Award Date

5-2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

First Committee Member

David W. Hatchett, Chair

Second Committee Member

Clemens Heske

Third Committee Member

Spencer Steinberg

Graduate Faculty Representative

Brendan O'Toole

Number of Pages

160

Abstract

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.

Keywords

Carbodiimides; Chemistry; Analytic; Diels-Alder reaction; Plastic foams; Polyurethanes

Disciplines

Analytical Chemistry | Materials Chemistry | Polymer Chemistry

File Format

pdf

Degree Grantor

University of Nevada, Las Vegas

Language

English

Comments

Signatures have been redacted for privacy and security measures.

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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