Linear viscoelastic and transient behavior of polypropylene and ethylene vinyl acetate blends: An evaluation of the linear Palierne and a nonlinear viscoelastic model for dispersive mixtures

Abstract

AbstractBlends of polypropylene/ethylene vinyl acetate (PP/EVA) have been investigated for linear and transient characteristics. The emulsion model developed by Palierne in 1990 is used to characterize the linear viscoelastic properties of the blends. PP/EVA blends with the viscosity ratio of 0.26 and different compositions, such as 90/10, 80/20 and 70/30 wt% PP/EVA have been studied. It was found that the Palierne Model predicts well the linear behavior of all the compositions studied. At low frequencies, some deviation in dynamic moduli was found in case of the 70/30 composition. Structural changes are studied during transient shear flow (step‐up) experiments. A nonlinear rheological model for blends, developed by Peters, Hansen and Meijer (PHM model), is used to describe these transient rheological data. Overshoots and undershoots observed in the experimental data are compared to numerical results obtained with PHM model and explained on the basis of the deformation of the dispersed phase. A modification of the model is proposed in order to get a better description of the behavior of the viscoelastic blend. Predictions of the morphological evolution of the blends under stepwise increase in shear rate experiments were calculated from the modified model and are found to describe the break‐up phenomenon under moderately high shear flow.