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Optimization of the curing process of epoxy resins using methods of structural analysis

Epoxy resins belong among materials frequently used for the production of impregnating composites especially for the construction of motors, generators, and transformers. During production, great emphasis must be focused on the proper curing process of these materials. Otherwise, it is not possible to guarantee the satisfactory properties of the final product. The paper is therefore focused on the analysis of the level of curing of epoxy resin by methods of structural analyses. The Fourier Transform Infrared Spectroscopy (FT-IR) and glass transition temperature evaluated from a reversible signal of heat flow measured by modulated differential scanning calorimetry (MDSC) were used. Curing process was performed in a laboratory oven. Partly and fully cured samples were analyzed during two independent experiments. These two experiments differ to each other especially by different times of sampling. The trend of the changes of infrared spectra measured on samples during the curing process corresponds well with the results of the glass transitions temperature measurements obtained by MDSC. Insufficient curing state is relatively well detectable by the presence of the spectral bands corresponding to the vibration of epoxy and anhydride groups (901, 1875, 1786 cm-1). Both methods are acceptable to detection of the curing level but with different sensitivity. While infrared spectroscopy is possible to use for prediction especially short times of curing, analysis of the glass transition is sensitive during the whole curing process.