Effect of Surface Silicone Coating on Environmental Stress Cracking Resistance of Transparent Polycarbonate Parts

Abstract

Environmental stress cracking(ESC) behavior of silicone coated polycarbonate (PC) in ethanol was studied. Stress relaxation of PC and PC/silicone coating under a combined action of ethanol and stress was measured by self-made three point bending equipment. After stress relaxation testing, crack morphology was observed by polarizing microscope. The results indicate that silicone coating is able to improve the stress cracking resistance of PC parts in ethanol. The coated PC shows slower stress relaxation rate and less number of cracks than pristine PC. It is mainly attributed to that the silicone coating can provide barrier effect to the absorption and diffusion of ethanol in PC substrate. Furthermore, the mechanical properties of flexible silicone coating matched fairly well with that of PC, so that the coating is uneasy to peel off from PC substrate during the ESC testing. The silicone coating has a favorable effect to protect PC substrate from ESC under the combined action of solvent and stress.

Keywords

• polycarbonate
• environmental stress cracking
• silicone coating
• stress relaxation