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

Abstract

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

Comparison of the Structural Evolution of β Polypropylene During the Sequential and Simultaneous Biaxial Stretching Process

“…Compared with other polymers used to manufacture membranes, polypropylene (PP) has a unique advantage in terms of solvent resistance property, mechanical and processability properties as well as price. Currently, the most commonly used manufacturing process for PP microporous membrane is the "dry process", which mainly includes the uniaxial stretching method and sequential biaxial stretching method [6][7][8][9][10][11][12][13]. While the uniaxial stretching method is difficult to achieve continuous production due to the treatment of precursor film and the microporous membrane prepared by this process has very low lateral mechanical properties.…”