The use of large transient deformations to evaluate rheological models for molten polymers

Abstract

The prediction of models proposed by Acierno et al. (ALMRT) and by Phan-Thien and Tanner (PTT) are compared with data for a low density polyethylene film resin and a high density blow molding resin. The deformations involved are interrupted shear, reduction in shear rate, large amplitude oscillatory shear and uniaxial extension. Both models predict characteristic times for ”reentanglement“ that are significantly larger than stress relaxation times, but that are still much smaller than observed values. The origin of this effect is shown to be quite different in the two models. The ALMRT model fails to predict the observed nonlinearity in the response to large amplitude oscillatory shear. The PTT model predicts nonlinearity and gives the correct value of the maximum stress, but the predicted shape of the stress curve is incorrect. Extensional stress growth data were not in agreement with the predictions of the ALMRT model except in the linear region. It was not possible to fit the PTT model to these data.