THE DEVELOPMENT OF STRUCTURE AND MECHANICAL-PROPERTIES IN POLY(ETHYLENE-TEREPHTHALATE) FIBERS DURING HEAT-TREATMENT UNDER STRESS

The development of microstructure during the heat treatment of poly(et hylene terephthalate) fibres has been investigated. Specimens represen ting different durations (down to a few milliseconds) of isothermal tr eatment were prepared through interrupted annealing and rapid quenchin g. Characterization of the structure and properties of such specimens demonstrated that the transformation occurred in two stages. In the fi rst stage, microfibrillar crystals develop. The shrinkage behaviour of the material is set at this stage. In a second stage, the morphology transforms from fibrillar to lamellar. During this process, crystals b ecome increasingly perfect and the crystallinity increases. The stiffn ess of the fibre increases continuously through these stages.