Study On Surface Modification Of PBO Fibers And Their Low Dielectric Composites

Poly(p-phenylene-2,6-benzobisoxazole)(PBO)fiber possess outstanding dielectric properties,prominent mechanical properties,and outstanding heat resistance,which make it an ideal reinforcement in wave-transparent composites for aerospace applications.However,its poor UV resistance and interfacial properties seriously restrict the application and development of PBO fiber and its composites.In this study,a simple but effective surface modification method was proposed to synergistically improve the ultraviolet resistance and interfacial adhesion of PBO fibers and their composites,and the NDI-PBO fibers were prepared.To further improve the dielectric properties of resin matrix,the molecular structure of epoxy was designed to obtain low-dielectric epoxy resin(BREP),and finally the PBO fiber composite with low-dielectric and excellent performance was prepared.(1)The naphthalimide(NDI)sizing agents with different mass concentrations were prepared to modify the surface of PBO fiber.The surface physical and chemical properties of NDI-PBO fibers were studied.After compared the ultraviolet aging resistance of pristine PBO and NDI-PBO fibers,the anti-ultraviolet mechanism of NDI-PBO fibers was proposed.Compared with pristine PBO fibers,the surface roughness and surface free energy of NDI-PBO fibers were increased.After ultraviolet accelerated aging for 240h,the tensile strength and intrinsic viscosity retention rate,diameter reduction rate of NDI-PBO were still higher than that of pristine PBO fibers,and there were no macroscopic surface defects appeared,which could be ascribed to the almost undamaged chemical and crystal structures of NDI-PBO fibers.The anti-ultraviolet mechanism of NDI-PBO fibers was as follows:the ultraviolet absorption of NDI layer could reduce the intensity of ultraviolet light,which effectively alleviated the ultraviolet degradation rate and enhance the ultraviolet stability of PBO fibers.(2)The epoxy resin with low dielectric(BREP)was synthesized by Tetrabrobisphenol A epoxy resin(TBBA)and 4,4’-diphenylmethane diisocyanate(MDI),and resin systems of prepreg were prepared based on BREP.The mechanical properties,dynamic thermodynamic properties and dielectric properties of TBBA and BREP were studied.Compared with TBBA,the tensile and bending properties,the crosslinking density and heat resistance of BREP were all improved.BREP-S2 showed the best dielectric performance at 106Hz,with the dielectric constant was 3.48,10.2%higher than TBBA-S,and the dielectric loss was 0.0154,30.2%higher than TBBA-S.(3)PBO fiber composites were prepared by combining TBBA and BREP prepreg resins with pristine PBO and 2.0%NDI-PBO fibers,respectively.The interfacial bonding and dielectric properties of NDI-PBO/BREP-S2 were the best,which were significantly improved compared with others.The ILSS and TFBT of NDI-PBO/BREP-S2 were 28.61MPa and 22.12MP,respectively.The dielectric constant of NDI-PBO/BREP-S2 was 2.95 and the dielectric loss was 0.0137 at 106Hz.The interfacial and dielectric properties of PBO fiber composites were synergistically improved by NDI sizing agent and BREP resin system.