EFFECTS OF HYDROPHOBIC COATINGS ON POLYBENZOXAZOLE FIBERS UNDER BALLISTIC LOADING

Polybenzoxazole fibers (PBO, commercially trademarked as Zylon) were once used as an alternative to ultra-high molecular weight polyethylene (UHMWPE) fibers in body armor systems. PBO fibers exhibit a high Young’s modulus, excellent thermal stability, and tensile strength (nearly twice that of Kevlar), but the physical properties severely degrade when exposed to water. Hydrophobic polymer coatings were applied to PBO fibers and studied for moisture resistance, coating durability, and ballistic performance. Instron tensile testing and a V50 assessment utilizing a light gas gun and 9.525 mm spherical chromium-steel projectiles were conducted on four different textile armor systems, including uncoated PBO weave, uncoated PBO weave exposed to water, polymer-coated PBO weave, and polymer-coated PBO weave exposed to water. Using load cells to measure uni-axial forces, combined with digital image correlation enabling measurement of both in-plane and out-of-plane fiber deflection, stress-strain measurements of the four different textile armor systems were measured and compared. Flex Seal liquid coating proved to be the most effective waterproof coating in terms of consistent hydrophobic performance, flexibility, and ease of application; however, further research is required to refine coating methods as well as collect additional data for the performance of PBO under dynamic loads.