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 degrees C above the critical pressure followed by a second stage draw greater than or equal to 200 degrees C in air. We investigated the effects of first stage morphology on the second stage drawability and properties of the resultant 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 higher birefringence and crystallinity values. At higher draw temperatures, the fibers had high crystallinity values (>60%). However, the amorphous chain 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 fibers. (C) 2000 Elsevier Science Ltd. All rights reserved.