Characterization of pyrolysis and combustion of rigid poly(vinyl chloride) using two-dimensional modeling

Abstract

A quantitative understanding of an intumescent material’s reaction to fire is largely an unsolved challenge in the field of fire science. To advance fire modeling, a systematic methodology to fully parameterize a comprehensive pyrolysis model for charring and intumescent materials is presented. Thermogravimetric analysis, differential scanning calorimetry and microscale combustion calorimetry were employed to characterize the kinetics and thermodynamics of thermal decomposition and heats of complete combustion of gaseous pyrolyzates. A multi-step reaction mechanism, consisting of sequential steps, was constructed to capture the physical transformations and chemical reactions observed in all milligram-scale experiments. Controlled Atmosphere Pyrolysis Apparatus II gasification experiments were conducted on 0.07 m diameter disk-shaped samples to parameterize the thermal transport within the undecomposed material and developing char layer. A recently expanded fully verified and validated numerical framework, ThermaKin2Ds, was employed to inversely model the gasification experimental results. The model accounted for spatially non-uniform swelling of the sample and associated changes in the radiant heat exposure. Rigid poly(vinyl chloride), a widely used intumescent material, was analyzed in this work. The resulting two-dimensional model was shown to reproduce the gasification experimental unexposed surface temperatures and mass loss rates with a mean error of 3.9% and 12.6%, respectively. A preliminary analysis of the char pore structure was also conducted to determine the pore size distribution and char porosity. The resulting porosity based on the density of graphite and the porosity based on image analysis (including only the pores that are greater than 1 × 10−4 m in diameter) was found to be 0.96 and 0.53, respectively.