Influence of annealing on stress–strain behaviors and performances of β nucleated polypropylene stretched membranes

Abstract

In this article, two β nucleated polypropylene (β-iPP) precursor films were prepared through crystallizing at 110 and 135 °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 °C, only a small fraction of thin β lamellae melted and recrystallized to form more stable β phase, resulting in the slight improvement of the stress–strain behaviors and performances of β-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 β crystal occurred, leading to the apparent thickening of β lamellae and the narrowing of β lamellar thickness distribution. Consequently, the stress–strain behaviors of β-iPP films and performances of biaxial stretched membranes were improved significantly.