Stress relaxation behavior of short pineapple fiber reinforced polyethylene composites

Stress relaxation behavior of short pineapple fiber reinforced polyethylene composites in tension has been studied with special reference to the effect of fiber loading, fiber length, chemical treatment and fiber orientation. Chemical treatments of fiber with reagents such as isocyanate, silane, alkali and peroxide were carried out to improve the interface adhesion between fiber and matrix. The effects of strain level, chemical treatments, pre-straining, and aging on the rate of relaxation have been investigated. It was found that the stress relaxation rate decreases with strain level. It was found that incorporation of fiber results in two relaxation processes. The rate of relaxation is decreased with fiber content. It is observed that chemical treatment has significant influence on the relaxation behavior. Composites containing fibers oriented longitudinally have higher relaxation rate than transversely oriented composites. Aging of samples improved the relaxation modulus due to improved interfacial adhesion at higher temperature. It has been demonstrated that the stress relaxation modulus values measured at different strains can be superimposed by a shift along the logarithmic time axis to yield master curves of modulus over an extended time period.