STRESS-RELAXATION BEHAVIOR OF SHORT PINEAPPLE FIBER-REINFORCED POLYETHYLENE COMPOSITES

Stress relaxation behavior of short pineapple fiber reinforced polyeth ylene composites in tension has been studied with special reference to the effect of fiber loading, fiber length, chemical treatment and fib er orientation. Chemical treatments of fiber with reagents such as iso cyanate, silane, alkali and peroxide were carried out to improve the i nterface adhesion between fiber and matrix. The effects of strain leve l, chemical treatments, pre-straining, and aging on the rate of relaxa tion have been investigated. It was found that the stress relaxation r ate decreases with strain level. It was found that incorporation of fi ber results in two relaxation processes. The rate of relaxation is dec reased with fiber content. It is observed that chemical treatment has significant influence on the relaxation behavior. Composites containin g fibers oriented longitudinally have higher relaxation rate than tran sversely oriented composites. Aging of samples improved the relaxation modulus due to improved interfacial adhesion at higher temperature. I t has been demonstrated that the stress relaxation modulus values meas ured at different strains can be superimposed by a shift along the log arithmic time axis to yield master curves of modulus over an extended time period.