Anomalous Optical Anisotropy of Oriented Cellulose Triacetate Film

Abstract

Effect of uniaxial strain on optical anisotropy for a cellulose triacetate (CTA) film was investigated by simultaneous measurements of stress and birefringence. Strain rates at hot-stretching process hardly affected orientation birefringence of CTA, although stress level increased with increasing the strain rate. Furthermore, birefringence was found to decrease only slightly after the cessation of the hot-stretching, i.e., stress relaxation process, beyond its glass transition temperature. Wide-angle X-ray diffraction patterns revealed that the orientation of crystals in the stretched film was not relaxed during the stress relaxation process. These results indicate that the orientation birefringence of CTA is mainly determined by the orientation of crystals.