Combustion toxicity of fire retarded EVA

A Purser furnace has been used to investigate the combustion toxicity of ethylene-vinyl acetate copolymer (EVA) with and without fire retardants, under different fire conditions. Steady state flaming combustion has been studied at equivalence ratios 0 varying from 0.5 to 1.5 by driving the materials through the furnace at 750 degreesC. Yields of CO and CO2 for EVA containing 27% vinyl acetate, and its fire retarded composites, containing fire retardant fillers are presented. The materials contained 30% EVA and 70% hydrated aluminium oxide (ATH), or 65% ATH and 5% zinc hydroxystannate (ZS), or 5% magnesium borate (MgB) or 5% zinc borate (ZB). In each case the same mass of EVA was used in the determination. The yields of CO per g of polymer from the EVA-fire retardant composite samples showed very similar yields of CO under well ventilated conditions to the pure EVA, but generally higher CO yields than the base polymer under the most toxic fuel rich conditions. The exception to this was the sample containing ATH and zinc borate, which did not take up all the available oxygen under fuel rich conditions, and gave a much lower CO yield, corresponding to an eight-fold reduction in the combustion toxicity. Under fuel rich conditions for EVA, 60% of the carbon was lost as volatile organic species other than CO and CO2. For the sample containing zinc borate, this was 50% and for the remaining samples it varied from 20 to 38%. Evidence is presented which indicates that organic material trapped in the solid alumina residue is oxidised to CO, except in the presence of zinc borate, when it appears to be lost as organic carbon. (C) 2002 Elsevier Science Ltd. All rights reserved.