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• A facile processing technique was designed to consummate the two defects of aramid fiber (AF). • Supercritical CO 2 drying was applied for inducing nondestructive coordination between the two phases. • The AF-ZnO fibers was endowed with high C O Zn bond contents due to the high grafting yields. • The mechanism of ZnO nanoparticles enhancing anti-UV and interfacial-adhesion properties of AF was studied. Constructing the nondestructively chemical linking between organic phase and inorganic particles has become a hot direction for polymeric surface modification due to the rising demand of anti-ultraviolet (UV) products. Herein, aramid fiber (AF) with coordination of ZnO was developed by a facile supercritical CO 2 (Sc-CO 2) drying technique to improve its UV resistance and interfacial-adhesion. Through adjusting the Zn2+ concentrations, the ZnO nanoparticles (NPs) with different decentralized system were synthesized and deposited to AF surface with stirring and the both were subsequently dried in Sc-CO 2 fluid for bonding. Results indicate that coordination between ZnO NPs and AF was established with the formation of C O Zn bond and the grafting yield of NPs was up to 34.23%. This ZnO-bonded fiber not only shows the greatly enhanced interfacial shear strength (IFSS) and UV resistance overcoming the two inherent defects of AF, but it was also endowed with higher mechanical and thermal performances than the original. For the AF-ZnO fibers in the optimum conditions, its IFSS was severely increased by 68.2%, compared to the pure AF, meanwhile the tensile strength retention after 216 h-UV irradiation is as high as 93.1%. Additionally, those fibers were obtained a better heat-resistant properties and mechanical properties, as the tensile strength and modulus, break elongation and energy were improved by 13.7%, 8.7%, 13.4% and 15.7%, respectively. Therefore, this research shows a fantastic success for nondestructively improving the interfacial-adhesion properties and UV resistance of AF. [ABSTRACT FROM AUTHOR]

Aramid fibers with low density and high strength, modulus, and thermal resistance are widely used in applications such as bulletproof vests and cables. However, owing to their chemical structure, they are sensitive to ultraviolet light, which degrades the fibers' useful mechanical properties. In this study, titanium dioxide (TiO2) nanoparticles were synthesized both on the aramid III fiber surface and in the interfacial space between the fibrils/microfibrils in supercritical carbon dioxide (scCO2) to improve the UV resistance of aramid fibers. The effects of scCO2 treatment pressure on the TiO2 structure, morphology, surface composition, thermal stability, photostability, and mechanical properties were investigated using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, ultraviolet–visible spectroscopy, and single-fiber test. The results show that amorphous TiO2 formed on the fiber surface and the interface between fibrils/microfibrils, and decreased the photodegradation rate of the aramid III fiber. Moreover, this modification can also improve the tensile strength via treatment at low temperature and without the use of a solvent. The simple synthesis process in scCO2, which is scalable, is used for mild modifications with a green solvent, providing a promising technique for synthesizing metal dioxide on polymers. [ABSTRACT FROM AUTHOR]

Aramid fibers (AFs) with their high Young′s modulus and tenacity are easy to degrade seriously with ultraviolet (UV) radiation that leads to reduction in their performance, causing premature failure and limiting their outdoor end use. Herein, we report a method to synthesize nano-SiO2 on AFs surfaces in supercritical carbon dioxide (Sc-CO2) to simultaneously improve their UV resistance, thermal stability, and interfacial shear strength (IFSS). The effects of different pressures (10, 12, 14, 16 MPa) on the growth of nanoparticles were investigated. The untreated and modified fibers were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It was found that the nano-SiO2-decorated fibers exhibited improvement of thermal stability and mechanical properties, and the IFSS of the nano-SiO2 modified fibers increases by up to 64% compared with the untreated fibers. After exposure to 216 h of UV radiation, the AFs-UV shows a less decrease in tensile strength, elongation to break and tensile modulus, retaining only 73%, 91%, and 85% of the pristine AFs, respectively, while those of AFs-SiO2-14MPa-UV retain 91.5%, 98%, and 95.5%. In short, this study presents a green method for growing nano-SiO2 on the surface of AFs by Sc-CO2 to enhance the thermal stability, IFSS, and UV resistance. [ABSTRACT FROM AUTHOR]