The Effects of an Aqueous Medium on the Structure and Physical Properties of a Polyester Yarn

Abstract

The effects of an aqueous-dodecylsulfate solution buffered to pH 5 at 100°C on the structure and physical properties of an oriented semicrystalline PET yarn were measured as a function of time. Chain relaxation resulting in longitudinal shrinkage is shown to be the primary molecular event, and crystallization to be a secondary process involving the newly-relaxed amorphous chains. Four major structural events are observed: 1) longitudinal shrinkage, 2) crystallization leading to structural stabiliza tion, 3) surface stress concentration, and 4) rapid hydrolysis and decline in molecular weight following surface cracking of the fibers to relieve surface stress concentrations. Comparison of the effects of aqueous, thermal, and solvent (dimethylformamide) treatments of PET suggests that the molecular mechanisms and kinetics of aqueous and of thermally-induced changes are similar. Solvent-induced changes are to a large extent controlled by diffusion processes. Aqueous and solvent-treated PET are similar, in that there is an increase in structural "porosity" as a result of crystallization in the swollen state.

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