Micropore formation and crystalline evolution during biaxial stretching process of iPP film constructed of ordered and continuous β-transcrystallinity

Since biaxial stretched polypropylene (PP) microporous membrane was increasingly popular and crucial in scientific research and industrial production, the problems of less porosity and uneven micropore distribution urgently awaited solution. To further explore these issues, two kinds of iPP films, one constructed of continuous and ordered β transcrystallinity and the other constructed of β spherulite, were introduced into synchronous biaxial stretching process in this work. The experiments demonstrated that the direction of β lamellae arrangement along the force field played a key role in the micropore formation and crystalline evolution. As a result, the lamellae in β transcrystallinity were easier to be separated to form micropores and the crystalline transformation process was steadier, hence contributing to the higher porosity, less stems and much more uniform distribution. In practice, the microporous membrane stretched from the β transcrystallinity film achieved considerable enhancement in separation performance as well as the permeation property. Furthermore, an interpretation model concerning the relevance between the initial lamellae arrangement and microporous membrane property was proposed, providing fresh insights on how to produce microporous membrane with better performance.