Processing of thermotropic liquid crystalline polymers and their blends

The objectives of the research included a study of melt spinning characterizations of thermotropic liquid crystalline polymers (TLCPs) and an examination of the feasibility of introducing a second TLCP as a \u27coupling agent\u27 to improve the adhesion between components in normally incompatible TLCP/thermoplastic blends. The effect of processing conditions during isothermal melt spinning of two TLCPs, a wholly aromatic copolyester KU-9211 (also named K161) and an aliphatic containing TLCP, PET/PHB60, on fiber properties were conducted. Among the processing variables studied, the draw ratio was the primary factor in determining both the fiber modulus and the molecular orientation. A composite model based on a rigid-rod rotation mechanism and the deformation of nematic domains in an elongational flow field was used to model the experimental results and was compared with other theories available in the literature. Conformance of experimental data to the composite model was obtained by using a single temperature dependent parameter n, suggesting that the rigid-rod rotation mechanism could be used to predict the orientation development of TLCPs.^ With regard to the second objective, thermotropic LCP/LCP fiber blends containing K161 and PET/PHB60 as the constituents were prepared by a combination of melt-blending and hot-drawing. Morphological evidence showed that the dispersed phase consisted primarily of highly oriented, 0.5 to 2 $\mu$m diameter rigid-rods of aromatic fibers imbedded in a matrix of predominantly aliphatic TLCP fibrils with diameters in the range of 20 to 50 nm. An interphase of approximately 50 nm strongly bonded the two phases together. It was found that the processing conditions employed for melt blending had caused PET/PHB60 to undergo chain scission, thereby creating chemical interactions between the two TLCP components during the melt blending process. Preliminary studies on ternary systems confirmed the concept of using a second TLCP phase, PET/PHB60, to improve the adhesion of binary K161/PET blends. It was also found that the adhesion between the reinforcing K161 and the matrix PET phases depended on both the absolute content of the coupling PET/PHB60 phase introduced and the relative composition of the two thermotropic LCPs.