Different combustion modes and flame shapes in massive loads of polyethylene revealed by macro-thermogravimetry

While thermogravimetric analysis can reveal the reaction mechanisms that occur during combustions, it cannot be used to study reactions involving large fuel loads. A large capacity thermobalance reactor is thus required to reveal thermal events that can have a substantial effect on reaction rates. The study presented in this article highlights the value of using macro-thermogravimetry to study the combustion of large loads of polyethylene, a representative thermoplastic polymer. A coupled analysis of mass loss and the corresponding heat flows reveals three distinct combustion regimes, which differ by the shape and position of the flame, which either remains above or, transiently or continuously, wraps around the load. In the first case, radiation from the flame only affects the upper surface of the load and has little effect on the combustion rate. In the second case, the integrated effect of this radiation on part of the outer surface of the crucible substantially accelerates the process, which eventually slows as the flame relocates above the charge. The third regime occurs for large loads, when the filling factor of the reactor is high. The radiation affects the entire external surface of the load, leading to very high combustion rates until the polymer is completely consumed. Simulations of the combustion process support the conclusions derived from experimental data. These results should prove valuable for the development of robust and effective techniques to destroy dangerous organic materials. (authors)