Expansion behavior with broad temperature range induced by ionic liquid to improve flame retardancy of polystyrene composite containing intumescent flame retardant

The polymeric composite undergoes a challenge of limitation on improvement of flame resistance by traditional intumescent flame retardants (IFRs) and confronts underlying compromise to mechanical property due to excessive load. Here, a ternary combination of butyltriphenylphosphonium-chelated orthoborates ionic liquid (IL) with aluminum hypophosphite and expandable graphite was employed to improve fire resistance of polystyrene (PS) and interfacial interaction. The optimized ratio of the IL in ternary composition was settled down, which the accordingly reduction on peak of heat release rate of PS composite approached to 72.5 % and 26.3 %, compared with neat PS and IL-free PS/IFRs composite. Meanwhile, the flame-retarding composite displayed self-extinguishment behavior under 13 wt% total loading. Retardation in condensed phase depends on residual char during combustion, which the ternary composition produced impressive long-size graphite worms. XRD and FTIR instrument for composite in non-isothermal condition disclose that addition of the IL broadened temperature range of expansion, achieving robust barrier formation during combustion. Furthermore, the IL evolved gaseous pyrolysis phosphorous-containing components was profiled by TG-FTIR technique, suggesting flame-retarding action in gas phase. In addition, the ternary composition endowed better mechanical property for PS in tensile test on account of alleviation between fillers and host polymer. With reinforcement of flame retardancy and mechanical property, the creation of ternary composition containing ionic liquid paves a way to rational design for IFRs system and process polymer composite with high performance.