A Method of Forming Composite Structures Using In Situ-Formed Liquid Crystal Polymer Fibers in a Thermoplastic Matrix

A new high speed and potentially economical method of creating a composite material and structures therefrom is tested. The method consists of spinning composite fibers from a melt blend of a thermoplastic with a liquid crystal polymer (LCP). Discontinuous fibrils of the LCP are formed in situ during the spinning process. These composite fibers are aligned and placed in a mold and heated to melt the thermoplastic matrix, but not the fibrils. A finished composite structure reinforced by the LCP fibrils is obtained when the thermoplastic phase is consequently consolidated. Our experiments show the proposed process is reasonable for an easily processed polystyrene matrix. High modulus fibrils with essentially infinite L/D ratios are readily produced in the extrusion process using 40 wt% of a wholly aromatic poly(ester-co-amide) LCP from Celanese. The integrity and alignment of the LCP fibrils is retained in the molding step. Mechanical tests show that the fibers produced by high shear rate processing have a stiffness approaching 23 GPa and match an axial rule-of-mixtures theory. The use of polystyrene resulted in brittleness. Molded composite plates exhibit slightly lower stiffness and significantly lower strength than individual fibers.