Structural Design And Properties Of Polybenzoxazole High Performance Fibers

Poly(p-phenylene benzobisoxazole)(PBO),rod-like polymers with extended chain conformation,have excellent thermal oxidation stability and good hydrolysis and solvent resistance.PBO fibers have excellent tensile strength and modulus,abrasion resistance and flame retardancy.Excellent mechanical properties and thermal stability make PBO fibers a great potential application in the field of high-performance composite materials.However,due to the lack of chemically active groups in PBO,interfacial adhesion ability of PBO fiber is not good enough for practical uses,which severely limits the application of PBO in composite reinforcements.In addition,the PBO fibers have a very poor UV stability,meaning that PBO fibers rapidly degrade under UV exposure even in short time.Poly(2,5-dihydroxy-1,4-phenylpyridimidazole)(PIPD)fibers are benzoxazole high-performance fibers developed on the basis of PBO.Due to the bilateral hydrogen bond network structure between the molecular chains and a large number of polar groups of PIPD fibers,the compression strength,interface property,and UV resistance of PIPD fibers are all much better than PBO fibers.However,the research on PIPD is still immature and the mechanical strength of PIPD fiber is far lower than theoretical strength,currently.The rigidity and hydrogen bond of molecular chain structure of PIPD fibers not only give it excellent mechanical and thermodynamic properties,but also lead to low degree of orientation and poor spinning performance of PIPD.In order to enhance the photostability and interfacial properties of PBO fibers,PBO-PIPD block copolymers were prepared by introducing another rigid rod-like PIPD segments into the main chains of PBO,and PBO-PIPD copolymer fibers were prepared from the polymerization solution by dry-jet wet-spinning.The results of dynamic contact angle test revealed that wettability of PBO-PIPD fibers was significantly improved compared to that of PBO fibers.Besides,both PBO fibers and PBO-PIPD copolymer fibers were exposed to UV light to determine their photostability.The copolymer fibers exhibited much improved UV-aging resistance by showing 30% improved tensile strength retention and less surface damage in comparison with PBO fibers after 480 h UV exposure.Under the current situation of PIPD fiber's poor spinning performance and low realistic strength,PIPD-ODA composite fibers were prepared by the introduction of a third monomer,4,4'-diaminodiphenyl ether(ODA),to introduce a flexible group C-O-C structure into the PIPD molecular chain.As a result,the orientation of PIPD-ODA copolymer fibers had a certain increase,and the spinnability of the composite fibers was also significantly improved compared to the PIPD fibers.The molecular weight test showed that the molecular weight of the copolymer fibers were increased by about 6% comparied with PIPD fiber while tensile tests showed that the tensile strength and modulus of the copolymer fiber increased by 10% and 8%,respectively.In addition,both the effect of ODA addition temperature on the molecular weight of composite fibers and the influence of the spinning rate on the fiber quality were also studied.The composite fibers were characterized by FTIR,XRD,SEM,TG,XPS and tensile strength tests.