Self-extinguishing polypropylene with a mass fraction of 9% intumescent additive - A new physical way for enhancing the fire retardant efficiency

Multilayer self-reinforced polypropylene composites, fire retarded with APP based intumescent systems, were found to have surprisingly good fire retardancy. The combination of V-0 classification with excellent mechanical properties could be realized at significantly lower additive levels than expected. Modifying the structure of the composites allowed the mechanism behind the observed synergistic effect to be understood. The outstanding efficiency recorded can be explained by the beneficial physical cooperation between the expanding process caused by intumescent fire retardants and the shrinking of the reinforcing tapes. Polymer systems with these components, when exposed to heat, form a special, compact charred surface layer, which hinders the release of pyrolysis gases and where the flame retarding action of P- and N- containing compounds occurs at smaller volume, and thus at higher concentration, resulting in effective fire extinction. The observed novel synergism is promising to be efficiently utilized in the formation of cost-effective, fire retardant, self-reinforced composites.