MELT RHEOLOGY AND STRAIN-INDUCED CRYSTALLIZATION OF POLYPROPYLENE AND ITS HIGH-DENSITY POLYETHYLENE BLENDS

Melt elasticity and strain-induced crystallization (SIC) conducted under oscillatory shear for two different polypropylene resins: i.e. control-rheology PP and its virgin PP, having similar melt flow rates and polypropylene-high density polyethylene blends were investigated. It was found that the melt elasticity of the virgin PP was only slightly greater than that of the control-rheology PP at the low frequency side, but the induced crystallization rate of the virgin PP was much faster than that of the control-rheology PP. The high molecular weight tails of PP were concluded to play a critical role in determining the SIC rates. The rate was also dependent on the percent of strain imposed within the range of 1 and 10% studied. It increased with increasing strain. The addition of high-density polyethylene increased the melt elasticity of PP, and also slightly increased the quiescent crystallization temperature of PP. However, the SIC rate decreased with increasing HDPE content in the PP/HDPE blends.