Study On The Aging Of High Performance PBO Fiber

Poly（p-phenylene benzobisoxazole） （PBO） is one kind of aromatic heterocyclic rigid-rod polymer. PBO fiber produced via dry-jet wet-spinning technique has outstanding tensile strength and tensile modulus, high thermal stability and excellent flame retardant properties. However, PBO fiber’s poor resistance to ultraviolet radiation is a severe defect which limits the implication. Therefore, to improve the ultraviolet stability of PBO fiber is a key problem.In this thesis, a series of modified PBO polymer was obtained by co-polymerization from 4, 6 -diamino resorcinol dihydrochloride （DAR） and terephthalic acid （TPA）, with addition of ultraviolet stabilizer of different types and contents in polyphosphoric acid（PPA）. Then the modified PBO fibers were spun by dry-jet wet-spinning method. The ultraviolet stability of the modified fibers was investigated and the mechanism of ultraviolet aging degradation of PBO fiber was summarized.Modified PBO fibers were obtained through in-situ polymerization by introducing 2, 2’-（1, 2-Ethenediyldi-4, 1-phenylene） bisbenzoxazole（UVA） into the solution polymerization system of PBO. The addition of UVA increases the tensile strength retention rate of PBO fibers after UV aging. After 310 hours’ UV aging, the tensile strength retention rate of the pure PBO fiber is 44.17% and the UVA/PBO fiber containing 0.2wt% UVA is 64.84%. The addition of UVA also increases the intrinsic viscosity retention rate and improves the surface morphology after UV aging. The greater of the TM content, the higher of the UV stability of PBO fiber.Modified PBO fibers were prepared through in-situ polymerization by introducing mixed （rutile and anatase coexist） nano titanium dioxide （nano-TiO₂） into the solution polymerization system of PBO. The use of appropriate technology could achieve good dispersal of nano TiO₂ in PBO matrix. The addition of TiO₂ increases the tensile strength retention rate of PBO fibers after UV aging obviously. After 310 hours’ UV aging, the tensile strength retention rate of the pure PBO fiber is 44.17 percent, the TiO₂/PBO fiber containing 1wt% DLS is 62.26%, the TiO₂/PBO fiber containing 2wt% DLS is 48.75%, the TiO₂/PBO fiber containing 1.5wt% r- TiO₂ is 81.39%. The addition of TiO₂ also increases the intrinsic viscosity retention rate and thermal stability. The fiber containing 1.5wt% r- TiO₂ has best UV stability. The fiber containing 1wt% DLS has better UV stability than 2wt% DLS.Based on the results of tensile strength test, intrinsic viscosity test, SEM, ATR-FTIR, LAMAN and XRD, the ultraviolet aging degradation mechanism of PBO fiber is proposed. First, the C-0 bond and C-N bond on oxazole are caused to be broken. Second, the macromolecule chain of PBO breaks out. Then with some further degradation going on, the monomer, DAR（Diamino Resocinol Dihydrochloride）, is formed.