Material BehaviourImprovement of environmental stress cracking resistance of polycarbonate by silicone coating

To explore the possibility of using surface coating to reduce environmental stress cracking (ESC) of transparent polycarbonate (PC) parts, silicone coated and SiO2 coated PC were tested in a self-made three-point bending apparatus in the presence of ethanol. The variation of stress with time was recorded, and the surface cracking was observed to evaluate the ESC resistance of samples. Slower stress relaxation rates and fewer surface cracks indicated that silicone coating improved the ESC resistance of PC, but SiO2 coated PC was found to be no better than that of uncoated PC. Silicone coating reduced the absorption of ethanol in PC, weakening the surface plasticization, thus hindering the formation and development of cracks in PC. Nanoindentation test results showed that the mechanical properties such as hardness and elastic modulus of silicone coating are a better match for PC than SiO2 coating. This allows the silicone coating to have a favorable effect in providing continuous protection for PC under the combined action of ethanol and stress.