Preparation And Tribological Properties Of Carbon Fiber Reinforced Polyimide Composites

Carbon fiber-reinforced polymer composites had been widely applied in aerospace,aerospace,machinery,transportation and other fields due to the properties of low density,high specific strength and specific modulus,good chemical stability,and excellent tribological property,including gears,bearings,and other friction components.However,the surface of the carbon fiber was inert,the surface energy was low,and the interface adhesion was poor when it was composited with the polymer matrix,which greatly limited the applications of the carbon fiber-reinforced polymer composite material.In this paper,carbon fiber-reinforced polyimide composites?CF/PI?were used as the research object,and nanomaterials?eg.silica nanoparticles?SiO₂?,carbon nanotubes?CNTs?,and molybdenum disulfide?MoS₂??were introduced into the surface of the carbon fiber by control.In order to improve the interface between CF and PI,improve the tribological properties of the composite,and study its enhancement mechanism in detail.The specific research content and achievements are as follows:?1?In-situ synthesis of SiO₂ nanoparticles on the surface of CF by sol-gel method,carbon fiber-silica hybrid material?CF-SiO₂?was prepared and the SiO₂nanoparticles were introduced into the CF/PI composite interface.We had studied its effect on the thermal stability,mechanical properties and tribological properties of the composites.The results showed that the T_-5wt.%?corresponding temperature at 5%mass loss?of the CF-SiO₂/PI composite increased from 328.6°C to 499.2°C,and the composite hardness and elastic modulus also increased by 22%and 12.2%respectively,compared to the pure polyimide.Because of the growth of SiO₂nanoparticles on the surface of CF had increased the roughness and activities of the CF surface,improved the interface between CF and PI,and were more conducive to stress transmission and dispersion during friction and wear.These were reasons contributed to the composite material had a lower coefficient of friction and wear rate.?2?A multi-scale carbon fiber-carbon nanotube?CF-CNT?hybrid was fabricated by means of polyamide-amine macromolecules?PAMAM?via chemical grafting method,and then the corresponding polyimide?PI?composites were prepared using hot pressing technique.The microstructure and chemical composition of the CF-CNT hybrid were characterized,and its enhancement mechanisms on the tribological properties of PI were investigated systematically.Results showed that the CF-CNT hybrid had many functional groups and increased roughness,which was good for ameliorating the interfacial combination between the CF and PI matrix,further indicating that the PI/CF-CNT composite possesses excellent friction and wear properties.The friction coefficient and wear rate of the PI/CF-CNT composite were0.213 and 1.79×10^-6mm³/Nm,i.e.,a decrease of 22 and 72%compared to pure PI,respectively.This is because good interface adhesion of CF and PI can effectively promote stress transmission during friction and wear.More importantly,CNT onto a CF-CNT hybrid surface could stretch into the PI matrix,which not only had a reinforcing effect on the PI matrix but also can avoid stress concentration in CF,so that the composite material maintains good tribological performance during the friction and wear process,even under high load or sliding rate.?3?MoS₂ was synthesized in-situ on the surface of CF by a simple and mild hydrothermal method,and CF-MoS₂/PI composites were prepared by hot-press sintering.The microstructure of MoS₂ nanosheets on the surface of CF and the effect on the tribological properties of the composites were systematically studied.The results showed that MoS₂ nanosheets decorated onto the surface of CF increased the interfacial adhesion between CF and the PI matrix.This enhanced the hardness and thermal stability,and was also favorable for transferring stress from the matrix to CF during friction and wear process.More importantly,MoS₂ nanosheets could be released to the wear surface and played a good role in self-lubricating,giving PI composites good anti-friction and anti-wear properties.