Studies On Photo-crosslinking Of Ethylene-propylene-diene Rubbers/Inorganic Fillers Blends And Its Flame Retardant Materials

This paper consists of two parts: firstly, photoinitiated crosslinking of ethylene-propylene-diene terpolymer (EPDM) blends filled with calcium carbonate, talc, and calcined kaolin (CK) in the presence of benzil dimethyl ketal (BDK) as photoinitiator and trimethylolpropane triacrylate (TMPTA) as crosslinker and related properties have been studied. The results show that the EPDM blend samples with a thickness of 1-2 mm can be photocrosslinked to gel content of above 60 % by 5 s UV-irradiation. The final gel content and crosslinking efficiency are in the order of EPDM/CaCO3>EPDM/talc>EPDM/CK. The data from thermogravimetric analysis, dynamic mechanical thermal analysis and electrical properties show that UV irradiation crosslinking apparently enhances the thermal stability, storage modulus, glass transition temperature and electrical properties of EPDM blends. The data from scanning electron microscopy and mechanical tests show that the blend samples irradiated for 5s show smoother tensile fracture surfaces and an about 20-50% increase in tensile strength than unirradiated samples. Although the attenuated total-reflection FTIR data show that inorganic fillers can promote the surface photo-oxidation of EPDM blends, the above related properties of the photocrosslinked EPDM blends are enough to satisfy for many applications in the cable industry.Secondly, the EPDM/ATH/silicon blends have been photocrosslinked by UV irradiation in the presence of BDK as photoinitiator and TMPTA as crosslinker. The related physical and dynamic flammability properties have been studied by heat extension test, limiting oxygen index, thermogravitric analysis, mechanical properties and cone colorimeter tests. The results show that the photocrosslinked EPDM/ATH/silicon samples have better electrical properties and mechanical properties than unphotocrosslinked samples, but the corresponding LOI values decrease about 2% after UV irradiation. The cone colorimeter tests show that the EPDM/ATH/nano-SiO2 sample has lower HRR, MLR, THR, and EHC values than other two EPDM blend samples, which indicates that nano-SiO2 shows the best synergistic effect among the three silicon additives. The present study provides the appilication foundation for developping the photo-crosslinked and halogen-free flame retardant EPDM materials of wires and cables.