Modeling the thermal degradation of poly(methyl methacrylate)/carbon nanotube nanocomposites

The thermal degradation is modeled of a one-dimensional disk of poly(methyl methacrylate) (PMMA) with and without the dispersion of carbon nanotubes exposed to a fire-level heat flux. The description of the chief transport processes (conductive, convective and radiative heat transfer, convective mass transport) is combined with a one-step finite-rate reaction for polymer decomposition resulting in surface ablation (absence of nanotubes) or the formation of network-structured continuous layer of carbon nanotubes. Good agreement is obtained between the predicted and measured mass loss rates for the two cases. The presence of nanotubes reduces the peak in the mass loss rate and increases the conversion time, owing to the insulating effects of the surface layer and the much larger surface re-radiation losses. The effects of flame retardance are enhanced by increasing the growth rate and/or the thickness of the surface layer.