The Thermal Shrinkage of an Oriented Polyester Yarn as a Function of Time, Temperature, and Stress

Measurements have been made with a linear variable-displacement transducer of the thermal shrinkage of an oriented polyester yarn in dry nitrogen as a function of time, temperature, and stress. The shrinkage of this material has been found to be nonlinear with respect to these three variables. A modified form of the Tobolsky and Eyring creep-rate equation has been found to describe the temperature and stress dependence. The activation energy for the process has been estimated to be 55.6 kcal/mole and the displacement volume to be 810 Å 3 . Interpretation of these experimental results appears to support a recently proposed model that thermal shrinkage of oriented semicrystalline polymers is a reflection of a structural transformation between extended-chain and folded-chain crystallites.