LAUSR

This study presents dynamic modeling of the thermal degradation of polyethylene (PE) in an oxidizing atmosphere. The purpose of the work is to calculate the degradation rate of samples placed in a macro-thermobalance. The model is composed of two coupled sub-models: the first one describes the processes occurring in the condensed phase (where termal degradation of PE in lighter molecule occurs) while the second one accounts for the processes occurring in the gaseous phase. The condensed phase model allows for the evaluation of the rate at which combustible gas is produced by PE pyrolysis and the gas phase model computes the gaseous oxidation of the products of pyrolyse and subsequent heat flux transferred back to the sample. This second model relies on the use CFD (Ansys Fluent) where turbulent combustion of octane (which is supposed to be the product of PE Pyrolysis) is accounted for thanks to eddy dissipation approximation. The effect of the filling height in the sample crucible containing the polyethylene is studied. The experimental results from macro TGA (MTGA) and from the mathematical model are compared. Three different behaviors associated to crucible filling height are highlighted. For small ones, kinetics of pyrolysis is the overall limiting phenomenon, whereas heat transfer to the sample is the limiting one for high filling heights. Both experimental and numerical findings show that the position of the flame in the vincity of the crucible (inside or outside and surrounding it) is the key parameter in polyethylene’s degradation rate.