Vibration-dependent morphology and crystal structure of isotactic polypropylene

Abstract

A small homemade device was used to study the influence of mechanical vibration on the crystal structure and morphology of isotactic polypropylene (iPP) under different melting temperatures, vibration times, vibration frequencies, and cooling rates. The crystallite size, crystal structure, and crystallinity of iPP under or without vibration treatment were investigated by means of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and polarized microscopy observation (PLM). The crystallization of iPP varied with the length of vibration time, vibration frequency, cooling rate, and melt temperature. Compared with the data of conventional samples measured by DSC, vibration could increase the crystallinity of iPP, make melting peak of α-crystal move toward higher temperature and make that of β-crystal shift to lower temperature. Meanwhile, WAXD measurements showed that the vibration could reduce the content of β-crystal evidently, particularly at the lower vibration frequency, lower cooling rate, and higher melting temperature. Furthermore, PLM measurements showed that the vibration made the spherulite size smaller.