Influence of Supercritical Carbon Dioxide-Assisted Polyamide Acid Modification of Aramid Fibers on the Properties of Aramid Fiber-Reinforced Styrene Butadiene Rubber

Abstract

Modified aramid fibers (AFs) were prepared through grafting modification of polyamide acid (PAA) assisted by supercritical carbon dioxide (scCO₂). The scCO₂-assisted diffusion, penetration, and grafting reaction of PAA not only enhanced the graft rate but also produced a uniformly grafted layer on the modified fibers. After scCO₂-assisted grafting with 5 wt% PAA, the grafted amount was 10.23%, the surface crystal spacing increased, and the crystallinity increased by 8.64%. Moreover, the tensile strength of the uniformly layered fibers increased by 9.66%. Next, short modified AF-reinforced carbon black/styrene butadiene rubber (SBR) was prepared with an AF/CB/SBR ratio of 2/50/100 parts per hundred rubber. As an acidic substance in the grafted coating layer, PAA was found to delay the vulcanization process and increase the positive vulcanization time. After modification with scCO₂-assisted 5 wt% PAA, the –COOH groups in the grafted layer participated in the curing process of the curing agent. The rough and uniformly grafted layer enhanced the dispersibility of the modified fibers through the SBR matrix. The modification increased the tensile strength and modulus at 100% of the composites by 16.01 and 32.47% and accordingly improved the cutting resistance.