Measurements and Comparison to Predictions of Viscosity of Heavily Filled HDPE with Natural Fibers

Abstract Composites of rice hulls at various levels of loadings in recycled HDPE were characterized rheologically using a conical extrusion die and small amplitude oscillatory shear (SAOS) measurements. Although the results do not match, due to the invalidity of the Cox–Merz rule for such composites, both types of measurements indicate that increasing the filler concentration results in significantly higher viscosities and increased shear thinning. The errors associated with the use of a conical die due to viscous dissipation are assessed through computer simulations. They are small for relatively small throughputs (small pressure drops). The experimental results for viscosity are compared to predictions of the Einstein–Batchelor equation for suspensions of spherical particles, the Guth–Simha equation, and the empirical Krieger–Dougherty correlation, for filler loadings of up to 70% by weight. The comparison indicates that reasonable approximations of the consistency index of the power law viscosity model are possible through using the above expressions for loadings up to perhaps 40–50% by weight.