Zinc stannate interactions with flame retardants in polyamides; Part 1: Synergies with organobromine-containing flame retardants in polyamides 6 (PA6) and 6.6 (PA6.6)

This paper extends previous work which has shown that zinc stannate is an effective alternative synergist to antimony III oxide with brominated flame retardants in a number of polymers including polyamide 6 with the added advantage of smoke suppression. Here we report the behaviour of zinc stannate (ZS) in the presence of a number of organobromine-containing flame retardants (BrFR), including polymeric examples, in both polyamides 6 (PA6) and 6.6 (PA6.6). In PA6, bromine concentrations were fixed at either 10 or 15 wt% and bromine/tin (Br:Sn) molar ratios were varied from 2:1 to 4:1. Limiting oxygen index measurements enabled synergistic effectivity, E-s values to be calculated and related to Br:Sn ratios. The flame retardant characteristics and smoke levels of selected samples were determined by UL94 and cone calorimetric testing where appropriate. In PA6 the exact mechanisms of ZS-BrFR interactions differ for each flame retardant and suggest that for polymeric BrFR/ZS combinations optimal molar ratios are Br:Sn = 2:1. Thus it is likely that the intermediate formations of tin II and tin IV bromides are significant but that their relative importance depends on the BrFR present. In PA6.6 E-s values are also calculated and comparisons with antimony III oxide show that zinc stannate reduces the peak heat release rate by a factor of more than 2 and smoke suppression by up to 10 times at the same bromine concentration. General conclusions again demonstrate the superior overall synergistic effectiveness and smoke suppressing properties of zinc stannate with respect to antimony III oxide in both PA6 and PA6.6. (c) 2012 Elsevier Ltd. All rights reserved.