Dynamic mechanical behavior of poly[ethylene terephthalate] from 4.2 to 300°K

The dynamic shear behavior of poly (ethylene terephthalate) (PET) has been investigated in the 4.2—300°K temperature region using a freely oscillating torsion pendulum at frequencies of 0.4 to 2 cps. Uniaxial stretching (draw ratio 3:1) of an amorphous specimen resulted in the appearance of a definite maximum in both the damping, δ, and the loss modulus, G', at 30°K (0.7 cps). Filled unstretched PET samples exhibited small loss maxima in the 50—90°K region. For biaxially stretched heat-set specimens the splitting of the β-damping peak (220°K, 1 cps) is found to depend on the orientations of molecular chain axes with respect to the torsion axis.