All-aramid composites by partial fiber dissolution.

The area of self-reinforced polymer composites is one of the fastest growing areas in engineering polymers, but until now these materials have been mainly developed on the basis of thermoplastic fibers of moderate performance. In this work, we report on a new type of self-reinforced composites based on high-performance aramid fibers to produce an "all-aramid" composite by applying a surface-dissolution method to fuse poly(p-phenylene terephthalamide) (PPTA) fibers together. After immersion in concentrated (95%) sulphuric acid (H(2)SO(4)) for a selected period of time, partially dissolved fiber surfaces were converted into a PPTA interphase or matrix phase. Following extraction of H(2)SO(4) and drying, a consolidated all-aramid composite was formed. The structure, mechanical- and thermal properties of these single-polymer composites were investigated. Optimum processing conditions resulted in unidirectional composites of high reinforcement content (approximately 75 vol %) and good interfacial bonding. The all-aramid composites featured a Young's modulus of approximately 65 GPa at room temperature, and a tensile strength of 1.4 GPa, which are comparable with or exceed the corresponding values of conventional aramid/epoxy composites. However, since fiber, matrix and interphase in all-aramid composites are based on the same high-temperature resistant PPTA polymer, a high modulus of approximately 50 GPa was maintained up to 250 degrees C, demonstrating the potential of these materials for high-temperature applications.