Microparticle-aggregation effect of intumescent flame retardants on flame retardancy and toughening property of polypropylene

It is a widespread problem that loading intumescent flame retardant (IFR) into polypropylene (PP) always sacrificed the mechanical properties significantly. To develop PP composites with high flame retardancy and toughness, a new intumescent flame retardant (TAIC-IFR) with microparticle-aggregation structure was synthesized by a straightforward in-situ cemented method. Through its microparticle-aggregation effect, the TAIC-IFR enhanced the toughness and charring flame retardancy of PP composites, compared with the traditional intumescent flame retardant mixtures. The 3TAIC-24IFR/PP sample exhibited an increase in impact strength and elongation at the break by 71.8% and 233.5% respectively compared with 27IFR/PP. The cemented TAIC-IFR particles with rough surfaces and triallyl triazine triketone component enhanced the interface performance between the fillers and PP matrix. In addition, the TAIC-IFR with particulate microparticle-aggregation characteristics promoted charring reactions among different flame retardant components, thereby enhancing its char-forming flame retardant effect in PP. Specifically, 1TAIC-24IFR/PP with cemented aggregated flame retardant particles exhibited a UL 94 V-0 rating and 28.5% of limiting oxygen index (LOI), while PP with IFR mixture performed no UL 94 rating and a lower LOI. Moreover, the residue rate of 1TAIC-24IFR/PP increased to 15.9% from 0% of PP in cone calorimeter test. These results were attributed to the microparticle-aggregation effect of the acid source, carbon source, and gas source in TAIC-IFR particles, which exhibited better charring effect and barrier effect. This work provides a new idea for designing construction way of flame retardants to develop polymer materials with high flame retardancy and good toughness.