UV reflection and luminescence for characterization of cure in epoxies, polyimides and composites

Date of Completion

January 1994


Chemistry, Polymer|Physics, Optics




In order to develop new optical methods, a UV reflection technique was investigated to characterize cure in epoxies, polyimides and their composites. The UV reflection technique in an aromatic diamine-cured epoxy system resulted in the spectral shift of 22nm which was correlated with the extent of epoxide reaction. Based on this result, fiber optic reflection method was implemented for in-situ characterization of epoxy composites at cure temperatures. During imidization, spectra were blue shifted. Deconvolution of the reflection spectra based on the spectra of the starting polyamic acid and final polyimide provided quantitative extent of imidization.^ Charge transfer (CT) fluorescence of several aromatic group containing polyimides was studied by changing diamine and dianhydride components. The fluorescence spectra showed red shifts and their intensities decreased as the imidization proceeded. UV absorption showed the identical amount of spectral shift as CT fluorescence excitation spectra. Finally, these spectral changes were correlated with the extent of imidization for several aromatic polyimide systems.^ The fluorescence technique was used for the study of interphase of epoxy/glass or carbon composites. For the interphase region, the cure reaction was faster at the early stage of cure even though the final cure state was similar as that of the bulk system. The effect of surface treatment was studied by a model system and an actual interphase. Amino-silane treatment on a glass interphase showed about 17% increase in crosslinking density, while water aging and air oxidation showed almost no effect. Air oxidation showed a faster reaction at the early stage of cure for the case of a simulated carbon interphase. In the case of epoxy/carbon composite, both air oxidation and water aging treatment showed a faster cure reaction at the early stage of cure. The air oxidation treatment for the epoxy/carbon composite showed a 10% improvement of the crosslinking density. ^