Analysis of thermoplastic polyimide + polymer liquid crystal blends

Thermoplastic polyimides (TPIs) exhibit high glass transition temperatures (T{dollar}sb{lcub}rm g{rcub}{dollar}s), which make them useful in high performance applications. Amorphous and semicrystalline TPIs show sub-T{dollar}sb{lcub}rm g{rcub}{dollar} relaxations, which can aid in improving strength characteristics through energy absorption. The {dollar}alpha{dollar} relaxation of both types of TPIs indicates a cooperative nature. The semicrystalline TPI shows thermo-irreversible cold crystallization phenomenon. The polymer liquid crystal (PLC) used in the blends is thermotropic and with longitudinal molecular structure. The small heat capacity change ({dollar}rmDelta Csb{lcub}p{rcub}{dollar}) associated with the glass transition indicates the PLC to be rigid rod in nature. The PLC shows a small endotherm associated with the melting. The addition of PLC to the semicrystalline TPI does not significantly affect the T{dollar}sb{lcub}rm g{rcub}{dollar} or the melting point (T{dollar}sb{lcub}rm m{rcub}{dollar}). The cold crystallization temperature (T{dollar}sb{lcub}rm c{rcub}{dollar}) increases with the addition of the PLC, indicating channeling phenomenon. The addition of PLC also causes a negative deviation of the {dollar}rmDelta Csb{lcub}p{rcub}{dollar}, which is another evidence for channeling. The TPI, PLC and their blends show high thermal stability. The semicrystalline TPI absorbs moisture; this effect decreases with the addition of the PLC. The absorbed moisture does not show any effect on the degradation. The addition of PLC beyond 30 wt.% does not result in an improvement of properties. The amorphous TPI + PLC blends also show the negative deviation of {dollar}rmDelta Csb{lcub}p{rcub}{dollar} from linearity with composition. The addition of PLC causes a decrease in the thermal conductivity in the transverse direction to the PLC orientation. The thermomechanical analysis indicates isotropic expansivity for the amorphous TPI and a small anisotropy for the semicrystalline TPI. The PLC shows large anisotropy in expansivity. Even 5 wt.% concentration of PLC in the blend induces considerable anisotropy in the expansivity. Thus, blends show controllable expansivity through PLC concentration. Amorphous TPI + PLC blends also show excellent film formability. The amorphous TPI blends show good potential for applications requiring high thermal stability, controlled expansivity and good film formability.