A critical mass flux model for the flammability of thermoplastics

Abstract

The combustion of thermoplastics is modelled using a critical mass flux hypothesis as the ignition and extinction criteria. Polymer degradation is modelled as a single-step first-order Arrhenius reaction term. A simple model for mass transport of polymer through the sample during pyrolysis is included. The degradation products are assumed to move out of the polymer instantaneously. The model consists of a nonlinear integral-differential advection-diffusion equation for the temperature in the thermoplastic, coupled to an ordinary differential equation, for the regression rate. Results are presented which quantify the effect that the thickness of the test sample has on the mass-loss rate, or equivalently heat-release rate, curve. From these we conclude that thermally thick samples are characterized by a region of steady burning which is independent of the initial sample thickness. The test method that we have in mind is the cone calorimeter.