CHANGE OF DYNAMIC VISCOELASTIC PROPERTIES OF THE BIAXIALLY STRETCHED POLY (ETHYLENE TEREPHTHALATE) FILMS

Abstract

In the series of investigation (Parts 10-12), the effect of molecular (crystalline and amorphous) orientation on the mechanical properties of biaxially stretched poly(ethylene terephthalate) (PET) films prepared by a dryprocess are further studies made on the effects of crystallinity and molecular orientation on dynamic properties of biaxially stretched polypropylene and poly (vinyl chloride) films are reposted (Parts 7 and 13). In this paper, studies have been made on the effects of crystallinity and molecular orientation on dynamic viscoelastic properties of biaxially stretched PET films.The following results were obtained.(1) Profiles characteristic to the dynamic viscoelastic properties, given as a function of temperature change depending on the orientation mode, degree of orientation and crystallinity.(2) The anisotropy of dynamic modulus of PET films stretched under various conditions are related to the anisotropy of Young's modulus.(3) E''max value and the temperature at which the E''max appears depend on the crystallinity and the over-all degree of molecular orientation. The deformation mechanism of PET films during stretching were, therefore, analyzed in detail in terms of E''max and the temperature.(4) The temperature at which tan δmax was observed, corresponding to the glass transition temperature, was independent of the stretching direction of the film but it increased with increasing stretch ratio. The molecular chains seem to be more extended and restricted in the uniaxially stretched films than in the biaxially stretched films.