TGA Maximum Heat Release Rate and Mass Loss Rate and Comparison with the Cone Calorimeter

Thermogravimetric analysis (TGA) is a fundamental tool to study the degradation and pyrolysis behaviours of milligram-sized samples in inert or oxidising atmospheres. One of the most important outputs of TGA measurements is the maximum heat release rate (MHRR) or the maximum mass loss rate (MMLR). Analytical solutions of the MHHR/MMLR have been developed for infinitely fast heat transfer between the gas and solid. It has also been proposed that the MHRR in a TGA apparatus is proportional to the heat of combustion divided by the heat of gasification of the material. This conclusion was reached by the observed nearly linear relation of the MHRR in the TGA with the heat release rate per unit area in the cone calorimeter for thermally thick samples. In this work, we investigate the MMLR in the TGA for both finite and infinite rates heat transfer by analytical solutions and numerical calculations. A universal expression between the MMLR and equipment and material parameters is deduced. The derived expression is subsequently validated against experimental data of two polymers (PA6 and PBT). Finally, we discuss how the pyrolysis rate or heat release rate for a thermally thick solid, as measured for example in a cone calorimeter, is related with the MMLR in the TGA apparatus.