Recovery Behavior of Amorphous Poly(Ethylene Terephthalate) Film Uniaxially Drawn at Different Temperatures

Abstract

Homogeneously deformed amorphous poly(ethylene terephthalate) (PET) film samples were obtained by uniaxial drawing at temperatures from near the glass transition temperature T g to far above T g. Isothermal dimensional recovery behavior was studied for the free stress state of the deformed sample. It was shown that the dimensional recovery behavior of samples drawn near T g was different from that of a sample drawn about 20°C above T g, indicating that the deformation mechanisms changed when the drawing temperature rose from near T g to far above T g. Recovery curves of samples drawn near T g show two distinct steps in log time scale; the second step follows a single exponential function. The infrared measurement of a drawn sample showed that the dichroic function decreased during recovery in the first step and was almost invariant at a very low value (<0.03) in the second step. However, the recovery curve of samples drawn about 20°C above T g demonstrated nearly a straight line in log time scale.