Synergistic flame retardancy of ZnO with piperazine pyrophosphate/melamine polyphosphate in PP

Common ZnO particles was used to improve the flame retardancy of piperazine pyrophosphate/melamine polyphosphate (PPAP/MPP) in PP composites. 0.5 wt% ZnO exhibited an exceptional synergism by analyzing LOI determination, UL-94 test, and CCT. The LOI increased from 29.9% (no ZnO) to 32.3%. The corresponding flame-retardant rating was improved from UL-94 V-2 to V-0. Additionally, ZnO significantly inhibited the formation of the smoke and CO during the combustion process. The TGA, the component and the structure of the heated FRPP and CCT residues were studied by FTIR, EDS, SEM, Raman spectra and 31P Nuclear Magnetic Resonance, revealing that PPAP/MPP was dominant in the flame retardant process by condensed phase actions. Furthermore, ZnO obviously promoted the formation of the char layer and increased its graphitization degree. Thus, the thermal stability and the strength of the intumescent char layer were improved and then to reinforce the flame retardancy of flame retardant PP (FRPP).