Detection and modelling of thermal and rheological transitions of a 2-step-curing thermoset using dielectric and standard measuring techniques

Process monitoring is gaining increased attention in the field of fiber reinforced plastic manufacturing. One of the vital aspects hereby is the control of the curing degree of the components, in order to ensure the quality of the composite. In this work dielectric analysis (DEA) as an online-capable monitoring system is investigated in comparison to standard thermo-physical and rheological measurement techniques. Therefore, a pultrusion-grade two-step curing hybrid thermoset matrix was analyzed using DEA as well as rheometry and differential scanning calorimetry (DSC). The measurements were performed under dynamic temperature profiles (constant heating rates of 0.5, 1 and 5 K/min) in the range of -20 to 185 °C. A good qualitative correlation was found for both reaction steps between the shear viscosity measured by oscillated parallel plate and electric-based ion viscosity detected by DEA. The observed reaction steps were confirmed with DSC measurements. By fitting measured data of different heating rates, kinetic models for DEA, DSC and rheology were developed, allowing the prediction of the curing degree under varying process conditions. The models were finally validated through various temperature profiles, proving good agreement between measured and predicted data.