Stress-relaxation behavior of lignocellulosic high-density polyethylene composites

In this study, stress-relaxation performance of HDPE-based injection-molded composites containing four types of natural fibers (i.e., wood flour, rice hulls, newsprint, and kenaf fiber) at 25 and 50 wt% contents, and the effect of prescribed strain levels were investigated. The results indicated that incorporating more filler causes lower relaxation values and rates, and stress retention and prescribed strain level were reversely correlated. Among the studied filler types, wood flour and kenaf fiber presented more similar behaviors, whereas newsprint resembled rice hulls performance. Strain—time superposition was applied to the experimental data. Due to complex rheological behavior of the studied composites, single horizontal shifting method, with respect to strain levels, was found to be inadequate to satisfactorily superpose data.