| With the development of aerospace technology in recent decades,the heat resistance and thermal stability of ablative composites were required to be improved.Phenolic resin?PF?has excellent heat resistance and great manufacturability.However,the heat resistant performance of PF was still difficult to meet the requirements of the aerospace materials.In order to further improve the performance of ablative materials,it is necessary to modify PF.In this paper,nano hybrid material?SiO2-GO?was prepared by electrostatic self-assembly of graphene oxide?GO?and nanoparticles?Nano-SiO2?.Then,SiO2-RGO hybrid material was prepared by SiO2-GO chemical reduction?NaBH4?.Hybrid materials modified PF have some advantages,such as high heat resistance and strong toughness.The introduction of hybrid materials could improve the ablation and thermal properties of PF composites.In this paper,the influence of preparation methods of hybrid materials on heat resistance of PF was studied,and SiO2-GO was prepared by in-situ polymerization method,post add method,physical blending method,freeze-drying method and electrostatic self-assembly process method respectively.SiO2-GO hybrid materials were prepared by different methods could improve thermal stability and heat resistance of PF.The microstructure of SiO2-GO was characterized by SEM,TEM,FTIR and Zeta potentiometer.Most importantly,the synthetic effect of the hybrid materials prepared by electrostatic adsorption was better than that of other processes.PF was modified by doping SiO2-GO,nano-SiO2 and GO nanofillers.The TGA/DSC results show that the addition of SiO2-GO could improve the heat resistance of PF which better than that of GO and nano-SiO2 respectively.Nano-SiO2 and GO give play to synergistic effect.On the one hand,nano-SiO2 has a certain barrier effect on heat transfer,which could be dispersed evenly in PF under the help of the GO.On the other hand,the absorbed heat could be dissipated through GO layers,which could relieve the decomposition process effectively.When the amount of SiO2-GO was 2 wt.%,the initial decomposition temperature of the mass loss 5%(T5%)was 375.68?,which was increased by 65.39?than that of pure PF(T5%=310.29?);the decomposition temperature of the mass loss 10%(T10%)was 469.70?,which was increased by 62.23?than that of pure PF(T10%=407.47?);the maximum decomposition temperature(Tdmax)was 552.82?,which was increased by 23.17?than that of pure PF(Tdmax=529.65?);the thermal residual rate of SiO2-GO/PF was increased by 4.6?compared with pure PF at 800?(R800?=64.78%).The chemical structure of modified PF after curing was studied.The FTIR results show that the crosslinking density of PF could be increased by adding hybrid materials compared with pure PF,and low amount of hybrid materials could be evenly distributed in PF.SiO2-RGO was prepared by SiO2-GO chemical reduction,and the effect of SiO2-RGO on the heat resistance of PF was investigated.TGA/DSC results show that the T5%,T10%and Tdmax of 1 wt.%SiO2-RGO/PF was increased by 115.05?,76.90?and 25.15?compared with pure PF respectively,and the thermal residual rate at 800?was increased to 71.32%.It was shown that low amount of SiO2-RGO hybrids could significantly improved the thermal stability of PF and reduced the cost of industrialization.After chemical reduction,the number of GO functional groups was reduced greatly,and heat resistance was improved.The VSF/SiO2-RGO/PF composites were prepared by VSF and modified PF,and the ablation properties of composites were investigated.The oxygen-acetylene ablation experiment results show that a small amount of SiO2-RGO was introduce into PF which would help to improve the ablation resistance of VSF/SiO2-RGO/PF composites.The mass ablation rate was less than 0.17 g/s,and the line ablation was less than 0.10 mm/s.Under certain pressure,the hybrid materials would slip between the VSF fiber layers.So that the composites become compact and the size of micropores was decreased,which was beneficial to improve the ablative performance of composites. |
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