Modelling polymeric material using Microscale combustion calorimetry and other small scale data

A challenge encountered by many practicing fire engineer carrying out fire modelling is that the combustible fuel is not completely well-known. Practical materials may, for instance, be identified as some well-known polymer, but this is usually not the whole truth from the viewpoint of the fire behaviour. Besides of the nominal polymer, the blend may include large quantities of different additives that affect the thermal degradation and combustion of the material. Until now, the effect of these additives has been taken into account in the modelling by adjusting the thermal parameters when fitting the model to the cone calorimeter results. Such a model captures the joint effect of all the components, but cannot distinguish between the combustible volatiles from additives and main polymer, which may lead to inaccurate prediction if the conditions, such as the heating rate, are significantly different. In this work we use Microscale Combustion Calorimetry for building a more accurate model of the polymer pyrolysis by combining the heat release rate measurements with the mass loss rate measured in Thermogravimetric Analysis. Two methods are developed and tested using a generic sample and a real PVC sheath of an electric cable. The results show that the methods are able to calculate the heat release rate correctly for the tested materials, and also estimating the sample composition to some extent. Symbols A Pre-exponential factor (s) Greek cp Specific heat capacity (kJ/kg/K) α Conversion E Activation energy (kJ/mol) β Heating rate (K/s) ΔH Heat of reaction (kJ/kg) ε Emissivity ΔHc Heat of combustion (kJ/kg) ρ Density (kg/m) k Thermal conductivity (W/m/K) m Mass (kg) Subscripts m Mass loss rate (kg/s) 0 Initial nc Number of components eff Effective value nO2 Reaction order of oxidation F Fuel gas np Number of (gaseous) products. i Reaction index nr Number of reactions I Inert gas N Reaction order j Component index Qc Heat release (kJ) Z Residue c Q Heat release rate (kW) Q/m0 Total heat release in MCC (MJ/kg) Z Residue yield (of total mass) T Temperature (K)