High Performance Kenaf Fiber Reinforced Plastics by Surface Modification and Recycling Method

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Kenaf fiber was collected from the kenaf, Hibiscus cannabinus L. in order to use the reinforcing fiber of FRP. Mechanical properties of kenaf FRP and recycling methods were investigated.The bast (skin) of kenaf stem was treated in 5wt% sodium hydroxide solution at 80℃. Kenaf fiber was obtained after neutralization, washing, and drying. Two types of kenaf fiber were prepared ; 5 mm length short fiber for random orientation FRP and continuous fiber for unidirectional FRP. In the case of long fiber, preforms were fabricated by arranging bundles of long fiber in one direction and pressing. The preforms were impregnated by unsaturated polyester resin and then cured. Three point bending tests of kenaf FRP were carried out to evaluate flexural strength and modulus.The fiber content limit was 30wt% for random orientation FRP. The strength and modulus of FRP decreased in the low fiber content region and they recovered by filling more fibers. In the case of unidirectional long fiber FRP, the fiber content could be 50wt%. The flexural strength of unidirectional FRP was 3 times as large as that of neat resin. The flexural modulus was 5 times.The silane treated kenaf was used in order to improve the interfacial bonding. In the low content region, the treatment was effective. On the other hand, the properties of treated kenaf FRP were not improved remarkably in the high content region.Chemical decomposition of kenaf FRP was tried by using alkaline solution for the purpose of recycling. It was difficult to decompose sufficiently to low molecular weight. Then, crushed particles of kenaf FRP was used as filler of kenaf FRP as material recycling. The mechanical properties of recycled kenaf FRP could be stated good in general by optimizing the constitution of laminates.