Influence of High-Density Polyethylene and Nano-Calcium Carbonate of Various Content Ratios on the Crystallization of Polypropylene

Abstract

The influence of high-density polyethylene (HDPE) and nano-CaCO₃ of various content ratios on the crystallization of polypropylene (PP) was investigated by differential scanning calorimetry, dynamic rheology, wide angle X-ray diffraction (WAXD), and Izod impact strength measurements. The results showed that HDPE and PP were phase separated in their blends and the additive CaCO₃ filler mainly dispersed in the PP phase, acting as a nucleation agent to promote the crystallization of PP. For the samples HDPE/ nano-CaCO₃ 30/0 and 25/5, the β crystals content was much higher than the other samples. The reason is that the viscosity difference between HDPE and PP led to a velocity difference, which could induce shear stress at the interfaces of HDPE and PP during injection molding. The intensive shear stress at their phase interfaces is advantageous for orientation of the chains, inducing the formation of β crystals. However, with the increment of CaCO₃ content, there were dual effects of CaCO₃ on the crystallization of PP: at low CaCO₃ content, it would hamper the orientation of PP chains, thus leading to a decrease of β crystals; at high CaCO₃ content, it would induce β crystals by itself.

Keywords:

• β crystals
• CaCO₃
• high-density polyethylene
• phase interface
• polypropylene

Acknowledgments

We express our great thanks to the special fund for the State Key Laboratory for financial support. We are indebted to the National Synchrotron Radiation Laboratory (NSRL) at the University of Science and Technology of China and Prof. Guoqiang Pan (NSRL) for his help in the WAXD.