Effects of Fiber Modification on the Mechanical Properties of Solution-Cast Poly(vinyl chloride) Films Reinforced by Aramid Fibers

This study compared the effectiveness of three fiber treatment methods for reinforcing polyvinyl chloride (PVC) with aramid fibers. Two of them used phosphoric and nitric acids, respectively, the latter of which was introduced for the first time. Acid etching roughens the fiber surface for increased friction and mechanical interlocking with PVC. The third approach treated fibers with a dimethyl sulfoxide (DMSO)/potassium hydroxide (KOH) deprotonation procedure. A more streamlined procedure was introduced in this study which omitted alkyl functionalization in favor of ethanol precipitation. Deprotonation disrupts the crystalline structure in the fibers and unbundle them into aramid nanofibers (ANFs). All treatment procedures lead to substantial improvements in composite mechanical properties. Compared with phosphorous acid, treatment by nitric acid results in higher tensile strength and Young’s modulus. Composites with ANFs show highest tensile strength among all cases. Fractography reveals distinct failure mechanisms between composites with acid-treated fibers versus those with ANFs. The acid-treated fibers exhibit interfacial delamination during material failure, indicating that enhanced composite strength is mainly attributed to stronger interfacial forces. In contrast, ANFs do not carry load in the same way as the original fibers do, but their smaller dimensions allow nanoscale dispersion, which can suppress microcrack formation during deformation. Our systematic evaluation of fiber treatment options provides critical insights for tailoring fiber-matrix interactions in non-reactive thermoplastic systems, advancing the application potential of flexible PVC in load-bearing environments.