Effect of Crystallinity on the Nonlinear Viscoelastic and Optical Properties of Undrawn and Drawn Poly(ethylene terephthalate) Films

Abstract

Simultaneous measurements of dynamic viscoelastic properties with dynamic birefringence in a nonlinear viscoelastic region were carried out for poly(ethylene terephthalate) films having different degrees of crystallinities. Two different types of nonlinear properties were found in undrawn films. One was associated with the slippage of amorphous chains in a low crystallinity region. Another was associated with the slippage of crystallites in the lamellae in a high crystallinity region. In an intermediate crystallinity region, on the other hand, very linear behavior was found. In the case of drawn films, two different nonlinearities were clearly observed. One found in a low crystallinity region was also associated with the slippage of amorphous chains. This nonlinearity might be essentially the same as that in a low crystallinity region of undrawn films. Another was associated with structural changes such as opening of cracks and cavitation in the amorphous region between spherulites or between crystallites, and was found in intermediate and high crystallinity regions. These two nonlinear features were also significantly different in the analysis with the ERSISC and non-linear Voigt element.