A deformation induced order‐disorder transition in isotactic polypropylene

In this study, isotactic polypropylene (i‐PP) has been deformed by uniaxial compression to draw ratios up to 16×, and at draw temperatures from 30°C to 140°C. An order‐disorder transition in the crystals is observed at draw temperatures well above the stability limit, 70°C, reported for the disordered phase; Furthermore, this disordered phase (called smectic) is found to induce ductility and improve the efficiency of draw. The deformation induced smectic phase has been characterized using WAXS, DSC, and on‐line compression load versus draw ratio measurements. In consequence, a set of process conditions are offered to optimize draw. A mechanism for plastic deformation of i‐PP is also suggested, using the smectic phase as a probe. Copyright © 1988 Society of Plastics Engineers