STUDY OF THE MOLECULAR-STRUCTURE OF PET FILMS OBTAINED BY AN INVERSE STRETCHING PROCESS .1. CONSTANT-SPEED DRAWING OF AMORPHOUS FILMS

The constant rate stretching of amorphous poly(ethylene terephthalate) films is the first step of the industrial ''inverse'' process. To stu dy this process, films deformed under uniaxial planar symmetry conditi ons have been produced on a laboratory stretching machine in order to discuss the influence of macroscopic parameters, such as draw ratio, t emperature and melt viscosity of the amorphous film, on the deformatio n mechanism. The structure of oriented films has been characterized by combining X-ray diffraction and refractive index measurements. Stress strain curves have been simultaneously recorded. The draw temperature and the molecular weight of the polymer are determining factors contr olling the development of molecular orientation and crystalline struct ure in the stretched films. The major influence of relaxation processe s is described and a comparison with constant force drawn films is giv en.