Anomalous Melt Rheological Properties of Unimodal-MWD HDPE Blends

The melt rheological behaviors in both linear and nonlinear regions were studied for binary blends of high-density polyethylenes (HDPEs) with unimodal molecular weight distribution (MWD). The surface distortion of the component resin with high-molecular-weight (HMW) and wide MWD through the capillary die could be alleviated with the addition of the component resin with low-molecular-weight (LMW) and narrow MWD. At the concentration of LMW component resin above 50 wt%, the negative deviation behavior (NDB) was observed in both the plots of dynamic storage modulus and complex viscosity versus the composition of the blends, furthermore, the Cole-Cole plot of the blend was below that of the pure LMW component, indicating the characteristics of immiscibility. However, the characteristic of homogeneity was revealed in the logG′～logG″ curves that possessed almost identical slopes for all the blends. The anomalous phenomena were attributed to the slow diffusion of HMW ingredients in the blends, which was aggravated by the inefficient stress transfer during melt blending at high concentration of LMW component.