Doctor of Philosophy in Chemistry
First Committee Member
David W. Hatchett, Chair
Second Committee Member
Third Committee Member
Graduate Faculty Representative
Number of Pages
Thermally processed PU foams are examined as a function of processing temperatures (25, 45, 65, and 85°C) at the side, middle, and center of a simple cylindrical mold. The PU foams show both chemical and morphological differences as a function of the processing temperature and radial position within the mold. Thermal degradation of uretoneimine structures, the emergence of carbodiimide structures, and extent of reaction of isocyanate groups are measured using photoacoustic FTIR spectroscopy. Chemical gradients and morphology differences between the side, middle, and center of the molded foam are observed for all processing temperatures. The data indicate that thermal activation at the center of the mold is important for samples regardless of processing temperature. Furthermore, in spite of thermal processing at temperatures well above the decomposition of uretoneimine structures (40°C), chemical gradients remain within the simple molded foams.
Thermally treated epoxy foams were found to undergo both chemical and structural changes associated with the degradation of Diels-Alder bonds and changing structural packing of siloxane units in the foam network. FTIR results show that these changes are not reversible and occur immediately after thermal exposure. The combination of changing chemistry, structure, and thermal expansion lower the overall density of the foam by approximately 41% relative to the pristine foam. The change in density also influences the modulus of the material which is reduced by 68% after ten thermal cycles. The results indicate that thermal exposure reduces the rigidity of the material through chemical and structural changes that cause the foam to expand, lowering the density and modulus in the process.
A composite material was successfully prepared by incorporating carbon black in PI. Platinum metal was successfully deposited on the resulting PI/Carbon film using cyclic voltammetry. Results obtained from four-point probe conductivity measurements show that increased carbon loading or platinum loading enhances the electrical conductivity of the composite. However, beyond 10% carbon loading, the mechanical integrity of the film is compromised. TGA and DSC results show that the thermal stability of PI is maintained with carbon incorporation and platinum deposition. PI/carbon/Pt was found be thermally stable up to 561°C as determined by DSC and 559°C as determined by TGA. SEM imaging suggests that carbon is well dispersed in PI while XPS results show that the platinum deposited Carbon/PI is metallic. The deposition of gold on carbon/PI was found to enhance its sensitivity to the ferricyanide redox couple. However, slower electron transfer is observed at both PI/Carbon/Pt and PI/Carbon/Au films as compared to Pt and Au planar electrodes.
Carbodiimides; Chemistry; Analytic; Diels-Alder reaction; Plastic foams; Polyurethanes
Analytical Chemistry | Materials Chemistry | Polymer Chemistry
University of Nevada, Las Vegas
Kinyanjui, John Macharia, "The synthesis and systematic evaluation of modified polymeric foams and electrically conductive polyimide/carbon/metal films" (2009). UNLV Theses, Dissertations, Professional Papers, and Capstones. 1136.
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