Influence of aramid fiber treatment and carbon nanotubes on the interfacial strength of polypropylene hierarchical composites

The microbond test was used to evaluate the interfacial shear strength (IFSS) of multiscale composites based on a polypropylene (PP) matrix reinforced with aramid fibers (AFs) chemically treated by two methods and coated with multiwall carbon nanotubes (MWCNTs). AFs were treated by two types of acid solutions and coated with oxidized MWCNTs. Scanning electron and atomic force microscopies were conducted to observe the failure modes and correlate the fiber roughness to the IFSS. While both acid treatments caused a small change in fiber roughness, MWCNT deposition largely increased the fiber roughness. The microbond test results indicate that the acid treated fibers exhibited slightly higher IFSS than the untreated fibers and such IFSS is even higher for AFs containing MWCNTs. For chemically treated fibers covered with MWCNTs, a rougher surface with matrix cohesive failure at the edge of the sheared droplet suggests that the IFSS improvement is mainly due to the physicochemical interactions among AF, MWCNT and PP, in addition to mechanical interlocking.