Effect of the content of β form crystals on biaxially stretched polypropylene microporous membranes and the tuning of pore structures

Abstract

In this article, the content of β crystals in polypropylene (PP) cast films was adjusted by annealing treatment. Subsequently, the effect of the content β crystals on the pore structures and the porosity of PP microporous membranes was investigated. It was found that annealing could improve the long period of lamella stacking and the lamellar thickness, without altering the crystalline morphology and orientation of cast films. The microporous membranes with high porosity and uniform pores and pore-size distribution could be obtained by biaxial stretching. Interestingly, the pore structures of these microporous membranes were quite different. The sample composed of β transcrystals (β-TCs) have only a few or no obvious connecting bridge structures in microporous membranes. However, the sample composed of pure α transcrystals (α-TCs) had a large number of connecting bridge structures, as well as the pores distribution and pore-size distribution were also uniform. These results indicated that the pore structures of microporous membranes could be adjusted by the content of β crystals in PP cast films and homogeneous microporous membranes could also be obtained by biaxial stretching other crystalline forms of PP materials. It afforded a new insight to obtain PP microporous membranes with excellent performance.