Sequential biaxial drawing of polypropylene films

Polypropylene cast films were drawn successively in two perpendicular directions at temperatures near the melting point. In order to investigate the structure formation along the deformation path the transverse draw ratio lambda(TD) was varied between 1 and 9. Quantitative X-ray texture analysis, small angle X-ray scattering and atomic force microscopy were used to characterize the structure of the films on a molecular and supermolecular level. Additionally, the melting behavior and the mechanical properties were investigated. The results of the experimental investigations show, that the first deformation step (MDO Process) transforms the initially spherulitic morphology of the cast film into a stacked lamellae morphology (shish kebab) by partial melting. This stacked lamellae morphology is deformed during the transverse drawing (TDO process) into a fibrillar network under the action of crystallographic slip processes ((010)[001] and (110) [001] slip). Further deformation orients the fibrils towards the actual draw direction. The observed structural changes correlate with the melting behavior and the mechanical and thermomechanical properties of the films. (C) 2004 Elsevier Ltd. All rights reserved.