Research On Surface Modification And Factors Affecting Mechanical Performances Of PBO Fiber

PBO [Poly（p-phenylene benzobisoxazole）] is a kind of typical lyotropic liquid crystal macromolecule. PBO fiber is of high strength, high modulus and excellent stability to heat and oxygen because of its rod-like molecular chain conformation. It is the most excellent high performance fiber and is called "the king of fiber". It has wide application foreground in many areas, such as national defence, military affairs, aviation and spaceflight, civil high-tech. But at the same time, PBO fiber has some disadvantages, for example, it is prone to UV aging and has poor adhesion with resin.In this paper, the influences of different take-up speed, heat treatment and UV on the structure and performance of PBO fiber were researched. PBO fibers were prepared at different take-up speed using the moderate scale production line designed by ourselves. The structure and performance of the fiber were analyzed and measured. The results showed that the tensile strength of the fiber was mainly determined by the viscosity of the polymer. The tensile strength of the fiber was greatly improved with the increase of the viscosity of the polymer. The orientation degree, tensile strength and modulus of the fiber could be improved with the increase of the take-up speed in the spinning process. The homemade un-dried fiber and dried fiber were heat-treated, and it was found that after heat treatment, the former’s mechanical performances were superior to the latter. The influences of heat treatment temperature and time on the mechanical properties of PBO fiber were studied. The results showed that the strength and the modulus of PBO fibers could be increased by the heat treatment, but the break elongation of the PBO fibers was decreased. The best heat treatment conditions were of 12s to 20s at 500℃. The strength of PBO fibers could be raised by 9.6%, from 28.83cN/dtex to 31.60cN/dtex. The modulus of the fiber could be raised by 69.1%, from 646.91cN/dtex to 1093.85cN/dtex. The PBO fiber was coated by the TiO₂ sol. During the irradiation of the UV, the aging of the un-coated PBO fiber was obvious, and the mechanics performances were declined remarkably, while the influence of the UV on the mechanics performances of the coated PBO fiber was weaken and the aging speed of the fiber was slower.The coupling agent treatment for surface modification to improve the interfacial adhesion between PBO fiber and the resin was also studied. The interfacial shearing strength （IFSS） between the coupling agent-treated PBO fiber and the resin was measured through the single fiber pull-out test. The results showed that the treatment of surface through coupling agent could increase the IFSS between the PBO fibers and the resin, and the mechanical properties of PBO fiber were not declined. After coupling agent treatment, the IFSS between the un-dried PBO fiber and the resin was higher than the dried fiber. The IFSS between the same PBO fiber and the resin varied with the kind and the concentration of coupling agent.The un-dried PBO fibers which was dipped in acetone for 24h and then applied by 5% concentration of KH560 could get the highest interfacial shearing strength with the epoxy resin. The interfacial shearing strength between them could be raised by 69.4%.