Melt rheological behavior of intimately mixed short sisal-glass hybrid fiber-reinforced low-density polyethylene composites. I. Untreated fibers

The melt rheological behavior of intimately mixed short sisal-glass hybrid fiber-reinforced low-density polyethylene composites was studied with an Instron capillary rheometer. The variation of melt viscosity with shear rate and shear stress at different temperatures was studied. The effect of relative composition of component fibers on the overall rheological behavior also was examined. A temperature range of 130 to 150degreesC and shear rate of 16.4 to 5470 s(-1) were chosen for the analysis. The melt viscosity of the hybrid composite increased with increase in the volume fraction of glass fibers and reached a maximum for the composite containing glass fiber alone. Also, experimental viscosity values of hybrid composites were in good agreement with the theoretical values calculated using the additive rule of hybrid mixtures, except at low volume fractions of glass fibers. Master curves were plotted by superpositioning shear stress and temperature results. The breakage of fibers during the extrusion process, estimated by optical microscopy, was higher for glass fiber than sisal fiber. The surface morphology of the extrudates was analyzed by optical and scanning electron microscopy. (C) 2003 Wiley Periodicals, Inc.