Study On Surface Modification Of PBO Fiber Based On Hierarchy

As a kind of organic polymer fiber,poly(p-phenylene benzobisoxazole)(PBO)fiber has the characteristics of low density,excellent mechanical properties,strong corrosion resistance,high temperature resistance and non-flammability.It is an ideal composites reinforcement and an important choice for material upgrading in aerospace,unmanned aerial vehicle(UAV),automotive and military fields.However,smooth surface and lacking active group great impact on the mechanical properties of PBO fiber/resin composites.It is an important method to improve the mechanical properties of PBO fiber/resin composites by modifying the fiber surface,optimizing the interfacial phase and improving the compatibility between the fiber and matrix.Various methods such as deposition and grafting and various substances such as polymers and nanoparticles were used to construct layered interfaces and customize phase structure in order to enhance the mechanical properties of PBO/resin composites.Rigid dendritic polymers with abundant amino functional groups were synthesized on the fiber surface by alternately grafting melamine and 1,3,5-benzenetricarboxylic acid chloride(TMC).The relationship between the number of melamine grafting and the interfacial properties of PBO/resin composites was studied.Dendritic polymers synthesis significantly improved the fiber surface roughness and rich amino groups can greatly improve the fiber surface energy and fiber wettability to matrix,which results in stronger mechanical interlocking and tighter interfacial bonding between the fiber and matrix,and significantly improves mechanical property such as impact property and interfacial property.Compared with the original PBO fiber(PBO-O)composites,the interfacial shear strength(IFSS),interlaminar shear strength(ILSS)and impact strength of the PBO-M2 fiber composites significantly increased by 81.49%,42.17%and 51.54%,respectively.Meanwhile,dynamic mechanical thermal analysis(DMA)showed the improvement of the storage modulus,and nanoindentation test showed that there was a modulus gradient change between PBO-M2 fiber and matrix,which was one of the important reasons for the improvement of the mechanical properties of the composites.Polydopamine(PDA)and polyethylenimine(PEI)were deposited on the fiber surface by Layer-by-layer grafting method to construct PDA/PEI interface layers.The effects of 1,3 and 5 layers of PDA/PEI polymer layers on the properties of the composites were investigated.The surface microstructure observation,chemical composition analysis and thermogravimetric analysis of the modified fibers were carried,and the influence of surface modification and properties of the fibers was studied.Moreover,the monofilament tensile test showed that the tensile strength of the fiber monofilament increased slightly with the increase of PDA/PEI layers.The introduction of multi-layer polymer interface layers significantly improved the surface roughness and surface energy of fibers,and the amino functional groups can participate in the curing and crosslinking reaction of the epoxy matrix,thus enhancing the interfacial bonding ability.The PBO-P3 fiber composites showed the best mechanical properties.Compared with PBO-O fiber composites,the IFSS,ILSS and impact strength of PBO-P3 fiber composites increased by 84,96%,79.60%and 56.65%,respectively,and the DMA storage modulus increased by 53.1%.Moreover,th e in-situ nanoindentation test showed that there is a large fiber-matrix modulus difference in PBO-O fiber composites,the gradient modulus change of PBO-P3 fiber composites was obvious from fiber to matrix due to the introduction of interfacial phase.Step-by-step grafting method was used to grafting carboxyl carbon nanotubes(CNTs)and graphene oxide(GO)onto the fiber surface.The effects of grafting CNTs,GO and CNTs/GO on the mechanical properties of PBO fiber composites were studied.The effect of grafting sequence of CNTs and GO was further studied,and the interface strengthening mechanism was further explored.The grafting of CNTs and GO made the surface of the fiber rougher and the roughness significantly increased,which made the mechanical interlocking between the fiber and the matrix stronger.In addition,the introduced carboxyl functional groups can not only make the fiber have better wettability to the resin,but also react with the epoxy matrix to form strong chemical bonds.The improvement of mechanical properties of the PBO-GO-CNTs fiber composites were the most significant.Compared with the PBO-O fiber composites,IFSS,ILSS and impact strength of PBO-GO-CNTs fiber composites increased by 86.43%,96.73%and 58.78%respectively,the DMA storage modulus increased by 69.4%.Compared with the PBO-CNTs-GO fiber,the CNTs in PBO-GO-CNTs fiber surface showed a variety of grafting morphology,especially protuberate CNTs,which formed an obvious three-dimensional structure and had more contact and bonding with the matrix,thus PBO-GO-CNTs fiber composites showed better interface properties...