Development of UV protective sheath for high performance fibers for high altitude applications

High performance fibers have distinguished properties such as high tensile strength, good thermal and chemical resistance, dimensional stability, lightweight, and high electrical conductivity. Due to these superior properties, high performance fibers made it to the scene of broad range of applications such as aerospace, automotive, windmill, fiber reinforced composites, high strength tethers, tendons for scientific balloon, tension structures, protective clothing, and marine. Examples of such fibers are Zylon®, Kevlar®, and Vectran®. However, the fibers lose their strength significantly upon exposure to Ultraviolet (UV) and visible light. In this research, UV protective films from extruded low density polyethylene (LDPE) loaded with different content of UV stabilizers (TiO₂ nanoparticles and White PE CC®) were investigated. To assess the degree of UV blockage of each extruded protective film, their transmittance to UV and visible (UV-VIS) light was measured. Additionally, Zylon® braids were sheathed with the protective films and the strength of the braids and yarns raveled from braids was measured before and after UV exposure for different number of days. LDPE loaded with White PE CC® and 10 % TiO₂ showed the least transmittance to UV-VIS and their yarns and braids exhibited highest strength retention after exposure to artificial UV. Strength retention of braids was higher than that of individual yarns due to weak link effect and braid structure assistant.