Enhanced ultraviolet resistance of Kevlar fibers with TiO₂ films

Kevlar fiber is very sensitive to ultraviolet (UV) irradiation that can cause serious photodegradation effect on fibers such as increase in brittleness, loss of brightness, change of color and opacity, formation of surface cracks, etc. Thus the maintenance of mechanical properties is of great significance for Kevlar fibers servers long in hostile environments. In present paper, Nanostructured TiO₂ films were used to improve the ultraviolet resistance of Kevlar fibers by modified sol-gel technique. Specifically, polyethylene glycol (PEG) was added to improve the particle size distribution in TiO₂ sol, which was subsequently coated on the surface of Kevlar fibers to form thin nano-TiO₂ films. UV absorption spectrum result indicated the UV absorbance of PEG contained sol was much better than that of sol without PEG. The influence of the coating on UV-durability of Kevlar was investigated by an accelerated photo-ageing method. Results of mechanical measurement showed that after exposing to UV light for 160 h, the fibers without TiO₂ coating degraded and became powdery, whereas 37.5 percent of strength and 41.2 percent of break extension still remained for the TiO ₂ coated fibers. SEM analysis showed no significant surface morphological change on the coated fibers after the exposure, while some latitudinal crack fractures appeared on the uncoated Kevlar fibers.