APPLICATIONS OF SIMULTANEOUS DSC FTIR ANALYSIS

A combination of the standard laboratory techniques differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy is described. This simultaneous DSC/FTIR technique gives spectroscopic and thermodynamic information about a solid or liquid sample undergoing thermal modification. DSC measures the exothermic and endothermic responses of the samples, while the FTIR analysis observes their changes in chemical and physical composition. Reflectance infrared microspectroscopy was employed to examine the samples. Two epoxy samples were studied by DSC/FTIR. Both samples were mixtures of diglycidyl ether of Bisphenol A with a cycloaliphatic primary amine. The two samples differed only in the amount of primary amine used to crosslink the epoxy resin. The cure of each specimen was studied by using the reflectance/absorbance mode of infrared analysis, while simultaneously undergoing a DSC experiment. Samples were monitored as a function of secondary amine content, crosslink density, and hydroxyl formation. This information was used to examine whether the samples differed in their overall reaction rates. The samples did in fact exhibit markedly different cure character, giving insight into the reaction routes and a prediction of the final molecular structures achieved by these small changes in the ratio of resin to amine activator. A sample of poly(ethylene terephthalate) (PET) was also analyzed by DSC/FTIR; in this case the specular reflectance mode of infrared analysis was employed. DSC was used to detect the glass transition, multiple melting endotherms and recrystallization of the polymer as it was heated and cooled. FTIR was used to monitor structural changes in the sample as it went through these thermal transitions. These experiments demonstrate the high potential of DSC/FTIR reflectance microspectroscopy when studying the thermal characteristics of materials.