A novel halogen-free flame-retardant fabrication for the study of smoke suppression and flame retardancy of polystyrene

A novel P–N flame-retardant (PON) was synthesized by nucleophilic substitution reaction using diphenyl phosphoryl chloride and piperazine as raw materials. Its chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR), liquid-state nuclear magnetic resonance (NMR), high resolution mass spectrometry (HEMS) and elemental analysis, and its thermal stability by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Subsequently, five char-forming agents, namely pentaerythritol (PER), chitosan (CTS), lignin (LI), graphene (GN) and expandable graphite (EG), were selected to form five intumescent flame-retardants in a 1:1 mass ratio with PON. Polystyrene (PS) composites were prepared by melt blending method. The synergistic effect of PON and different char-forming agents on thermal stability, combustion behavior and flame retardancy of PS composites were systematically investigated. The results showed that the PS/10% PON/10% EG composite had the highest limiting oxygen index (LOI) value of 25.8%, and the cone calorimetric test showed that the peak heat release rate (pHRR), total heat release rate (THR), and total smoke release (TSP) of the composite were reduced by 74.6%, 24.4% and 43.6%, respectively, compared with neat PS, and this composite exhibited the most excellent flame retardancy. Finally, the flame-retardant mechanism of PS/10% PON/10% EG composite was discussed and proposed by the results of scanning electron microscope (SEM), thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TG-IR), and pyrolysis-gas chromatography-mass (PY-GC/MS) measurements in detail.