Self‐Toughening and Self‐Reinforcing Injection‐Molded Isotactic Polypropylene via Midfrequency Vibration Field

The effect of vibration frequency on the mechanical properties of general grade polypropylene (PP) prepared by two types of vibration injection molding (VIM) was investigated. With the application of vibration injection molding, the mechanical properties of isotactic PP are improved. The yield strength was upgraded with the increment of vibration frequency and a peak occurs at a particular frequency for each VIM. The elongation at break was also raised by increased vibration frequency, and the vibration frequency also improves impact strength. Self‐reinforcing and self‐toughening polypropylene molded parts were found at high vibration frequency. The wide angle X‐ray diffraction (WAXD) curves and scanning electronic micrograph (SEM) micrographs have shown that, in the vibration field, the enhancement of mechanical properties can be attributed to the occurrence of a γ‐phase crystalline structure and a more pronounced elongation in shape than obtained by conventional injection moldings. In addition, smaller crystals of the β‐phase crystal form improve toughness.

Keywords:

• vibration
• injection molding
• isotactic polypropylene
• reinforcement
• toughness

Acknowledgments

Contract grant sponsors: National Natural Science Funds of China (50473053, 10590352); Key Project of Chongqing Science and Technology Commission (CSTC, 2005AA3012‐5); Science Funds of Chongqing Institute of Technology (2005ZD21).