Mechanical Engineering
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Item A COMPREHENSIVE CHARACTERIZATION OF PYROLYSIS AND COMBUSTION OF INTUMESCENT AND CHARRING POLYMERS USING TWO-DIMENSIONAL MODELING: A RELATIONSHIP BETWEEN THERMAL TRANSPORT AND THE PHYSICAL STRUCTURE OF THE INTUMESCENT CHAR(2019) Swann, Joshua; Stoliarov, Stanislav I; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A quantitative understanding of an intumescent material’s reaction to fire remains largely an unsolved challenge. More specifically, the relationship between thermal transport and the resulting char structure is not well understood. Improved pyrolysis models for intumescent materials are necessary to advance the fields of fire modeling and material development. To aid in this endeavor, a systematic methodology to parameterize comprehensive pyrolysis models for charring and intumescent materials is presented. Rigid poly(vinyl chloride), flexible poly(vinyl chloride), Bisphenol A poly(carbonate), poly(ether ether ketone), and poly(vinylidene fluoride) were analyzed in this work. First, thermogravimetric analysis and differential scanning calorimetry were employed simultaneously to characterize the kinetics and thermodynamics of thermal decomposition. Microscale combustion calorimetry was utilized to parameterize the heats of complete combustion of gaseous pyrolyzates. ThermaKin, a numerical pyrolysis solver, was employed to inversely analyze all milligram-scale tests. A multi-step reaction mechanism, consisting of sequential steps, was constructed to capture all observed physical changes and chemical reactions. Gasification tests were conducted on 0.07 m diameter disk-shaped samples using the newly developed Controlled Atmosphere Pyrolysis Apparatus II to parameterize the thermal transport within the undecomposed material and developing char layer. A recently expanded version of ThermaKin, ThermaKin2Ds, was employed to inversely model the gasification experimental results. The model accounted for spatially non-uniform swelling of the sample and the ensuing changes within the thermal boundary conditions. The resulting two-dimensional models were shown to reproduce the experimental sample shape profiles, unexposed surface temperatures, and mass loss rates with excellent accuracy. An analysis of the char pore structure was also conducted to determine the pore size distribution and char porosity. Further analysis enabled the mean, median, and volume-weighted mean pore diameters to be computed from pore size distributions. Quantitative relationships were subsequently developed between relevant thermal transport quantities and the char’s physical structure. It was determined that the thermal insulating potential of the fully developed char was related to the number of pore walls positioned perpendicular to the direction of heat flow. Therefore, designing charring polymers capable of producing many small pores will aid in the development of intumescent materials with an enhanced thermal insulating potential.Item A GENERALIZED METHODOLOGY TO DEVELOP PYROLYSIS MODELS FOR POLYMERIC MATERIALS CONTAINING REACTIVE FLAME RETARDANTS: RELATIONSHIP BETWEEN MATERIAL COMPOSITION AND FLAMMABILITY BEHAVIOR(2018) Ding, Yan; Stoliarov, Stanislav I; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)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.