In order to meet the application requirements of polymer composite coating under high temperature conditions and promote the practical application of polymer organic composite coating in the field of high temperature protection, polyimide (PI) was selected as the resin matrix, and the heat resistance was modified and enhanced by adding nano-Si3N4. Moreover, the effects of silane coupling agent KH550 and different content of Si3N4 on the surface state and heat resistance of the coating were studied. Results showed that the glass transition temperature (Tg) of the composite coating with 10% (mass fraction) Si3N4 increased to 495 ℃, which was higher than that of pure PI coating (483 ℃). After the addition of KH550, on one hand, KH550 introduced amino functional groups on the Si3N4 surface to cross-link it with the PI molecular chain; on the other hand, KH550 directly interacted with PI molecules to enhance the viscosity of the coating, so that the dispersion of Si3N4 and the binding force of the coating and the substrate were significantly improved. Besides, the PI composite coatings with different contents of Si3N4 were prepared for comparison, and it could be found that the PI composite coating with 10% Si3N4 exhibited the optimal heat resistance and surface quality.
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