Abstract
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.
Highlights
Aramid III fiber (AF-III) has high strength, i.e., up to about 6 GPa, a modulus of up to 230 GPa, and a density of 1.44 g/cm3 ; it is widely used in many applications, such as bulletproof vests, firefighting gear components, ropes and cables, and fiber-reinforced composite applications
The crystalline phases of TiO2 were not found in the XRD curves of the modified fibers, which demonstrated that the TiO2 formed on the fibers was amorphous
The more TiO2 particles contained on the fiber surface and in the interfacial space between the fibrils/microfibrils, the lower the crystallinity of the fiber; this is related to the change of pressure
Summary
Aramid III fiber (AF-III) has high strength, i.e., up to about 6 GPa, a modulus of up to 230 GPa, and a density of 1.44 g/cm ; it is widely used in many applications, such as bulletproof vests, firefighting gear components, ropes and cables, and fiber-reinforced composite applications. Because of the highly oriented packed crystalline structure, it is difficult to incorporate UV stabilizers into the fibers This is why protecting high-performance fibers from UV is a serious challenge for material scientists and engineers. In semicrystalline polymer materials, photodegradation usually occurs in the amorphous state or in the interspace between fibrils/microfibrils, because oxygen atoms penetrate these regions, but have difficulty penetrating the crystal region [23]. If these spaces were modified, the photostability would be fundamentally improved.
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