPP after immersion, some resin particles on CF surface were found after micro debonding test. Therefore, interfacial shear strength of CF/MAPP after immersion was increased by the effect of resin particles on CF surface.

Effect of Crystallinity on Mechanical Properties of Carbon Fiber Reinforced Polypropylene

In this study, effect of crystallinity on mechanical properties of carbon fiber reinforced thermoplastics (CFRTP) was investigated. Polypropylene (PP) and maleic anhydride modified polypropylene (MAPP) were used as matrix. The crystallinity of PP was controlled by using heat treatment after hot press molding of CFRTP. The range of crystallinity of PP and MAPP were from 26% to 40%. Flexural tests and izod impact tests of CFRTP were conducted based on Japanese Industrial Standard (JIS) K 7074 and JIS K 7110, respectively. As a result, flexural property and izod impact value of CFRTP using PP increased with an increase of crystallinity. However, flexural property and izod impact value of CFRTP using MAPP almost did not change with an increase of crystallinity.

Interfacial Shear Strength of Carbon Fiber Reinforced Polypropylene

In this study, interfacial shear strength of carbon fiber reinforced polypropylene were investigated. Two kinds of reinforcements are used. One is non-treated carbon fiber, another is acetone-treated carbon fiber. And two kinds of matrices are used. One is non-treated polypropylene, another is maleic anhydride-polypropylene. Three point flexural tests and micro debonding tests are conducted. As a result, following conclusions are obtained. Acetone treatment and maleic anhydride are effective to the adhesives on the surface between fiber and matrix. But simultaneous treatments are not effective. The shear strength is not dependent on fiber embedded length. The contact angle and fracture load are dependent on fiber embedded length. The interfacial strength is dependent on the contact angle. As the contact angle increases, the interfacial strength increases.