Influence of annealing on stress-strain behaviors and performances of beta nucleated polypropylene stretched membranes

摘要

In this article, two beta nucleated polypropylene (beta-iPP) precursor films were prepared through crystallizing at 110 and 135 degrees C. The differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM) and tensile testing were employed to investigate the influence of annealing on stress strain behaviors and performances of biaxial stretched membranes. The traditional time consuming annealing treatment demonstrates that within the most favorable annealing temperature window of 130-140 degrees C, only a small fraction of thin beta lamellae melted and recrystallized to form more stable beta phase, resulting in the slight improvement of the stress strain behaviors and performances of beta-iPP membranes. Furthermore, a rapid annealing method was designed, involving a short time thermal stimulus at high temperature and then cooling in the air. During this process, substantial melting and epitaxial crystallization of less stable beta crystal occurred, leading to the apparent thickening of beta lamellae and the narrowing of beta lamellar thickness distribution. Consequently, the stress-strain behaviors of beta-iPP films and performances of biaxial stretched membranes were improved significantly.