Studying the Peculiar Shape Memory Effect of Isothermally Cold Crystallized Poly(ethylene terephthalate) Films

Poly(ethylene terephthalate) is one of the most applicable hompolymers worldwide. In 1952, PET was introduced as an anti-crease fabric that didn’t need ironing [1]. Being anticreaseis associated with capability of recovering original shape as result of internal stresses. Although such stresses arehardly sensible but could affect skin and muscles. Besides, there might remain some residual creases after removing external force. In order to solve such problems a new propertycould be incorporated in the structure of fabrics that make the original shape back in response of an external heat stimuli.Such property is called shape memory effect and originates from a two-phase structure with two different transition temperatures. Most of the shape memory polymers found inliterature are consisted of at least two polymer components such as block copolymers specially polyurethanes [2,3].Consequently a homopolymer like PET is not mentioned as a shape memory substance at first discretion; but taking a closerlook to the coexistence of crystallites and amorphous phase in its semi-crystalline structure leads to the theoretical two phasemodel. The aim of this study is to predict shape memory property of PET. Glassy PET films were isothermally crystallized at different temperatures and time durations.Structural analyses such as DSC, WAXD and stress relaxation tests were employed to determine the structure. Finally shape memory properties were investigated through performing some bending tests. The results show that higher recovery belongs to the sample treated at low temperatures and short time durations of crystallization.