Study On PBO Fiber Modified By Benzoxazine Resin And Its Propertie

PBO fiber was a reinforced material developed by aerodynamics researchers of the US Air Force for the aerospace industry in the 1970s and 1980s.It was known as the "super fiber of the 21th century" for its "ultra-high flame retardant properties","ultra-high modulus","ultrahigh strength" and "ultra-high flame retardancy".In order to met the needs of the development of social industry and national defense industry,and accelerate the application and demonstration of new materials,the Ministry of Industry and Information Technology of China wrote high-performance PBO fiber into the "key New Materials first batch Application demonstration guidance Catalog(2019 Edition)" in 2019,which marked that high-performance PBO fiber had officially become a part of the national key strategic materials policy.However,PBO fiber was easy to be photoaged and degraded under UV light,while the surface of PBO fiber was smooth and had no active groups,which led to poor interface binding ability between PBO fiber and resin matrix,which limited the application of PBO fiber to some extent.In order to solve the problem of easy UV aging of PBO fiber,according to the easy design of the molecular structure of benzoxazine,the benzoxazine resin with UV absorption function was designed and prepared,and the anti-UV aging coating was prepared by graft coating technology and layer-by-layer assembly technology.Then the prepared benzoxazine was characterized and the properties of the modified PBO fiber were investigated.Taking advantage of the easy design of the molecular structure of benzoxazine,benzophenone benzoxazine monomer was prepared by Mannich reaction using silane coupling agent 3-aminopropyltriethyl silane,light stabilizer 4pm-dihydroxybenzophenone and paraformaldehyde as raw materials.The chemical structure of benzoxazine monomer was characterized by Fourier transform infrared spectroscopy(FT-IR)and nuclear magnetic resonance spectroscopy(1H-NMR).The curing characteristics of benzoxazine monomers were studied by differential scanning calorimetry(DSC).The ultraviolet absorption capacity of benzoxazine was analyzed by UV-vis spectrum.The results showed that benzophenone benzoxazine began to solidify at about 175 ℃.Polybenzoxazine has higher decomposition temperature and residual carbon rate,and the residual carbon rate is 54%at 800 ℃.Polybenzoxazine has the same ultraviolet absorption ability as light stabilizer 4,4’dihydroxybenzophenone.Because the surface of PBO fiber was inert and didn’t have any active groups,the surface of PBO fiber was activated by low temperature plasma technology,and then benzoxazine was successfully grafted on the surface of PBO fiber to obtain PBO fiber completely coated with benzoxazine.The accelerated UV aging test showed that although the mechanical properties of PBO fiber decreased in "L" shape before and after modification,the PBO fiber coated with benzoxazine had better UV aging resistance.Under the same conditions,compared with the original PBO fiber,the breaking strength of the fiber irradiated with ultraviolet light for 300 h was 30.16 cN,and the breaking strength retention rate was increased by 21%.In addition,the compatibility of modified PBO fiber with resin was greatly improved,from 20.31 MPa to 31.44 MPa,an increase of 54.8%.At the same time,polybenzoxazine with low surface energy endows PBO fiber with "petal effect",which can well fix deionized water droplets,and has a great application prospect in droplet transport and self-cleaning.Combined with the excellent UV resistance of benzoxazine,using silane coupling agent 3-aminopropyltrimethoxysilane as a bridge,nano-TiO2,with excellent UV shielding properties was introduced into the surface of PBO fiber to prepare PBO/(TiO2/PBa)fiber by layer-by-layer assembly technology.The modified PBO fiber also has good interfacial bonding properties with the resin,and the IFSS value of the modified PBO fiber is increased by 43.5%.At the same time,UV aging experiments show that under the same conditions,the breaking strength of PBO/(TiO2/PBa)fiber is 38.12 cN under the same conditions,which is 38%higher than that of PBO fiber.