On the Strain‐Induced Crystalline Phase Changes in Semi‐Crystalline Polymers: Mechanisms and Incidence on the Mechanical Properties

Abstract

This is a critical survey of the phenomenon of strain‐induced crystalline phase changes in semi‐crystalline polymers. This paper is not concerned with the strain‐induced crystallization of glassy polymers. An examination is made of the experimental data reported in literature, together with a discussion about the mechanism of crystalline phase transitions and about the benefits or prejudices which result on the materials properties. Special attention has been paid to the most largely documented polymers which include materials having either van der Waals, or hydrogen or polar inter‐chain bonding. This concerns polypropylene, polyamide 6, ethylene/vinyl‐alcohol copolymers, poly(vinylidene fluoride) polyesters, and polyethylene. An additional section is devoted to several series of much less documented polymers, from the standpoint of crystal phase changes. Although most of the cases are dealing with films and fibers submitted to tensile drawing, some of the reported studies are concerned with bulk materials. An attempt is made to establish guidelines for the mechanisms of crystalline phase changes based on chain conformation, thermodynamic stability, and plasticity defects.