Phase behavior and mechanical properties of poly‐p‐phenylene terephthalamide/amorphous nylon molecular composites

Abstract

AbstractPoly(p‐phenylene terephthalamide) (PPTA)/amorphous nylon (AN) molecular composites were prepared from sulfuric acid solution by rapidly coagulating in distilled water. The regenerated films appear homogeneous and transparent. However, the rod‐like and flexible macromolecules are probably entrapped in a single phase during rapid coagulation, thus thermodynamically unstable and undergoing phase segregation upon thermal treatment. The miscibility between PPTA/AN was identified by a dielectric relaxation method. Phase behavior and kinetics of phase separation in PPTA/AN mixtures were thoroughly investigated by time‐resolved light scattering as well as optical microscope. A pseudo phase diagram reminiscent of a lower critical solution temperature (LCST) was established by a cloud point measurement. Several temperature‐jump experiments were undertaken from ambient to a two‐phase temperature region. The low PPTA content molecular composites were prepared by coagulating in a non‐solvent, then by compression molding below the phase separation temperatures. The 30 wt% PPTA molecular composite exhibits over three‐fold increase in tensile modulus relative to that of the neat AN, however, there is little or no improvement in the tensile strength. On the other hand, by a slight addition of AN into PPTA, the tensile and compressive failures of spun fibers may be improved.