DEVELOPMENT OF MOLECULAR-ORIENTATION IN SEQUENTIALLY DRAWN PET FILMS

A study has been made of the transverse stretching of poly(ethylene te rephthalate) film previously drawn longitudinally at constant force an d width. The crystalline phase has been characterized using wide-angle X-ray diffraction: the orientation of the chain axis and the normal t o the phenylene ring have been determined, as well as the crystallite size. Infra-red spectroscopy and refractive index measurements have be en used to characterize the orientation of the material averaged over the crystalline and amorphous phases. The results showed that the crys tals, which were preferentially aligned with their chain axes along th e first stretching (longitudinal) direction, break down during the sec ond drawing and that recrystallization takes place to produce crystall ites with their c-axes aligned along the transverse stretching directi on. The observed increase in the tendency for the normal to the phenyl ene ring to be normal to the film plane correlates with the increase i n crystallite size along the chain axis for crystallites oriented with their chain axes in the transverse direction.