Study On The Photo-Stability And Modification Of Poly (P-Phenylene Benzoxazole) (PBO) Fiber

Poly(p-phenylene benzobisoxazole) (PBO) high performance fiber has been known for its outstanding tensile strength and tensile modulus, high thermal stability and excellent flame retardance. However, the relatively poor resistance to photo radiation has still limited its wider applications. In this paper, the methods for improving the photo stability of PBO fiber have been explored based on the analyzing photoageing mechanisms of PBO.Firstly, the ageing tests of PBO fiber have been carried out under the radiations of absolute sunlight, absolute UV-shielded sunlight, atmospheric sunlight and atmospheric UV-shielded sunlight, respectively. Then the mechanical properties, the intrinsic viscosity, the surface morphology, the surface chemical structure and the molecular orientation of PBO fiber were investigated before and after ageing process. The results indicated that mainly the irradiation of 400-450nm waveband would cause the degradations of PBO fiber, while the irradiation of 200-400nm waveband could accelerate the ageing process, which provided a foundation for the further anti-photoageing modification of PBO fiber.In this study, the in-situ blending of anti-UV agents has been adopted at first to improve the photo stability of PBO fiber, i.e., the photo stabilizers of UVA(0.2wt%), UVB(0.1 wt%), UVP(0.1%), compositional UVA/UVB(0.2wt%/0.1wt%) and UVA/UVP(0.2wt%/0.1wt%) have been respectively added into the polymerization dope of PBO, then the mixtures were spun into fibers via liquid crystal spinning techniques. After 312 hours’ accelerated ultraviolet ageing process, it has been found that both the intrinsic viscosities and the tensile strength retentions of modified fibers were higher than PBO fiber, for instance, the tensile strength retention of modified PBO fiber containing compositional UVA/UVP was increased from 44.17% to 72.74%. The results of ageing tests under sunlight have also identified the blending of anti-UV agents, especially the compositional ones, could improve the photo stability of PBO fiber. Moreover, the loadings of anti-UV agents were less than 0.3wt%, the polymerization and spinning of PBO fibers have been hardly influenced, and the inherent advantages of PBO fiber were also maintained.On the other hand, the surface coating of soluble polyimide (PI) with UV-shielding effect has been also adopted to protect PBO fiber from photo-irradiation. The treated fibers were then submitted to the accelerated ultraviolet ageing process and the resulting changes of mechanical property and intrinsic viscosity of PBO fibers were investigated. It has been found that the surface coating with soluble polyimide had promised a photoageing protection to some extent for PBO fiber from the fact of tensile strength retention rising from 44.17% to 54.28%. Furthermore, if adding photo stabilizers such as r-TiO2 or UVA into the coating solution, the treatments would give more effective anti-photoageing improvement to PBO fiber, for example the tensile strength retention could be increased to 66.97% and 62.07% respectively.