Extending Service Life and Detecting Degradation of Poly(p-phenylene-2,6-benzobisoxazole) (PBO) Fiber

Poly(p-phenylene-2,6-benzobisoxazole) (PBO) fiber has a high strength, a high modulus, and is light weight, which makes it a leading candidate for soft body armor and fiber reinforced plastic composites. The use of PBO fiber in protective applications is limited by its mechanical degradation during service. Battelle has developed a supercritical (sc)CO2 chemical diffusion post processing method to treat PBO fiber that decreases the rate of mechanical properties degradation and increases its useable service life. The tensile data show that this treatment yields a 14 % increase for tenacity over untreated fibers after 120 days of accelerated aging (70 oC, 90 %RH) when using 3- glycidoxypropyldimethoxymethylsilane (GPDMS) epoxy silane as the chemical infused into PBO fibers. The epoxy silane chosen demonstrated an incremental increase in fiber life; with optimization, greater gains could be realized. Additionally, fluorescent spectroscopy was performed on methanol rinses of aged PBO fibers as an analytical method for determining extent of fiber degradation. Initial testing has indicated that the intensity of fluorescence peak emission have a correlation to the degradation level of the PBO fiber. There is potential for an analytical technique to be developed to test fibers from deployed soft armor to determine if the material still possesses ballistic protection, or if it should be removed from service.