THERMAL AND MECHANICAL-BEHAVIOR OF CRYSTALLINE POLY(ETHYLENE-TEREPHTHALATE) - EFFECTS OF HIGH-TEMPERATURE ANNEALING AND TENSILE DRAWING

The melting behaviour and several mechanical properties of crystallized poly(ethylene terephthalate) have been investigated paying particular attention to the effect of thermal annealing at high temperature. Although the occurrence of a double melting peak in the differential scanning calorimetry (d.s.c.) curves of isothermally annealed samples can be undeniably ascribed to a recrystallization process during the heating scan, it is suggested that the chain-folded lamellar crystals grown at a moderate crystallization temperature undergo a morphological change into fringed-micelle crystals when submitted to a high temperature annealing. This conclusion is inferred from the striking changes of the mechanical properties of the samples which result from the annealing treatment, in conjunction with the thermal behaviour of drawn samples. This metamorphosis is attributed to ester interchange reactions which turn the chain folds of the amorphous layers into intercrystalline tie molecules at high temperature.