Uniaxial stretching induced pore nucleation and growth in row-nucleated crystalline hard-elastic polypropylene film: The effect of activation volume and stretching work

Abstract

In this paper, the pore nucleation and growth during uniaxial stretching of polypropylene hard-elastic film at different temperatures were followed. The stretching-induced microstructure including lamellar clusters, fibrillar crystals and pores were tracked by in-situ x-ray scattering. The correlation between activation volume and lamellar clusters thickness and the relationship between stretching work and the new formed fibrillar crystals/pore surface area were built. It was found that compared with that obtained at 105 °C, the hard-elastic film stretched at 145 °C induced larger lamellar cluster thickness, longer fibrillar crystals and fewer pores with larger size. With the stretching temperature increasing, the chain segment activation volume increases, whereas the activation energy and stretching work decreases. During uniaxial stretching, the stretching work was mainly dissipated by forming new surfaces. Higher activation volume lead to larger lamellar cluster thickness and less pore number in unit area, whereas lower activation energy induced longer fibrillar crystals and lower stretching work resulted in less new surface. This paper clarifies how the stretching temperature affect pore formation and growth during the uniaxial tensile deformation of hard elastic film and the obtained results are beneficial for the pore control during the industrial fabrication of polypropylene microporous membrane.