Polypyrrole/poly(p-phenylene terephthalamide) composite fibers: Morphology, mechanics, and electrical properties

Polypyrrole/poly(p-phenylene terepthalamide) (PPTA) composite fibers were fabricated by the oxidative polymerization of pyrrole within the gel structure of never-dried, dry-jet, wet-spun PPTA fibers. The composites were formed by infiltration of the swollen PPTA fibers with the chemical oxidant FeCl;The composite morphology was examined by scanning electron microscopy (SEM) and wide-angle x-ray diffraction (WAXS). SEM results demonstrated the existence of micron-sized polypyrrole inclusions in the fiber interior, as well as a polypyrrole skin on the fiber surface. As the conductive phase volume fraction was increased, the polypyrrole located in the fiber interior began to form an interconnected network. WAXS results indicate an essentially amorphous polypyrrole phase.;The tensile modulii of the composite fibers exhibited a "rule-of-mixtures" dependence upon PPTA content. The compressive properties of several composite fiber compositions were evaluated by the elastica loop method. The compressive strengths were found to be 82-151% of the corresponding ultimate tensile strengths.;The temperature dependencies of the composite fiber d.c. conductivities is reasonably well-described by the predictions of the three-dimensional variable-range hoping (3DVRH) charge transport model. Deviations from the 3DVRH law are, however, observed in the high temperature limit, as has been occasionally reported in the literature for doped polypyrroles. The temperature dependence of the composite fiber thermopower is also similar to literature measurements on doped polypyrroles. The similarity of the fiber conductivity and thermopower results to literature reports on polypyrroles indicate that the heat and electric currents in these materials are carried by a continuous polypyrrole pathway.