A GENERALIZED METHODOLOGY TO DEVELOP PYROLYSIS MODELS FOR POLYMERIC MATERIALS CONTAINING REACTIVE FLAME RETARDANTS: RELATIONSHIP BETWEEN MATERIAL COMPOSITION AND FLAMMABILITY BEHAVIOR
Stoliarov, Stanislav I
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The development of effective flame retardant polymeric materials is of great interest to the fire protection community. To enable intelligent design of flame retardant polymeric materials, it is important to understand the relation between the material composition and the chemical and physical properties that control the fire growth process. This work details a generalized methodology to characterize flame retardant materials for the development of pyrolysis models that relate the fire behavior to material composition. The methodology employs thermogravimetric analysis, differential scanning calorimetry, and microscale combustion calorimetry, to measure the sample mass loss, heat required to decompose the sample, and the heat released from the complete combustion of the gaseous products evolved during the sample decomposition, respectively. Through inverse analysis of the milligram-scale experimental measurements using a numerical pyrolysis framework, ThermaKin2Ds, the decomposition kinetics and thermodynamics, and heats of combustion of gaseous pyrolyzate are determined. The chemical interactions between the polymer matrix and flame retardants are characterized by second-order (two-component) reactions. The resulting reaction model reproduces all aforementioned experiments with a high degree of detail as a function of heating rate and captures changes in the decomposition behavior with changes in the flame retardant contents. The methodology also utilizes a new bench-scale controlled atmosphere gasification apparatus to measure mass loss rate (MLR), back surface temperature, and sample shape profile evolution of 7-cm-diameter disk-shaped samples exposed to well-defined radiant heating. Inverse analysis of the bench-scale gasification experimental measurements using ThermaKin2Ds and the developed reaction model yields properties that define heat and mass transport in the pyrolyzing samples. This approach is demonstrated using two sets of materials: glass-fiber-reinforced polyamide 66 blended with red phosphorus and glass-fiber-reinforced polybutylene terephthalate blended with aluminum diethyl phosphinate and melamine polyphosphate. The resulting pyrolysis model is capable of predicting MLR data as a function of material composition and external heating condition. Idealized cone calorimetry simulations are conducted to demonstrate that, when the gas-phase combustion inhibition effect is excluded, aluminum diethyl phosphinate has a relatively minor impact on heat release rate, while the impacts of melamine polyphosphate and red phosphorus are significant.