Estimation of heat release rate for polymer–filler composites by cone calorimetry

Effects of endothermic behaviour of typical flame retardant fillers on the heat release rate measurement using the cone calorimeter have been studied. It was found that without appropriate corrections, the heat release rate measured by the cone calorimeter for the polymer composites containing large quantities of endothermic fillers would be overestimated. Some typical materials have been studied quantitatively, including alumina trihydrate and magnesium hydroxide added in three different polymers. The theoretical calculations show that for alumina trihydrate at 70 wt% loading level, the total heat released from the polypropylene based composite would be 6.5% less than that for the composite without the corrections, 11.2% less for the PMMA based composite and 17.0% less for the plasticised polyvinyl chloride (PVC) based composite. For magnesium hydroxide at the filler loading level of 70 wt%, the total heat released for the polypropylene based composite would be 7.7% less, for the PMMA based composite 13.4% less and for the plasticised PVC based composite 20.3% less. A procedure for correcting the heat release rate measured by the cone calorimeter is put forward in the paper, which uses the decomposition heat of the fillers to modify the effective heat of combustion measured for the composites and then multiply the modified effective heat of combustion by the mass loss rates measured for the composites to re-calculate the heat release rates, giving a more accurate measurement. Also, the heat release rates corrected by the proposed method and the heat release rates initially measured by the cone calorimeter for the polypropylene–alumina trihydrate composite were compared, demonstrating the necessity and significance of the corrections.