The effect of orientation on the morphology and viscoelastic response of vinyl alcohol-ethylene copolymers

Full Paper: The influence of the main variables (temperature and strain rat e) of the drawing process on the structure and dynamic mechanical relaxatio ns of vinyl alcohol-ethylene (VAE) copolymers with higher content in the fo rmer counit is studied. The structure of VAE copolymers is considerably mod ified by drawing, which produces a disordered crystalline farm. as revealed by WAXD and DSC measurements. The structural changes have significant effe cts on the viscoelastic relaxations of stretched VAE copolymers. A remarkab le increase in the storage moduli is observed in the direction parallel to the uniaxial orientation, depending on composition and drawing parameters, The drawn copolymers show an additional a relaxation taking place at temper atures higher than that of the a relaxation (glass transitions), attributed to motions within the crystalline regions. The beta mechanism is moved to higher temperatures for the stretched specimens slid its intensity is consi derably increased. Finally, the gamma relaxation is very weak and only disp layed in the sample with the higher ethylene content.