Rheology of short fiber filled thermoplastics

Abstract We examine the applicability of the conformation tensor to describe the fiber orientation and rheology of moderately concentrated fiber‐filled thermoplastics subjected to large deformation flow. To retain computational simplicity, we assume a Newtonian matrix. We present a model that can account for orientation effects, Brownian motion, semiflexibility, and interactions through excluded volume effect, of the fibers. The model predicts a wide variety of rheological effects. We present predictions of steady shear viscosity, primary normal stress and the creep functions, as well as uniaxial elongational viscosity, due to the fibers. We have compared rheological data for 9.54 wt% carbon fibers in polyethylene and 30 wt% glass fibers in polypropylene, with the model predictions. By defining an “effective fiber concentration,” we have been able to correlate the model well with data. With fitting parameters from the steady state viscosity vs. shear rate data, we have been able to predict the steady state primary stress coefficient data as well as the creep data.