# Polyisocyanurate Foam Pyrolysis and Flame Spread Modeling
###### Abstract
The flammability of rigid polyurethane and PIR foams at various isocyanate index levels and filled with different flame retardants and blowing agents has been studied using a range of bench-scale methods [10; 11; 12; 13; 14]. [PERSON] et al. [10] studied flammability of polyurethane and PIR rigid foams of various densities using the limiting oxygen index and cone calorimetry. They found that the PIR foams had a superior fire response with respect to polyurethane foams and that an increase in density of either foam type increased the duration of burning but did not affect the peak heat release rate (HRR) measured in a cone calorimeter. They also analyzed scanning electron microscope (SEM) micrographs at different intervals of burning and found that the morphological structure of PIR foam was retained after complete flaming combustion, while a complete loss of closed-cell structure was observed for polyurethane foams. [PERSON] et al. [8] suggested that such morphological changes may impacts the contribution of convection and radiation to effective thermal conductivity, which should be taken into account for accurate modeling of heat and mass transport through the foam. [PERSON] and [PERSON] [11] investigated the flame retardancy effect of halogen-free, char-enhancing flame retardant compounds filled in varying quantities in pentane-blown PIR foams and found a significant reduction in peak HRR measured in cone calorimeter for compounds that induce a compact char layer development. In none of the aforementioned studies, a complete property set, commonly referred to as a pyrolysis model, was obtained for any rigid foam material. Thus, the purpose of the current work was to advance the state-of-the-art by developing such a property set. The methodology for pyrolysis model parameterization utilized in this work was developed in a series of studies and was successfully applied to non-charring and charring solid polymers with and without flame retardants [15; 16; 17; 18; 19; 20; 21; 22] and layered and fiber-reinforced structural composites [23; 24; 25; 26]. It has never been applied to polymeric foams. This methodology is based on a series of milligram-scale experiments, including TGA, DSC and Microscale Combustion Calorimetry (MCC), and gram-scale, radiation-driven gasification tests performed using the Controlled Atmosphere Pyrolysis Apparatus II (CAPA II) [27]. The mg-scale tests are analyzed to determine the decomposition reaction mechanism, kinetic parameters, and thermodynamics of the thermal decomposition of the condensed phase and the combustion of the gaseous pyrolyzate. The analysis of gram-scale test results is based on the thermal decomposition mechanism derived from the mg-scale experiments and is used to determine heat and mass transport parameters for the pyrolyzing material. The data obtained in the gram-scale tests are also used for the overall model validation. Both milligram- and gram-scale experiments are analyzed through inverse modeling with a numerical pyrolysis model, ThermaKin [20; 28; 29], which was recently supplemented with a set of automatic optimization tools [30], which make the analysis process significantly less time-consuming. In this work, this methodology was extended to include performance and modeling of the cone calorimetry experiments, which helped determine the contribution of the blowing agent present in the foam to foam's flammability. In addition, the foam was tested in a full-scale experiment, similar to the Single Burning Item (SBI) test [31], which is used to classify wall-lining materials, including insulation. Finally, modeling of flame spread in this experiment was carried out using the pyrolysis model developed in this work coupled with a recently developed empirical heat feedback model [32], which was formulated for this specific scenario using measurements performed on poly(methyl methacrylate) (PMMA).