Study On Environmental Stress Cracking Behavior And Ultraviolet Aging Resistance Of Polycarbonate Transparent Parts With Silicone Coatings

With many excellent performance, the engineering application of transparent polycarbonate(PC) is extending to Strategic fields such as high-end industrial products, aerospace and national defense. However, PC transparent parts are prone to environmental stress cracking(ESC) failure in use and aging degradation in complicated environment(UV radiation, temperature-shock, etc.), which limits its service life and safety.In recent years, surface Coating technology on PC parts has got great importance in industry and academia. The Researches were focused on improving the surface properties and adding functionality. The investigation of aging failure behavior of PC/coating system under certain circumstances can provide theoretical and experimental basis for the development of reliability protective means of coating on PC transparent parts, enhancing aging and failure resistance, which has important academic significance and engineering value.Based on ESC failure and UV aging of PC transparant parts, ESC behavior of PC/silicone coating systems under solvent-stress were studied in this paper, and ultraviolet aging resistance were further investigated. The main work includes:(1) Transparent Silicone and Silicone/Ti O2 hybrid coatings were prepared on PC injection molded parts, and the structure, optical properties and adhesion properties were characterized using AFM, SEM and UV-vis spectrum. The results showed that: Silicone coating had a relatively smooth surface improving the visible light transmission of PC products; The surface of PC with chromic acid modification was conducive to enhancing interfacial adhesion between coating and PC,which improved the adhesion properties.(2) ESC behavior of PC, PC/silicone coating system in N-butanol、ethanol and after temperature-shock were studied, and the influencing mechanism of coating to ESC were analyzed. The results showed that: Coating can improving ESC resistance of PC parts. Reflecting in two aspects: Under the same solvent-stress environment, compared with PC sample, the stress relaxation rate of samples with coatings was low, and the difference of the change in stress relaxation between PC and the coated samples was more obvious with the increaseing of initial stress; the number of surface cracks and width of PC samples with coatings was significantly smaller than that of PC.This is mainly due to the physical barrier effect of Silicone coating with a good compactability for diffusion absorption of solvent to PC, while organic coatings with good toughness were not easy to crack and peel off when stressed with PC together. So Silicone coating can delay or reduce PC in touch with solvent, weak the plasticizing effect of solvent, which not only reduced crazing induced points, also slowed the progression of cracks. After temperature-shock, the adhesion between coating and PC still maintain good, so coatings can still play a protective role to solvent media for PC, enhancing the ESC resistance of PC transparent parts undergone complex conditions aging.(3) Ultraviolet aging behavior of PC/coating system was investigated. By change in absorbance and yellow index of PC and PC/coating samples exposed to ultraviolet light, UV aging resistance of PC/coating system was evaluated. Studies have shown that: Silicone coating did not significantly reduce the light oxygen degradation rate of PC, this is because it do not absorb UV light, and has the Si-O-Si bond structure with a large free volume, oxygen can also penetrate to the the interface of PC substrate through coating; however, Ti O2 particles have the function of absorption and scattering UV, which makes Silicone/Ti O2 hybrid coating have a certain protective effect for PC parts to UV aging.