Carbon Fiber/boron-molybdenum Phenolic Composites Preparation And Ablation Properties

Carbon fiber-reinforced thermoplastic resins can be used under high temperature conditions due to their excellent properties,so they have become a hot spot in the research of ablation materials in the fields of aerospace,automobiles,and ships.Carbon fiber reinforced phenolic resin has the advantages of high specific strength,large specific modulus,heat resistance,and ablation resistance.However,due to the release of small molecules when the phenolic resin is cured,there are bonds that are not resistant to high temperatures,and it is difficult to graphitize,which affects the ablation performance,so it is necessary to modify the phenolic resin.The interface structure of phenolic resin and fiber is a key factor in determining whether to prepare composite materials with excellent performance.However,due to the low surface energy and surface inertness of carbon fiber,it is difficult to achieve mechanical chelation with phenolic resin and under wetting action.A chemical reaction occurs,resulting in a weaker interface effect,which affects the performance of composite materials,thereby limiting the performance of composite materials as functional materials.Interface optimization requires treatment of the surface of the carbon fiber,and it needs to be achieved by adjusting the physical and chemical properties of the surface of the carbon fiber.First,paper uses boric acid and ammonium molybdate as modifiers to modify the phenolic resin,in order to synthesize boron-molybdenum phenolic resin.Change the molar ratio of boric acid and ammonium molybdate to phenolic resin to synthesize a series of phenolic resins,and explore the effect of boric acid and ammonium molybdate content on phenolic resin.The influence of resin heat resistance and carbon residue rate.The modified phenolic resin was characterized by FTIR,NMR,curing degree,DSC,TG,etc.Experiments show that ammonium molybdate is copolymerized with Mo-O-C bonds,and boric acid is present in the modified phenolic resin(B-Mo-PR)in the form of B-O-C.Boric acid and ammonium molybdate modified phenolic resin will shorten the gel time and increase the curing temperature.Boric acid and ammonium molybdate modified phenolic resin will increase the degree of curing,heat resistance,and carbon residue rate.When the contents of boric acid and ammonium molybdate are 7%and 6%respectively,the phenolic resin modified with ammonium borate and molybdate has the highest curing degree,excellent heat resistance,and the highest carbon residue rateSecondly,using the self-aggregation and adhesion properties of dopamine,active groups were introduced on the surface of carbon fibers,and the effect of dopamine concentration on the surface properties of carbon fibers was systematically studied.Through SEM,AFM,XPS,FTIR,surface energy and other tests,the surface morphology,surface roughness,surface chemical state,and surface wettability of the carbon fiber after dopamine treatment were characterized.Dopamine treatment improves the surface roughness of carbon fiber,increases the content of active groups such as-NH₂on the surface,increases the active sites of the interface,improves the surface polarity and surface energy of carbon fiber,and improves the wettability of resin and fiber.The results show that when the concentration of dopamine is 1.5g/L,there is the smallest dynamic contact angle and the largest surface energy.Based on the above research,select unmodified phenolic resin,modified phenolic resin with 7%boric acid and 6%ammonium molybdate as the matrix,and use CF,1.5g/L dopamine treated CF as the reinforcement to synthesize a series of carbon fibers/Boron-molybdenum phenolic composite material.The mechanical properties of composite materials such as interlayer shear and three-point bending are tested,and the ablation performance of the material is tested by the oxyacetylene method to explore the mechanical properties of the composite material on the surface of carbon fiber treated with boric acid,ammonium molybdate and dopamine.Impact.SEM was used to investigate the effects of boric acid,ammonium molybdate modified phenolic resin,and dopamine on the changes in the microstructure of the composite material.