POLYMER ENGINEERING AND SCIENCE, NOVEMBER 2002, Vol. 42, No. 11 2107 INTRODUCTION T he relationship between rheology and morphology of emulsions and polymer blends is of impor- tance, theoretically and experimentally, in order to understand the evolution of the two-phase morphol- ogy during mixing, since this morphology governs the final properties of the end product. By choosing the ad- equate composing polymers for the blend, it is possible to obtain a large range of properties. Blend properties in the liquid/liquid phase are generally influenced by various factors such as the rheological characteristics of the components, composition, interfacial tension, do- main structure etc. (1–3). For the linear regime of the viscoelastic behavior, the Palierne model (4) is known to give rather good results in predicting the blend properties from the component properties and the 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 SANDEEP TYAGI and ANUP K. GHOSH* Centre for Polymer Science and Engineering Indian Institute of Technology, Delhi Hauz Khas, New Delhi-110016, India and P. MONTANARI, G. W. M. PETERS, and H. E. H. MEIJER Materials Technology Dutch Polymer Institute Eindhoven University of Technology P.O. Box 513, 5600 MB Eindhoven, The Netherlands Blends 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. Over- shoots and undershoots observed in the experimental data are compared to numer- ical results obtained with PHM model and explained on the basis of the deforma- tion 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 mor- phological evolution of the blends under stepwise increase in shear rate experi- ments were calculated from the modified model and are found to describe the break-up phenomenon under moderately high shear flow. *Corresponding author: Email: akghosh@polymers.iitd.ernet.in