Cure characterization of an unsaturated polyester resin using near-infrared, fluorescence and UV/visible reflection spectroscopies

This dissertation seeks to characterize the cure reaction of an unsaturated polyester resin using near-infrared, fluorescence and UV/Visible reflection spectroscopies. The results will provide a foundation for developing fiber-optic in-situ cure monitoring techniques based on near-infrared, fluorescence, and UV/Visible reflection spectroscopies for an unsaturated polyester resin system.^ Near-infrared spectra of the unsaturated polyester resin during cure showed a decrease in absorption at 1629, 2087, 2117, and 2227 nm. Model compounds representing the reactants and products of the cure reaction were characterized, and assignment of peaks in the NIR were made. Conversion of styrene and vinylene, determined from NIR measurements, were compared with values obtained using conventional FTIR measurements. Discrepancies between conversion values determined from NIR and FTIR measurements were attributed to a difference in sample sizes used for measurement. Using a microgel based reaction mechanism, the effects of temperature on the conversion of styrene and vinylene was discussed. ^ A strong fluorescence emission was found during cure of the unsaturated polyester resin. As the reaction proceeded, the emission intensity at 306 nm increased. Model compound studies confirmed that the unsaturated polyester vinylene component exhibits negligible fluorescence when excited at 250 nm. The fluorescence emission at 306 nm was attributed to a reduced self-quenching effect of styrene monomer. In-situ fluorescence characterization of the cure reaction was also attempted. Fiber-optic fluorescence measurements taken in-situ at 75°C were found to be higher than those taken by fiber-optics at room temperature, indicating a temperature effect on the fluorescence emission. These results may be a consequence of the static quenching behavior of styrene monomer. ^ UV/Visible reflection spectra of styrene showed a decrease in the % Reflectance at 255 nm with reaction time. This decrease was attributed to an overall reduction in the absorption index as styrene reacts to form polystyrene. Conversion of styrene calculated from UV/Visible reflection and FTIR measurements were in close agreement. A preliminary investigation into the use of UV/Visible reflection spectroscopy to cure monitor a styrene containing unsaturated polyester resin was also performed. A similar decrease in the % Reflectance at 255 nm with cure time was reported for the unsaturated polyester resin.