An efficient synergistic system for simultaneously enhancing the fire retardancy, moisture resistance and electrical insulation performance of unsaturated polyester resins

Unsaturated polyester resins (UPR) are usually used in the field of electronic appliances, but their inherent flammability and hygroscopicity severely limit their wide application. In this research, dimelamine pyrophosphate (DMPY) was synthesized and constituted a synergistic flame retardant system (FRs) with aluminum diethylphosphinate (ADP). The FRs was applied to flame retarded UPR thermosets and the fire retardancy, moisture resistance, mechanical properties and flame retarded mechanisms of UPR/FRs were comprehensively investigated. When as low as 15 wt% FRs was incorporated, UPR/FRs achieved UL-94 V-0 rating during vertical burning tests and the limiting oxygen index value reached 27.9%. FRs stimulated UPR matrix to form uniform, stiff and dense char layer on materials surface during combustion process. Besides, the phosphine and phosphine oxygen radicals and inert gases generated from FRs exerted the inhibition and dilution effect in gas phase. Thus, the heat release and effective heat combustion of UPR/FRs were conspicuously suppressed. Moreover, UPR/FRs retained satisfactory flame retardancy and mechanical performance after water resistance tests. The moisture resistance of UPR/FRs was evidently enhanced compared with UPR and it led to the maintenance of electrical insulation properties of water treated UPR/FRs. Overall, the superior fire safety, moisture resistance and electrical insulation performance promised the flame retardant UPR thermosets crucial application values in the key areas. Keywords: Unsaturated polyester resins, Synergistic flame retardant system, Fire safety, Moisture resistance, Electrical insulation performance