Intumescent polypropylene in extreme fire conditions

Abstract The paper deals with intumescent polypropylene (PP) undergoing extreme fire (burn-through test heat flux higher than 100 kW/m2). purpose of this unusual approach is to explore the possibility design plastic (here PP) resisting burn-through test. A combination commercial flame retardants (ammonium polyphosphate-based compounds containing a char former; AP766 (AP) and FlameOff (FO) companies Clariant Inc) zinc borate (supplied by US Borax, ZB) or Kemgard (combination ZB molybdate supplied Huber, KZ) was incorporated in PP. Use KZ as synergists FO formulations increases dramatically time piercing (formation hole through plaque polymer at 80 s without vs. 280 s (heat flux = 116 kW/m2, propane burner) while AP does not show any benefit. Analyses residues obtained different times combustion solid state nuclear magnetic resonance (NMR) 31P, 11B 13C shows formation borophosphates creating glass reinforcing char: it acts ‘glue’ providing flexibility cohesion char.