Covalent functionalization of aramid fibers with zinc oxide nano-interphase for improved UV resistance and interfacial strength in composites

Improving the resistances of organic high-performance fibers to harsh environments and enhancing the interfacial interactions of fiber-reinforced composites have become crucial in various applications. In this report, ZnO nanoparticles (NPs) and ZnO nanowires (NWs) were successfully “ grown ” on the surfaces of aramid fibers (AFs) by grafting with γ-aminopropyl triethoxysilane (KH550) followed by the growth of nano-ZnO. The surface functionalized AFs exhibited improved UV-resistances. After 168 h of ultraviolet exposure, the tensile retention rates of the ZnO-NP- and ZnO-NW-grafted AFs reached 95.6% and 97.7%, respectively, which were significantly higher than the value of 79.1% of the bare fiber. Meanwhile, the introduction of the KH500 and ZnO formed a nano-interphase, enhancing the interfacial strength of the fiber-reinforced epoxy resin composites . The interfacial shear strengths (IFSSs) of the composites with AF-g-ZnO NPs and AF-g-ZnO NWs were 42.9 and 47.8 MPa, respectively, whereas that of bare AF-reinforced epoxy resin was only 31.2 MPa. Nano-ZnO was physically deposited on the AF surfaces without KH550. The IFSS was 36.4 MPa for the AF-ZnO NP and 38.8 MPa for the AF-ZnO NW, which were lower than those of the grafted composites. Therefore, the chemical grafting nano-ZnO on high-performance fibers provides a new strategy for improving the UV-resistances of advanced fibers and to enhance the mechanical properties of fiber-reinforced composites.