Synergistic Effect of Silicone Macromolecular Charring Agent and Ammonium Polyphosphate on Improving Flame Retardancy and Mechanical Properties of Ethylene-Butyl Acrylate Copolymer Composites

Power cables are important pieces of equipment for energy transmission, but achieving a good balance between flame retardancy and mechanical properties of cable sheaths remains a challenge. In this work, a novel intumescent flame retardant (IFR) system containing silicone-containing macromolecular charring agent (Si-MCA) and ammonium polyphosphate (APP) was designed to synergistically improve the flame retardancy and mechanical properties of ethylene-butyl acrylate copolymer (EBA) composites. The optimal mass ratio of APP/Si-MCA was 3/1 in EBA composites (EBA/APP-Si-31), corresponding to the best flame retardancy with 31.2% of limited oxygen index (LOI), V-0 rating in UL-94 vertical burning test, and 76.4% reduction on the peak of heat release rate (PHRR) in cone calorimeter test. The enhancement mechanism was attributed to the synergistic effect of APP/Si-MCA during combustion, including the radical-trapping effect, the dilution effect of non-flammable gases, and the barrier effect of the intumescent char layer. Meanwhile, the tensile results indicated that EBA/APP-Si-31 also exhibited good mechanical properties with the addition of maleic anhydride-grafted polyethylene (PE-g-MA) as the compatibilizer. Thus, the APP/Si-MCA combination is an effective IFRs system for preparing high-performance EBA composites, and it will promote their applications as cable sheath materials.