Preparation of high performance poly(ethylene terephthalate) fibers: two-stage drawing using high pressure CO2

Poly(ethylene terephthalate) fibers were drawn in CO2 (liquid) at 23 degree s C above the critical pressure followed by a second stage draw greater tha n or equal to 200 degrees C in air. We investigated the effects of first st age morphology on the second stage drawability and properties of the result ant fibers after the second stage. At 200 degrees C, the maximum achievable draw ratios (DRmax) for the CO2 treated and untreated original fibers were 12.2 and 8.2, respectively. The CO2 treated fibers had 10% higher strength and modulus values. In addition, the CO2 treated fibers showed slightly hi gher birefringence and crystallinity values. At higher draw temperatures, t he fibers had high crystallinity values (>60%). However, the amorphous chai n orientation was much lower. The high drawability of the PET drawn in CO2 can be explained by the plasticization of the polymer where CO2 aids in the disentanglement of the polymer chains during the drawing process. This CO2 morphology results in a very ductile structure compared to untreated fiber s. (C) 2000 Elsevier Science Ltd. All rights reserved.