Effects of surface‐dissolution process multivariables on the morphology, mechanical properties, and crystallization of all‐aramid composites

A new type of self‐reinforced composite based on high‐performance aramid fibers was developed to produce an “all‐aramid” composite by applying a surface‐dissolution method to fuse poly(p‐phenyleneterephthalamide) (PPTA) fibers together. After immersion in concentrated (95%) sulphuric acid (H₂SO₄) for a selected period of time, partially dissolved fiber surfaces are converted into a PPTA matrix phase. Following extraction of sulphuric acid and drying, a consolidated composite structure is formed. By examining the microstructure and mechanical properties of all‐aramid composites, it was found in our previous study that the optimal immersion time of aramid fibers in 95% sulphuric acid was 120 s. In this article, other processing variables—including initial and final coagulation, coagulation time, consolidation pressure, and time—were regulated and their effects on the morphology, mechanical properties and, crystallization of all‐aramid composites were investigated and discussed. A series of optimal surface‐dissolution processing conditions were achieved to obtain the best‐achievable microstructure and mechanical properties of all‐aramid composites. All‐aramid composites prepared with these optimum conditions possess excellent mechanical properties along the direction of orientation with tensile strength of 1.44 GPa and tensile modulus of 76.8 GPa. As fiber, matrix, and interphase in all‐aramid composites are based on the same high‐temperature‐resistant PPTA polymer, these materials have the prospective potential for high‐temperature applications. POLYM. COMPOS., 39:3307–3316, 2018. © 2017 Society of Plastics Engineers