Phase Transition in β-nucleated Isotactic Polypropylene Induced by Combination of Annealing and High Pressure

Abstract

The effects of annealing and high pressure on the microstructure of β-nucleated isotactic polypropylene (iPP) were investigated. Annealing treatment was carried out at different temperatures from 90–170°C under different pressure conditions, that is, atmospheric pressure and high pressures of 150, 250, and 350 MPa, respectively. The microstructure of the specimens was comparatively investigated through using wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Different from the common annealing treatment under atmospheric pressure, which induces the single-phase transition from metastable β-iPP to the more stable α-iPP (β→α) depending on the annealing temperatures, the application of high pressure induces not only the phase transition of β→α but also the phase transition of β→γ. Furthermore, the thermostability of β-iPP was improved greatly under high pressure. The higher the pressure applied, the smaller was the degree of the transition from β-iPP to α-iPP and/or γ-iPP. This work reports, for the first time, a novel crystalline morphology composed of β-iPP and γ-iPP.

Keywords:

• annealing
• β-iPP
• high pressure
• phase transition

Acknowledgments

Thanks for financial support are given to the National Natural Science Foundation of China (51173151, 50973090, 11004163), the Program for New Century Excellent Talents in University (NCET-08-0823), and the Fundamental Research Funds for the Central Universities (SWJTU11CX142, SWJTU11ZT10).