Halogen-free flame retarding NBR/GTR foams

The effectiveness of some halogen-free flame retardants (i.e. aluminium trihydroxide, red phosphorus, ammonium polyphosphate, di-melamine pyrophosphate and expandable graphite) in flame retardancy of acrylonitrile butadiene rubber (NBR)/ground tire rubber (GTR) foams, blown with azodicarbonamide has been investigated by means of cone calorimetry and limiting oxygen index tests. The GTR itself was effective to reduce flammability of NBR/GTR foams. The charring behavior and synergistic effect in flame retardancy of NBR/GTR foams filled with the flame retardants have also been considered. The results showed that the introduction of phosphorus compound and expandable graphite into the foam containing aluminium trihydroxide as a base flame retardant results in a processable and considerable flame retarding products. P and N containing flame retardant such as di-melamine pyrophosphate gave the highest flame retardancy in limiting oxygen index (LOI) test and in heat release rate of the NBR/GTR foams. The results also indicated that the P–N synergistic action was not only dependent on the component proportion of flame retardants used, but was also influenced to a great degree by the P2O5/N ratios.