Pore growth and stabilization in uniaxial stretching polypropylene microporous membrane processed by heat-setting

To clarify the pore growth and stabilization process, the heat-setting process during the preparation of polypropylene microporous membranes was followed. It was found that pore size increasing during heat-setting was attributed to the stabilization of stretching-induced connecting bridges through crystallization and lateral shrinkage within amorphous region. The stretching-induced stable connecting bridges came from the secondary crystallization of stretched tie chains and the conversion of some unstable lamellae to fiber crystals through melting and recrystallization behavior. After stretching, during the heating process to heat-setting temperature, it was mainly the melting and recrystallization behavior that decreased the retraction of bridges. During the following heat-setting, the secondary crystallization of stretched tie chains further stabilized the connecting bridges. At the same time, the lateral shrinkage within amorphous region during heating and heat-setting further lead to the pore size increasing. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1604–1614