Determination of pyrolysis and combustion properties of poly(vinylidene fluoride) using comprehensive modeling: Relating heat transfer to the intumescent char's porous structure

Abstract A systematic methodology, utilizing improved experimental and numerical techniques, is used to analyze the heat transfer within an intumescent char. Thermogravimetric analysis, differential scanning calorimetry and microscale combustion calorimetry were conducted on 4–7 mg samples to determine the kinetics and thermodynamics of thermal decomposition and heats of complete combustion of gaseous pyrolyzates. Subsequently, 0.07 m diameter disk-shaped samples were pyrolyzed in the Controlled Atmosphere Pyrolysis Apparatus II to characterize the thermal transport within the decomposing solid and evolving char layer. ThermaKin2Ds was employed to analyze all the experimental data, using inverse analysis techniques, and to perform predictions. Poly(vinylidene fluoride), a widely used intumescent polymer, was investigated in this study. The model parameterization process revealed notable instabilities in the sample surface emissivity during pyrolysis. However, the resulting model can predict the experimental gasification mass loss rate with a mean error of 29%. Additionally, the physical structure of the porous char was analyzed to enable the formulation of quantitative relationships between relevant thermal transport parameters and the intumescent char's structure. A prominent linear correlation was revealed during this exercise: the product of density and thermal conductivity was directly proportional to an increasing char porosity derived from image analysis.