A numerical study of thermal degradation of polymers: Surface and in-depth absorption

A one-dimension numerical model is developed in this study to investigate numerically the absorption effect, including surface and in-depth absorption, on thermal degradation process that occurs in polymer gasification. Surface and in-depth absorption hypotheses, most commonly used in literatures and their effect on the simulation results are discussed. Three polymers are selected to conduct the simulation: Poly(methyl Methacrylate) (clear PMMA), High Impact Polystyrene (HIPS) and Poly(acrylonitrile Butadiene Styrene) (ABS). The availability of the developed model is verified by the published experimental data. The result indicates that large temperature gradient exists in the heat penetration layer for surface absorption, and in-depth absorption leads to a relatively uniform temperature distribution in this layer. Top surface temperature increases with increasing heat flux (HF) and higher value is observed for surface absorption than that of in-depth absorption. The model overestimates the mass loss rate of ABS at low HF due to the negligence of existence of a thin char layer generated on the surface of sample which cracks immediately after generation under high HF. Good agreement between the numerical and experimental results of polymers suggests that both assumptions are acceptable in modeling bench scale tests.