ANISOTROPY OF DYNAMIC VISCOELASTICITY FOR UNIAXIALLY DRAWN POLY(ETHYLENE-TEREPHTHALATE) FILMS AND ITS TEMPERATURE-DEPENDENCE

The dynamic moduli (E(theta)') in various directions making angles-theta with the drawing direction were measured for the zone-drawn and zone-annealed PET films. In the case of the zone-drawn film, the E0' was 7.7 GPa and the E90' was 2.1 GPa at 25-degrees-C. All E' values decreased monotonically with increasing temperature up to ca. 100-degrees-C. However, those E(theta)' values above 160-degrees-C became almost the same and were independent of theta. The E0' and E90' of the film zone-annealed at 200-degrees-C were 15.6 GPa and 2.3 GPa at 25-degrees-C, respectively. The E0' value is double, but the E90' value was the same as those of the zone-drawn films. In order to evaluate the temperature dependence of the E' anisotropy, the degree of E' anisotropy at various temperatures, psi(T), was defined as follows: psi(T) = {E0'(T) - E90'(T)}/E0'(T). The psi(T) values for the zone-drawn film were constant up to 100-degrees-C, but decreased with increasing temperature above 100-degrees-C. On the other hand, the psi(T) values for the zone-annealed film were constant over the temperature range from 25 to 220-degrees-C. Above 200-degrees-C, the zone-drawn film was almost isotropic, whereas the zone-annelaed film showed a high anisotropy.