Accurate prediction of viscosity profile during curing is critical for epoxy resin processing, particularly for lamination operations where flow behavior and cure development are strongly coupled. In this work, an isoconversional state diagram (ISD)-based viscosity modeling framework formulated within a three-regime model (TRM) is proposed to reconstruct the complete complex viscosity profile of a B-staged epoxy prepreg under constant heating rate nonisothermal and arbitrary heating conditions. The approach combines an Eyring-type description of melt-viscosity with an ISD-based representation of the curing-dominated regime, in which the extent of conversion is defined directly from characteristic complex viscosity points obtained from rheological measurements. The proposed framework yields physically bounded viscosity profiles that naturally terminate at a finite plateau corresponding to the fully cured state, without reliance on calorimetric input. The corrective effect in the ISD method stabilizes state-curve construction and mitigates distortions caused by experimental scatter. Validation using a commercial epoxy resin system demonstrates good agreement between predicted and measured complex viscosity curves under both constant heating rates and realistic press temperature profiles. A comparison between differential scanning calorimetry-based and rheology-based ISD constructions further illustrates the influence of conversion definition on predicted curing behavior. Overall, the proposed TRM-ISD framework provides a robust and process-relevant tool for complex viscosity prediction in epoxy resin systems.
Tao et al. (Mon,) studied this question.