EFFECTS OF MORPHOLOGY OF POLY(BUTYLENE TEREPHTHALATE) ON THERMAL PROPERTIES AND STRUCTURE OF POLY(LACTIC ACID) MICROPOROUS FILMS FABRICATED BY BIAXIAL STRETCHING TECHNIQUE

Abstract

The aim of this research is to investigate the effects of morphology including shape and size of dispersed phase on the properties of microporous films fabricated by biaxial stretching technique. The microporous films were prepared from the composites containing poly(lactic acid) (PLA) as a polymer matrix and poly(butylene terephthalate) (PBT) as a dispersed phase. The composites containing spherical and fibrous PBT with different particle and fiber sizes were prepared by adjusting initial composition, mixing temperature and mixing protocol of internal batch mixer and capillary rheometer. Scanning electron microscopic results show that PBT fibers can be produced by melt-stretching and subsequently fast quenching. Rheological characterization confirms the random network structure of PBT fibers. Moreover, it is found that PBT is a nucleating agent accelerating the crystallization rate of PLA, particularly PBT fibers having large specific surface area. The stretched films composed of spherical particles exhibit the ellipsoidal microvoids owing to interfacial debonding of polymer chains. The size of spherical PBT particles affects the void size but not influences the void content of the stretched films. The void content considerably increases to about 8% for the stretched films containing dispersed fiber because of the localized deformation between interdigitated fibers. In addition, the stretched films have increased crystallinity and reduced heat of cold crystallization as a result of strain-induced crystallization, especially at high stretching ratio.