The influence of molecular weight distribution of industrial polystyrene on its melt extensional and ultimate properties

Abstract

We analyze the linear viscoelastic behavior and the strain‐rate dependence of nonlinear viscoelastic as well as the ultimate extensional properties of industrially relevant linear polystyrene mixtures (PS). The studied materials comprise different miscible binary mixtures of a well entangled matrix and unentangled diluent resulting in bimodal molar mass distribution (MWD). We also analyze the effect of the diluent weight average molar mass (Mw) by comparison with a mixture having broad but monomodal MWD. We show that the dilution effect on linear rheological properties is in agreement with the theoretical value of unity for the dilution exponent. We further show that the processing window, expressed as the ability of the material to withstand a given load without loss of homogeneity during elongation or ultimate loss of cohesion, is affected differently depending on the diluent Mw and concentration. Finally, we conclude that the existence of strain hardening is not sufficient for complete characterization of extension dominated operations. Our results demonstrate that significant enhancement of strain hardening achieved by adding small‐Mw diluents is often accompanied by trade‐off with respect to failure behavior of these mixtures. POLYM. ENG. SCI. 56:1012–1020, 2016. © 2016 Society of Plastics Engineers