A study of the thermal decomposition and smoke suppression of poly(vinyl chloride) treated with metal oxides using a cone calorimeter at a high incident heat flux

Abstract

An investigation of the thermal decomposition, the flame retardancy and the smoke emission behaviour of PVC formulations containing the transition metal oxides, Cu2O, CuO, MoO3 and Fe2O3, was carried out using a cone calorimeter at an incident heat flux of 50 kW m−2. The experimental data indicate that the four transition metal oxides show good flame retardancy and smoke suppression by effectively reducing peak and average heat release rate (pk-HRR and av-HRR), peak smoke production rate (pk-SPR) and total smoke production (TSP). Oxides of copper are more effective than MoO3 and Fe2O3 in reducing smoke emission in PVC. The values of pk-HRR, av-HRR, pk-SPR and TSP decrease with increasing addition of the transition metal oxides. The metal oxides obviously enhance average effective heat of combustion (av-EHC). This fact is well supported by the extensive literature regarding pyrolysis of PVC. At an addition level of 4 mol of metal atom in the oxides based upon 100 moles chlorine in PVC, Cu2O, CuO, MoO3 and Fe2O3 reduce smoke emission by 49.6, 52.0, 25.1 and 33.0%, respectively. Compared with the results obtained by NBS smoke chamber in the literature, the efficiency of some suppression of MoO3 and Fe2O3 obviously decreases in the cone calorimeter at an incident heat flux of 50 kW m−2. The transition metal oxides can change the thermal decomposition behavior of PVC. They significantly reduce mass loss rate (MLR) and mass loss (ML) of PVC backbone, and promote char residue formation at the end of flaming. Cu2O, CuO and Fe2O3 catalyzed HCl-elimination reaction of PVC, while MoO3 stabilized it according to data of the thermal decomposition of PVC. A comparison of HRR curves, SPR curves and MLR curves gives a better understanding of flame retardancy and smoke suppression at the high incident heat flux.