The Synergistic Effects of Expandable Graphite and Ammonium Polyphosphate on the Properties of Flame-Retardant Nitrile Butadiene Rubber

This paper, investigated the effects of expandable graphite and ammonium polyphosphate on the flame-retardant properties of nitrile butadiene rubber. Several formulations of NBR were prepared by combining different ratios of expandable graphite and ammonium polyphosphate to evaluate their synergistic flame-retardant effects. The results show that the combination of expandable graphite and ammonium polyphosphate significantly enhances the flame-retardant effects of nitrile butadiene rubber, as evidenced by improved limiting oxygen index values, horizontal burning rates decreased and passed the UL-94 V1 when the ratio of expandable graphite and ammonium polyphosphate as (2/1). Results from TGA demonstrated that the ammonium polyphosphate/expandable graphite combination could retard the degradation of rubber by promoting the formation of a compact char layer on the condensed phase surface. This char layer effectively protects the matrix from heat penetration and the diffusion of flammable gas products, resulting in better flame-retardant performance. The effect of flame retardant on the mechanical properties of nitrile butadiene rubber was also evaluated. The results showed that the mechanical properties decreased with increasing flame retardant content.