Circumferential Superdrawing of Hollow Poly(ethylene Terephthalate) Filaments

Amorphous poly(ethylene terephthalate) (PET) can be stretched at low tension without causing any observable crystallization at temperatures above T _g . This resultant increased length with no measurable change in orientation is called superdrawing. Superdrawing of hollow PET fibers in the circumferential direction is demonstrated in a hot water bath accompanied by increased fiber void, which is caused by a combination of air expansion and water permeation. A three-parameter model defines the kinetics of the process. The phenomenon is characterized by a rapid rise in the fiber void with a subsequent steady state. The model parameters are obtained by a simple geometric technique. The initial fiber characteristics and morphology determine the rate of void increase and the final fiber geometry. Intrinsic fiber variability is reflected in the water permeability and energy of activation. The model predicts the total residence time required in the water bath to obtain maximum void size during the superdrawing process.