Understanding in the morphology and tensile behavior of isotactic polypropylene cast films with different stereo-defect distribution

Abstract

In this study, two iPP resins with similar molecular weight and average isotacticity but different uniformities of stereo-defect distribution were used in the production of cast films. The crystalline morphology and orientation, and tensile behavior during room temperature stretching of the cast films were investigated by scanning electronic microscopy (SEM), 2D-wide angle X-ray diffraction (2D-WAXD) and 2D-small-angle X-ray scattering (2D-SAXS). It was found that under fixed processing condition, iPP with more uniform stereo-defect distribution (PP2) favors the formation of row nucleated lamellar structure during cast film production, and therefore exhibiting hard-elastic deformation behavior during stretching; meanwhile, the sample with less uniform stereo-defect distribution (PP1) shows un-oriented spherulitical morphology in the cast film, and typical plastic deformation behavior during stretching. The crystallization and rheological analysis on the iPP raw materials revealed that, the uniformity of stereo-defect distribution determines the ability of nucleation and crystallization, and further influences the response of the crystalline morphology to the elongation effect of cast film production process, which is of great importance in the structure–property design in the production of iPP membranes.