LIQUID-CRYSTAL POLYMER-CARBON FIBER COMPOSITES - MOLECULAR-ORIENTATION

The objective of this work has been to study composite systems in which carbon fibers are dispersed in a liquid crystal polymer matrix. The fundamental point of interest here has been the interfacial response that fiber surfaces can potentially induce in self‐ordering polymers. The matrix material used was a thermotropic liquid crystal polyester synthesized in our laboratory from the monomers p‐acetoxybenzoic acid, diacetoxyhydroquinone, and pimelic acid. The aromatic‐aliphatic polymer was characterized by NMR as a chemically disordered polymer of the three structural units which exhibits a nematic phase at temperatures above 150°C. Breadline proton NMR above the solid to liquid crystal transition was used to measure the rate of magnetic alignment of molecules in the matrix and polarized optical microscopy was used to analyze interfacial zones in composite samples. Fiber surfaces were found to influence the orientation and orientational dynamics of a liquid crystal polymer matrix. This was revealed by enhanced rates of magnetic orientation in the polymer melt when carbon fibers are dispersed in the medium. Fiber surfaces were also found to stabilize nematic ordering of the polymer as the melt was heated towards complete isotropization. The phenomena discovered here may originate in the development of zones around fibers with a common molecular orientation anchored by the carbon surface. Copyright © 1990 Society of Plastics Engineers