The Research On Interfacial Functionary Mechanism And Tribological Properties Of Rare Earth Solution Modified PBO Fiber Reinforced Polyimide Composite

Poly(p-phenylene benzobisoxazole)(PBO) fiber is a rigid-rod polymer with heterocyclic groups and phenyl rings in the backbone. It exhibits outstanding mechanical properties, friction-reducing and antiwear, inflaming retarding and temperature resistant properties. As a new generation of reinforcing fiber of advanced resin matrix composites in the field of aerospace and national defense, the specific strength and specific modulus are in the first rank among all the fibers. However, the characteristics of PBO fiber, chemically inert and smooth surface, prevent efficient infiltration and chemical bonding with almost all resin matrices, which severely limit the applications in the domain of advanced composite. Therefore, the modification of PBO fibers surface, which can enhance the adhesion between PBO fiber and polymer, is of great importance to study PBO fiber reinforced resin matrix composites.In this study, according to the surface properties of PBO fiber and the special chemical characteristics of rare earth, rare earth solution(RES) surface modification method was used for the surface modification of PBO fiber to improve the interfacial bonding of PBO fiber/polyimide(PBO/PI) composite, effectively improving the mechanical properties and tribological properties of PBO composite.Firstly, RES modification treatment was used to modify PBO fibers, and PBO/PI composites are prepared. The optimum content of rare earth in RES was determined through mechanical property tests and SEM morphology analysis of fracture surface. Results show that compared with coupling agent modification treatment, RES method can improve the mechanical properties properties of PBO/PI composite effectively in normal and high ambient temperature. Moreover, in high ambient temperature, RES modified PBO/PI composites have higher retention of mechanical properties at room temperature than coupling agent modified.Secondly, X-ray photoelectron spectroscopy(XPS) and Fourier transform infrared spectroscopy(FT-IR) were used to characterize PBO fibers before and after modification treatment. Structure model of interface layer of RES modified PBO/PI composite was built, and the mechanism of fiber surface RES modification treatment was analyzed. The results show that rare earths coordination chemical reaction occurred when modified with RES, and this can increase the concentration of oxygenous polar groups of the fiber surface; When PBO fibers are compounded with PI matrix, rare earth ions can continue to react with oxygen-containing functional groups on PI molecular chain. Strong and tough structure is formed in the composite interface, so the mechanical properties of PBO/PI composite are significantly increased.Thirdly, the effects of normal load, sliding velocity and lubricating condition on tribological properties of RES modified PBO/PI composites were analyzed in normal temperature environment. Results show that the friction coefficients of composites are reduced with the increase of normal load and sliding velocity in dry sliding conditions, while the specific wear rates are all increased; The friction coefficients of composites are decreased with the increase of sliding velocity and increased with the increase of load in oil sliding conditions, while the specific wear rates are all decreased. In the same test conditions, the friction-reducing and antiwear properties of the RES modified PBO/PI composite are better than coupling agent modified.Fourthly, Tribological properties of the RES modified PBO/PI composites were investigated in 130℃ and 260℃ environment respectively. Results show that the friction coefficients of composites in 260℃ environment are lower than that in 130℃ environment, while the specific wear rates are all increased in the same normal load and sliding velocity. Compared with coupling agent modified PBO/PI composite, the friction-reducing and antiwear properties of RES modified composite are optimal in the same test conditions.Fifthly, the mechanism of the improvement in tribological properties of PBO/PI composite modified by RES was discussed. The interface of RES modified PBO/PI composite has the characteristics of high bonding strength, strong toughness and high temperature resistance. PBO fibers undertake the main load between friction interfaces during friction process, which reduce the adhesion between PI matrix and counterface. Thus the friction and wear are abated.RES modification method was used to modify the PBO fiber. The mechanism of RES modification treatment on PBO fiber is expounded. The RES modified PBO/PI composites with remarkable properties of friction-reducing and antiwear are prepared. The mechanism and change law of friction and wear were analyzed systematically in normal and high ambient temperature. The application in surface modification of organic fiber with rare earth is developed. The tribological theories of resin matrix composites reinforced with PBO fiber are also enriched and developed.