Novel phosphorous-nitrogen intumescent flame retardant system. Its effects on flame retardancy and thermal properties of polypropylene

This paper describes the effectiveness of novel phosphorous–nitrogen intumescent flame retardant system (ammonium polyphosphate 202 and PPM Triazine HF – trademark, abbrev. IS) on fire retardancy and thermal stability properties of polypropylene (abbrev. PP) at incorporation level below the standard amount required for intumescent flame retardant system. UL-94 vertical burning test revealed that the addition of 20 wt.% of IS into neat PP is enough to reach V-0 rating (short burn without dripping). Further, a higher increase of the oxygen concentration for ignition was also found with the addition of the novel intumescent flame retardant to neat PP; LOI value of neat PP by addition of 20 wt.% IS rose from 19 to 31 vol.%. Finally, a remarkable decrease of peak heat release rate (PHRR: −91%), total heat release (THR: −42%), average of mass loss rate (AMLR: −92%), average of specific extinction aria (ASEA: −48%) and total smoke release (TSR: −58%) was revealed with increasing in IS content. Novel intumescent flame retardant system showed good flame retardancy performance pointing out that the intumescent char formed resists oxidation; this aspect was also confirmed by the thermogravimetry analysis. Hence, it can be pointed out that the improvement of flame retardancy imparted by the novel intumescent flame retardant system at lower concentration enables on one side a lower cost material formulation and on the other side the impact on the mechanical properties of the polymer might be lower. The thermo-oxidative data have revealed an enhancement of the thermal stability of the PP matrix by incorporation of IS (the PP/20IS composite showed a markedly increase in Tonset: 14 °C and Tmax: 64 °C).