Synergistic effect of ammonium polyphosphate and silicone macromolecular charring agent on improving flame retardancy and mechanical properties of ethylene-butyl acrylate copolymer composites

It is still a challenge to achieve a good balance on flame retardancy and mechanical properties of polymer/intumescent flame retardants (polymer/IFRs) composites. In this work, a novel IFR system containing ammonium polyphosphate (APP) and silicone-containing macromolecular charring agent (Si-MCA) was constructed 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), V0 rating in UL-94 test and 76.4% reduction on the peak of heat release rate (PHRR) in cone calorimeter test. The enhancement mechanism was ascribed to the synergistic effect of APP/Si-MCA during combustion, including the trapping radical effect, diluting effect of non-flammable gases, and the barrier effect of intumescent char layer. Meanwhile, tensile test indicated that EBA/APP-Si-31 also exhibited good mechanical properties with the addition of maleic anhydride-grafted polyethylene as compatibilizer. Thus, the APP/Si-MCA combination is an effective IFRs to prepare high-performance EBA composites, and will promote their applications as cable sheath materials.