VISCOELASTIC RELAXATION IN ORIENTED SEMICRYSTALLINE POLYMERS

This paper presents a theoretical and experimental investigation of the basic mechanism controlling viscoelastic relaxation in oriented semicrystalline poly(ethylene terephthalate) (PET). We have analysed the anisotropic elastic moduli, creep behaviour and structural relaxation. The master creep curves and shift factors are constructed. The study helps us to separate the crystalline and amorphous contributions to the micro-deformation in oriented films. We find that (1) the crystal orientation and shape define the unrelaxed anisotropic moduli, and (2) the relaxation timescale is mainly determined by the amorphous region within PET. The calculation also reveals that the relaxation-time spectrum is very broad due to the presence of crystallites. A comparison between the theory and experiment is made.