Solution processing of composite fibers containing rodlike and thermoplastic polymers

Abstract

AbstractThe solution processing and mechanical properties made from blends of the rodlike polymer poly(p‐phenylene benzobisthiazole) with either poly(ether ether ketone) or nylon 6,6 is described. The concentration dependence of the isotropic‐nematic phase transition for solutions of these polymers in methane sulfonic acid is in qualitative agreement with a theory of Flory. The mechanical properties of fibers that were wet spun from isotropic solutions of poly(ether ether ketone) and poly(p‐phenylene benzobisthiazole) are very sensitive to the concentration of the spinning solution. Fibers spun at concentrations near the isotropic‐nematic phase boundary have poor mechanical properties, resulting from phase separation during coagulation. However, when the solution concentration is significantly below the critical value, stiff and strong fibers are produced. In contrast, when nylon 6,6 is used as the thermoplastic component, the mechanical properties are good and are insensitive to the solution concentration. We attribute the solution concentration effects to two factors. The first is the difference in the solubility of poly(ether ether ketone) and nylon 6,6 in methane sulfonic acid‐water mixtures. The second is the connectivity of the nematic phase, which also depends on concentration and has a major impact on the mechanical properties of the resulting fiber.