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 gamma-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.