In situ monitoring of epoxy resin curing process: Using glass transition as a bridge

Dielectric analysis (DEA) is an effective method for monitoring the curing process of epoxy resin (EP) in situ, but the influence of curing temperature on the measurement results limits the application of DEA in curing process monitoring with variable temperature. In this study, the theoretical basis of using the glass transition as a bridge and monitoring the curing degree by ionic conductivity was analyzed. DEA experiments and differential scanning calorimeter (DSC) experiments were carried out and the mathematical model of ionic conductivity, glass transition temperature, and curing degree of the EP established. The parameters in the model were only related to the composition of EP system in the model as verified for implementing curing-degree monitoring of the EP system cured at variable temperature. The FT-IR spectra measurement was carried out and the activation energy of curing reaction was calculated by results of DEA and DSC, which verified the reliability and scientificity of the method. The method of using glass transition as a bridge can monitor the curing degree in the curing process with variable temperature and extends DEA to the monitoring of this process under variable temperatures.