Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item IMPROVEMENTS TO REFRIGERANT FLAMMABILITY TESTING THROUGH USE OF A POLYCARBONATE APPARATUS(2017) Reymann, Jonathan; Sunderland, Peter B; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There is a new generation of mildly flammable refrigerants that pose unique challenges to flammability limit testing with ASTM E681. This test standard relies on visual observation of flame propagation inside of a spherical glass vessel. The combustion of these refrigerants etches the glass test vessel, making it difficult to properly observe the flame. The current standard specifies the electrodes to be placed vertically in the flame path, hindering the propagation of the flame. The rubber stopper that seals the vessel is prone to leak and also vent before the flame fully propagates, skewing the results of the test. These problems have been addressed through the creation of a polycarbonate testing apparatus that utilizes a weighted rubber stopper and electrodes that penetrate through the side of the vessel. This prototype was tested extensively with R-32, and yield a lower flammability limit of 14.8% when testing with a starting pressure of 91.2 kPa. The polycarbonate prototype proved to be an adequate alternative to the glass flask, and provided solutions to the etching, quenching, and venting issues.Item SYNTHESIS AND CHARACTERIZATION OF LOW FLAMMABILITY POLYMER/LAYERED SILICATE NANOCOMPOSITES(2009) Zhang, Xin; Briber, Robert M.; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There has been significant interest in the applications of polymer nanocomposites in a variety of areas. Polymer/layered silicate nanocomposites have been of interest because of relatively low raw material cost and improved materials properties such as higher Young's modulus, higher thermal deformation temperature, lower small molecule permeability, lower density (compared to metals and traditional glass fiber reinforced composites) as well as low flammability. The relationships between the flammability and the dispersion of the layered silicate platelets inside the polymer matrix is just being established. The complete set of factors that affect the flammability of polymer/layered nanocomposites are not fully identified. In this thesis polymer/layered silicate nanocomposites with different degrees of platelet dispersion were synthesized. The structure of the nanocomposites was characterized by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). The flammability of these nanocomposites was characterized by TGA, cone calorimetry and gasification. By coupling the structural and flammability data it has been concluded that forming a nanometer scale dispersed structure significantly improves the flammability but the details of the degree of dispersion are not critical. The improvement in the flammability arises from the formation of a residue or char layer at the surface of the nanocomposite. This residue layer acts as a radiation shield and as a physical barrier preventing the polymer degradation products from escaping and acting as fuel. It is observed that the stability of the residue layer formed during combustion has major impact on the flammability. This thesis also describes work to improve the flammability of the polymer/layered silicate nanocomposites by enhancing char/residue formation in order to improve the residue layer stability.Item FLAMMABILITY CHARACTERISTICS OF WATER-BASED POLYCRYLIC AND OIL-BASED POLYURETHANE COATED OAK VENEER PLYWOOD SAMPLES SUBJECTED TO INCIDENT HEAT FLUXES(2005-12-13) Thompson, Sarah Elizabeth; Mowrer, Frederick W.; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The flammability characteristics of oak veneer plywood were evaluated in the Cone Calorimeter. Samples of 6.35 mm (1/4 in.) thick and 19.05 mm (3/4 in.) thick oak veneer plywood were coated with 3, 6, and 9 coats of either oil-based polyurethane or water-based polycrylic clear finishes and tested at incident heat fluxes of 35, 50, and 75 kW/m2 along with uncoated samples. Both the type of finish and the number of coatings were found to influence the ignition time, the measured peak heat release rate, and the minimum flux for ignition of the samples. The ignition times for the coated samples were 2 to 3 times lower than the unfinished samples. Predicted times to ignition differed by a factor of 2 to 3 from the measured values (with the exception of the samples with nine coats of finish.) The predicted ignition temperatures differed by as much as 100 ºC from the measured temperatures. The Quintiere flammability parameter, b, was found to be positive for all testing scenarios, suggesting a propensity for flame spread at the incident heat fluxes evaluated.