STUDIES ON FIBER FORMATION OF THERMOTROPIC COPOLYESTERS

Thermotropic copolyesters PET/60 PHB and PET/80 PHB fibers are melt spun at different extrusion temperatures and at different draw-down ratios. The flow behavior of PET/60 PHB is studied at different temperatures and shear rates. The melt of (PET / 60 PHB) at temperatures above 265-degrees-C exhibit low viscosity and low activation energy of flow. The modulus and strength for both PET / 60 PHB and PET / 80 PHB fibers increase with the increase in extrusion temperature and draw-down ratio in the ranges studied. High birefringence, indicating the presence of mesophase is observed between 265 and 300-degrees-C on a hot stage polarizing microscope. X-ray diffraction patterns show that the molecular orientation increased with increasing draw-down ratio. Scanning electron microscopy of these fibers shows a well-developed highly oriented fibrillar structure. Superior mechanical performance of fibers spun at around 275-degrees-C are attributed to the presence of nematic mesophase in the polymer melt.