Simultaneous effects of aluminum hydroxide/magnesium hydroxide and expandable graphite on flame resistance properties of nitrile butadiene rubber composites

Abstract

Aluminum hydroxide, magnesium hydroxide, and expandable graphite are commonly used as non-halogenated flame retardants known for their effectiveness and environmental safety. In this study, nitrile butadiene rubber (NBR) composites were prepared using a two-roll mill, incorporating various ratios of these flame retardants. The properties of flame retardants were evaluated using “limiting oxygen index” (LOI), UL-94 vertical and horizontal burning tests, and thermogravimetric analysis (TGA). The research examined the combined effects of expandable graphite, aluminum hydroxide, and magnesium hydroxide on the flame resistance of NBR. Results showed that incorporating all three additives significantly enhanced flame retardancy, demonstrated by increased LOI values and decreased horizontal burning rates, compared to using each additive alone. Furthermore, surface modification of aluminum and magnesium hydroxides with Si-69 silane, in combination with expandable graphite, led to improved flame resistance, achieving a UL-94 V-0 rating and an LOI exceeding 30.7 at 25 phr expandable graphite. In addition to flame retardancy, the influence of these additives on the mechanical properties of NBR was also assessed. Findings revealed a progressive reduction in mechanical strength as the flame retardant loading increased. Nevertheless, the mechanical properties remained within acceptable ranges for practical applications, indicating that the composites possess a good balance between flame retardancy and mechanical performance.

Graphical abstract

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