Synergistic effect of graphitic carbon nitride in enhancing flame-retardant properties of polypropylene composites

Conventional flame retardants based on polymeric materials demonstrate high flammability, producing huge amounts of smoke, toxic gases and melt drips upon burning, causing immense damage to living beings and the environment. The use of brominated organic compounds, although effective, is discouraged due to their adverse effects and ubiquitous nature. In the present study, an intumescent flame-retardant (IFR) system (g-CN@3P) is developed by compounding different amounts of g-CN as a synergist with piperazine pyrophosphate (3P) in polypropylene (PP). SEM and XPS clearly demonstrate the interaction between g-CN and 3P, leading to enhanced flame-retardant properties of 3P. An IFR containing just 1.5 g of g-CN passed the vertical burning test (UL-94) with V0 rating. High flame retardancy of the composite makes it suitable for use in applications where high flame resistance is crucial. The composition also achieved an increase in limiting oxygen index (LOI) of 21.3% compared to the composition without the g-CN synergist. Moreover, the peak heat release rate, total heat release and smoke optical density were also reduced appreciably by 62.6%, 42.6% and 17.6%, respectively. The optimum composition of PP/g-CN@3P improved the mechanical properties compared to PP/3P samples. This study emphasizes the potential of graphitic carbon nitride additives as an environmentally friendly alternative to brominated organic compounds, offering a sustainable approach to enhancing flame-retardant properties.