Synergistic effect of organo-modified montmorillonite and intumescent flame retardant on improving flame retardancy and thermal stability of polypropylene composites

It is still a great challenge to increase the efficiency of intumescent flame retardant (IFR) in polypropylene (PP) system. Here, the synergistic effects of organo-modified montmorillonite (OMMT) on flame retardancy and thermal degradation of a novel halogen-free intumescent flame retardant PP system, which was composed of the charring agent (SBCPO), ammonium polyphosphate (APP) and PP matrix, were investigated. The experimental data indicated that a small amount of OMMT (3 wt%) could significantly improve the limiting oxygen index (LOI) value of PP/IFR system to 29.5%, and the composites could pass the UL-94 V-0 rating. Meanwhile, the cone calorimeter test (CCT) results demonstrated that the peak of heat release rate (PHRR), total heat release (THR), smoke produce rate (SPR), and mass loss rate (MLR) values of PP/IFR20/OMMT3 sample was much lower than those of PP/IFR system without OMMT. According to the char structure analysis, the flame retardant mechanism was mainly contributed to the synergistic effect of OMMT and IFRs on promoting the forming more compact and continuous char layer, which increased the barrier action to heat, oxygen, and flammable gases. Furthermore, the TGA data further demonstrated that OMMT could efficiently increase the thermal stability of PP/IFR composites. Thus, this work provides a cost-efficient method to prepare high-performance PP composites and expands their applications in the field of flame retardancy required.