Ammonium polyphosphate–aluminum trihydroxide antagonism in fire retarded butadiene–styrene block copolymer

In this paper the effect of aluminum trihydroxide (Al(OH)3—ATH) on the surface protection from fire for a styrene butadiene rubber (SBR) provided by ammonium polyphosphate ([NH4PO3]n—APP) is studied. The combustion behaviour is studied by means of Cone Calorimetric tests: a maximum fire retardant effect is observed with 10–12 wt.% of APP. ATH, less effective as fire retardant, has been added at 60 wt.% to reach comparable results as measured by cone calorimetry for 12 wt.% APP. Replacement of ATH in the best performing SBR + 12 wt.% of APP shows an antagonistic effect with as little as 1 wt.% of ATH. The combustion behaviour is explained with the mechanism of interaction between SBR, APP and ATH, in which formation of aluminum phosphates negatively affects the surface protection provided by the ultraphosphate surface coating formed on heating APP in SBR.