The Effect of Phosphoric Acid Functionalization of Para-aramid Fiber on the Mechanical Property of Para-aramid Sheet

The mechanical properties of para-aramid sheet (PAS) are mainly dependent on the interfacial property between para-aramid chopped fibers and fibrids. However, the chemical inertness and smooth surface of para-aramid chopped fiber lead to the poor interfacial adhesion between para-aramid chopped fibers and fibrids. In this study, para-aramid chopped fiber was treated by phosphoric acid (PA) solution with different concentration in order to prepare PAS with high mechanical strength. It was shown that PA -treatment can increase the surface roughness and improve the surface oxygen-containing active groups of para-aramid chopped fibers. In addition, there is a critical value of PA-concentration (20%). Proper PA-treatment gives rise to an increased tensile strength of PAS from 2.41 to 3.41 kN/m by an increment of 41.49%. However, excessive PA -treatment results in a dramatic reduction of tensile strength for para-aramid fibers and also for PAS possibly due to the structure destruction of para-aramid fiber. This work shows a simple but highly-efficient approach for improving the mechanical property of PAS via PA-treatment of para-aramid chopped fibers, and simultaneously elaborating the reinforcing effects for high-performance PAS especially through optimizing the interfacial property between para-aramid chopped fibers and fibrids.