Study On Environmental Effect And Anti-atomic Oxygen Performance Of Surface Coatings On Polyimide

In the low earth orbit?LEO?environment,the spacecraft will go through a severe test of space environment,the material is subjected to the demage of atomic oxygen?AO?and ultraviolet radiation.Especially for atomic oxygen with strong oxidability and high flux,it would cause degradation of the spacecraft material in optical,chemical and mechanical properties,and affecting the normal operation of the spacecraft.The spacecraft would not only go through the space environment in-orbit operation,launch and return,but also sunlight exposure,temperature and,humidity change and other factors when the materials are in the process of transportation and storage on the ground environment.This paper focuses on the research of atomic oxygen protective coating and the interface effect between coating and substrate to solve the above-mentioned problems.Alkaline solution under hydrothermal condition and silane coupling agent under solvothermal condition are used to modify the surface properties of polyimide.The environmental effect test was used to evaluate the combination of PI substrate and Si O₂ coating.By exploring the failure cause of the coating,the improved preparation method is investigated.The SiO₂coating was successfully prepared on the surface of polyimide by chemical bonding method.Main research results are as follows:?1?Surface modification of polyimide by alkali solution.NaOH solution was used to modify the polyimide surface under hydrothermal process.The influence of different concentration of NaOH solution,different temperature and different hydrothermal time on the modification of polyimide substrate was investigated.The results show that the optimum hydrothermal condition is one hour treatment with 0.1mol/L NaOH solution at120???2?Environmental effect evaluation of polyimide and its coating.Several surface modification methods were used to change the surface properties of polyimide and the SiO₂ coating on the surface of polyimide prepared via sol-gel method.The erosion of environmental factors such as temperature,humidity,ultraviolet radiation and atomic oxygen on the substrate and coating of polyimide were investigated.The results show that the ability of coating resistant to environmental factors can be improved to a certain extent by using the combination of alkali solution hydrothermal process and silane coupling agent solventhermal process to modify the surface of polyimide.The SiO₂ coating on polyimide can resist to the erosion of atomic oxygen,ultraviolet irradiation,and temperature change.But environmental humidity had obvious effect on the bond strength of substrate and SiO₂ coating.?3?Study on failure causes of the coating.After alkali treatment under hydrothermal process,three kinds of silane coupling agent were used under solvothermal process to modify polyimide surface.The modification effect of samples treated with different silane coupling agent were compared.The influence of rinsing and environmental effect test were investigated to explore the failure causes of coating.The results show that modified layer was created on the surface of polyimide after treating with silane coupling agent.The modified layer was peeling off the substrate after the environmental effect test.The bonding between silane coupling agent modified layer and the substrate had direct influence on protective effect of the subsequent coating.?4?Chemical bonding method to prepare SiO₂ coating.The bonding strength of the SiO₂ sol and the modified PI surface was strengthened through the selection of the solvent for the silane coupling agent and the improvement of the preparation methods.The chemical bonding was formed.The results show that SiO₂ coating is successfully prepared on the surface of polyimide by the chemical bonding method.Wrinkled coating is prepared by the SiO₂ sol catalyzed with acid.Flat coating is prepared by the SiO₂ sol catalyzed with acid and alkali.The coating is homogeneous without apparent wrinkle or particle deposition on the surface.?5?Applications of the chemical bonding method for resistance to atomic oxygen and environmental erosion.Wrinkled SiO₂ coating is successfully prepared on the surface of polyimide by the chemical bonding method.The samples were tested with water vapour,bending,temperature alternating,and atomic oxygen irradiation.The results indicate that the wrinkled SiO₂ coating prepared by the chemical bonding method did not crack after the bending test up to thousand times and even folding test.as well as temperature alternating test.Likewise,the SiO₂ coating can significantly improve the AO resistance ability of polyimide.