Rheological Investigation on a Polypropylene/Low Density Polyethylene Blending Melt

Polymer blending with co-continuous morphology has garnered the interest of many researchers, but corresponding rheological models are rarely presented. In this study, the dynamic rheological behavior of a blend of polypropylene (PP) and low-density polyethylene (LDPE) in the ratio of 50/50 wt% is investigated, and a rheological model suggested by Yu et al. is used to fit the dynamic modulus. The rheological measurement shows that at low frequency, pure PP has higher complex viscosity and dynamic modulus than LDPE. SEM images reveal that the morphology among the 40/60 and 60/40 blends is non-dispersive. The fitting results indicate that the data at low frequency are underestimated by Yu model with lower coefficient KC, while the data are well-fit by the model with enough KC. Furthermore, the coefficient KB has no obvious influence on the fitting since B type structure in the original Yu model has a very weak contribution to dynamic modulus when orientation and distortion of the cylinders standing for the co-continuous structure cannot be neglected. The key coefficients in Yu model are KC and the characteristic length lc, while the co-efficient KB can be neglected. Thus, a simplified form of the model is suggested to predict the rheological dynamic modulus data for the PP/LDPE blending melt.