Preparation And Characterization Of Modified Graphene Oxide/Epoxy Resin Composites

The large difference of thermal expansion coefficient between carbon fiber and resin matrix and the weakness of low strength and brittleness of resin are the main reasons for the failure of aerospace composite cryogenic fuel tank,threatening the safety of spacecraft.Therefore,it is urgent to develop matrix materials with high strength,high toughness and low coefficient of thermal expansion for composite tanks.Considering the advantages of graphene oxide（GO）such as high strength,low thermal expansion coefficient and active oxygen-containing groups on the surface,a new modified GO reinforced epoxy resin system was proposed.In the traditional GO epoxy resin system,a rigid interface with high strength is usually formed between GO and epoxy resin by grafting active groups on the surface of GO;Or a flexible interface can be formed between GO and epoxy resin by grafting flexible polymer chains on the surface of GO.The former interface has high stress transfer efficiency,which is beneficial to improve the strength of the composite system,but the improvement of its toughness is limited.The latter interface can toughen the composite system better through inelastic deformation,but the interface stress transfer efficiency is low,which is unfavorable to the improvement of the strength of the composite system.Based on this,in this study,the dispersion strengthening and flexible interface toughening theory are combined,and the composite effect,rigid and flexible inorganic nano particle dispersion strengthening flexible interface is creatively designed between GO and resin matrix,in order to realize the complementary advantages of flexible interface materials and rigid particles,so that the interface layer can be toughened by a certain amount of inelastic deformation,In addition,the dispersed particles can limit the large inelastic deformation of the flexible interface material and maintain the high stress transfer efficiency,so as to improve the strength and toughness of the graphene oxide epoxy resin composite system and reduce its coefficient of thermal expansion.In this study,two kinds of polyether ammonia（PEA）polymers D230 and D2000 with different flexibility were grafted onto GO surface by chemical grafting method,and then nano-Si O₂ particles were grafted onto polyether ammonia.Finally,the modified GO was compounded with epoxy resin to obtain f-Si O₂-D2000-GO-epoxy resin composite.Their structures and properties were compared with those of pure epoxy resin and epoxy resin reinforced by PEA-GO（D230-GO and D2000-GO）.It was found that compared with PEA-GO,f-Si O₂-PEA-GO had less agglomeration and better dispersion in epoxy resin matrix.Compared with pure epoxy resin,the tensile strength of D230-GO-epoxy resin and D2000-GO-epoxy resin composites increased by 47.25%and 37.55%respectively,and the fracture toughness increased by 22.35%and 25.88%respectively.Compared with PEA-GO-epoxy composite,f-Si O₂-PEA-GO-epoxy composite shows higher tensile strength and fracture toughness;The comprehensive strength and toughness index of f-Si O₂-D2000-GO-epoxy resin composite is better than that of f-Si O₂-D230-GO-epoxy resin composite.The mechanical properties of f-Si O₂-PEA-GO-epoxy composites are also affected by the content of nanoparticles grafted on the surface of modified GO（expressed by the mass ratio of GO:f-Si O₂）.Among these composites,the tensile strength of f-Si O₂-D2000-GO-epoxy resin matrix composite（GO:f-Si O₂=2:1）is the highest,which is75.41%higher than that of pure epoxy resin.The fracture toughness of f-Si O₂-D2000-GO-epoxy resin matrix composite（GO:f-Si O₂=3:1）is the highest,which is106%higher than that of pure epoxy resin.Compared with D2000-GO,f-Si O₂-D2000-GO can reduce the thermal expansion coefficient of resin matrix more effectively.At-180℃,the thermal expansion coefficient of f-Si O₂-D2000-GO composite is about 15.56%lower than that of D2000-GO composite and 20.93%lower than that of pure resin composite.In addition,the strengthening and toughening mechanism of modified GO on epoxy resin was also studied.The research results of this paper can promote the development of interface control technology and theory of graphene oxide resin system,provide theoretical guidance for the design and preparation of graphene oxide reinforced resin matrix composites with high strength,high toughness and low thermal expansion,and promote the application of resin matrix composites in the field of low temperature fuel tank.