EFFECTS OF CRYSTALLIZATION AND ORIENTATION ON THE MOLECULAR MOTION IN POLYETHYLENE TEREPHTHALATE FIBRE

The dynamic mechanical properties of polyethylene terephthalate (PET) monofilament samples with different crystallinity and draw ratio were determined over 100 to 430°K using the vibrating reed method. In this temperature range two internal friction peaks were observed at 243°K (βc) and 354-383°K (αa). The ft and βc peaks were shown to be influenced by the variation of crystallinity. From the view point of Takayanagi's mechanical model of crystalline polymers, the βc absorption may be attributed to the local twisting motion of the molecular chains in the frozen noncrystalline phase and in the defective region within the crystalline phase, and the αa absorption to the translational motion of the segments in the noncrystalline region.The temperature of the αa peak increases with increasing draw ratio, while the βc peak remains unchanged. This suggests that the stretching of PET fibre would mainly change the interchain interactions in the noncrystalline region.Takayanagi's method of determining the crystallinity of PET samples from the loss moduli of βc and αa peaks was confirmed for the fibre samples.