Chemical and physical modification of poly(p-phenylene benzobisoxazole) polymers for improving properties of the PBO fibers. I. Ultraviolet-ageing resistance of PBO fibers with naphthalene moiety in polymer chain

Abstract

In purpose of improving the poor ultraviolet-ageing resistance of poly(p-phenylene benzobisoxazole) (PBO) fiber, a series of modified PBO were synthesized in poly(phosphoric acid) (PPA) by introducing 2,6-naphthalene groups into PBO molecules. 2,6-naphthalenedicarboxylic acid (NDCA) was selected as a comonomer. It was found that there was little effect of NDCA on the molecular weight of PBO. PBO and PBO-NDCA fibers were prepared through dry-jet wet spinning. The PBO-NDCA fibers exhibited much improved UV-ageing resistance by showing less reduction in tensile strength after same amount of UV exposure, and the UV-ageing resistance increased with increasing of NDCA content. It was notable that the fiber diameter was significantly decreased in proportion to UV exposure time, which implies a kind of etching was occurred on the surface of the fibers by UV irradiation. It was also found that the degree of UV etching in fibers decreased with increasing of NDCA content. Surface morphology of the fibers before and after UV irradiation was observed using FE-SEM and AFM.