Study On POSS-rGO-TiO₂ Modified Cyanate/Carbon Fibre Composite And Space Radiation Effects

Cyanate ester based composites with the advantages of high specific strength,high specific modulus,fatigue resistance and good molding process are widely used as spacecraft structural materials.With the development of spacecraft towards long life and high reliability,higher requirements have been demanded on the structural materials.Therefore,it is of great theoretical and engineering significance to develop new cyanate ester based composites with the high strength,high toughness and strong adaptability to space environments.In this thesis,POSS-rGO-Ti O₂ nano-modifiers,which have resistance to space electrons radiation and atomic oxygen radiation,were designed and synthesized by using polyhedral oligomeric silsesquioxane?POSS?,graphene?r GO?and Ti O₂.r GO-Ti O₂ nano-modifiers were firstly synthesized via a hydrothermal process from graphene oxide and tetrabutyl titanate,and then POSS-r GO-Ti O₂?PGT?nano-modifiers were obtained by a liquid phase method through mixturing r GO-Ti O₂ and POSS.The microstructure,crystal structure and chemical composition were characterized and analyzed by Transmission Electron Microscope?TEM?,X-ray Diffraction?XRD?,Fourier-transform Infrared Spectroscopy?FTIR?,and X-ray Photoelectron Spectroscopy?XPS?,respectively.The analytical results show that the Ti O₂ and POSS nanoparticles in the modifier uniformly anchor on the r GO nanosheets through physical adsorption.Meanwhile,functional groups?i.e.,-OH,-NH₂?belonging to Ti O₂ and POSS can react with carboxyl groups on r GO surfaces,which effectively inhibit the wrinkle and agglomeration of r GO nanosheets.Therefore,POSS-r GO-Ti O₂ has the advantages of large specific surface area,high surface activity and versatility.POSS-rGO-Ti O₂ modified cyanate/carbon fiber ester composites were prepared.The effects of the contents of POSS-rGO-Ti O₂ on the mechanical properties of resin castings and their composites were investigated,and the modification mechanism were proposed.With the addition of the modifier,the mechanical properties of the materials were increased firstly and then decreased,and they all reach the maximum with the addition of 3 wt%modifier.The tensile strength,flexural strength and compressive strength of the modified resin castings were increased by 32%,30%and42%,respectively,compared with those without modificatiton.The tensile strength,flexural strength and interlaminar shear strength of the modified composites were increased by 6%,20%and 7%in comparison to those before modification.As the active groups on the surfaces of Ti O₂,r GO and POSS could react with each other,and as well chemically bond to the active groups on the surfaces of cyanate ester resin and carbon fiber,a strong and stable cross-linked network structure is formed,not only improving the crosslinking density of the resin matrix but also enhancing the interfacial properties of the composites.As a result,the mechanical properties of the resin castings and their composites were notably improved due to effectively transferred stress.The effects of the space electron radiation fluences and energy on the mass loss,mechanical properties and dimensional stability of the cyanate ester resin castings and their composites before and after modification were studied under a simulated space electron radiation using a space environment effect ground simulator.The results show that POSS-r GO-Ti O₂ was superior to Ti O₂ and r GO-Ti O₂ nano-modifiers in terms of enhancing the toughening effect and anti-space electron radiation damage on the resin castings and their composites.The radiation fluences have influences on the mechanical properties of the materials.With the increase of the radiation fluences,the mechanical properties of the materials were increased gradually,and then decreased after the fluence of 1.0×10¹⁶e/cm²,which may be due to the simultaneous crosslinking reaction and degradation reaction under the electron radiation.When the radiation fluences is low,the cross-linking reaction is dominant.When the radiation fluences is high,the degradation reaction is dominant.The microscopic morphology and chemical composition of the surfaces and interfaces of the materials were characterized by scanning electron microscope?SEM?,atomic force microscope?AFM?,FTIR and XPS.The trajectory of electrons inside the materials was simulated by Casino software.The anti-electron radiation damage mechanism of POSS-r GO-Ti O₂ was discussed.It is found that POSS and Ti O₂ nanoparticles can partially absorb the energy of the incident electrons,and change their traveling direction,reducing the damage to the materials.The extended r GO nanosheets can construct a large-area conductive network to form conductive pathways.Therefore,the discharge ablation on materials was alleviated,and thus anti-electronic damage performance of POSS-r GO-Ti O₂ modified resin castings and their composite were improved.The effects of atomic oxygen radiation fluences on the mass loss and mechanical properties and dimensional stability of the cyanate ester resin castings and their composite before and after modification were studied.With the increase of atomic oxygen radiation fluences,the mass loss rate of the materials was gradually increased and the mechanical properties were decreased gradually.The POSS-r GO-Ti O₂ modified resin castings and their composites had the lowest mass loss rate,the highest mechanical properties and the smallest change rate.These results show that the reinforcing and toughening effects and atomic oxygen resistance of POSS-r GO-Ti O₂on cyanate ester resin castings and their composites are superior to those of r GO-Ti O₂and Ti O₂.The microscopic morphology and chemical composition of the surface and interface of material were characterized by SEM,AFM,FTIR and XPS.The mechanism of atomic oxygen resistance of POSS-r GO-Ti O₂ was discussed.It is found that Ti O₂ nanoparticles block the invasion of atomic oxygen and change the direction of its travel.The extended r GO nanosheets provide physical barrier to block the intrusion of the atomic oxygen into the material.POSS is converted into Si O₂passivation layer under the action of high energy atomic oxygen,which effectively blocks the infiltration and erosion of atomic oxygen into the materials,and plays a role in self-repairing.Together with the synergistic effects of three components,POSS-r GO-Ti O₂ modifier effectively prevent the erosion of atomic oxygen.