Synergistic effect between piperazine pyrophosphate and melamine polyphosphate in flame retarded glass fiber reinforced polypropylene

Piperazine pyrophosphate (PAPP) combined with melamine polyphosphate(MPP) was adopted to prepare the flame retarded glass fiber reinforced polypropylene (FRGFPP) composites. The PAPP/MPP mixture with a 2:1 mass ratio achieved an optimum synergistic effect. The corresponding system (FRGFPP-4) passed the UL-94 V-0 classification (1.6 mm) and had an LOI value of 39.9%. Series of characterizations involving cone calorimeter test (CCT), thermogravimetric analysis (TGA), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectra, and thermogravimetric analyzer coupled with FTIR (TG-FTIR) were performed to investigate the synergistic mechanism. The synergism depends mainly on the strong interaction between PAPP and MPP. The interaction accelerates the formation of the high-quality char layer, which plays a dominant role in improving the flame retardancy and the thermal stability of FRGFPP-4. Additionally, flame inhibition and fuel dilution effects in the gas phase also contribute to the superior flame retardancy of FRGFPP-4. (C) 2021 Elsevier Ltd. All rights reserved.