Online near-infrared measurements of an epoxy cure process compared to mathematical modeling based on differential scanning calorimetry measurements

• Published in: Journal of applied polymer science 2008-11, Vol.110 (4), p.2184-2194
• Main Authors: Friis-Pedersen, H.-H, Houmøller, L.P, Storm, B.K
• Format: Article
• Language: English
• Subjects: Applied sciences; curing of polymers; differential scanning calorimetry (DSC); Exact sciences and technology; Forms of application and semi-finished materials; infrared spectroscopy; kinetics (polym.); Laminates; Polymer industry, paints, wood; Technology of polymers; thermosets
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.28407

An epoxy resin containing diglycidyl ether of bisphenol A, dicyandiamide, and an accelerator (diurone) was investigated under different cure cycles. The mathematical prediction of the degree of cure in a thermoset as a function of time and temperature was investigated and compared to measured data. Near-infrared analysis was used to measure the conversion of epoxy and primary amine and the production of hydroxyl. Modulated differential scanning calorimetry was used to measure the changes in the heat capacity during cure. The measurements revealed differences in the primary amine conversion and hydroxyl production, and close relations to the measurements of heat capacity were found. The measurements of the degree of cure revealed that cure cycles initiated at 80°C produced a lower degree of cure than cure cycles initiated at 90°C, although all cure cycles were postcured at 110°C. These findings were to some degree supported by measurements of the primary amine conversion and hydroxyl production. The characteristics found were attributed to differences in the cure mechanisms. The mathematical model did not incorporate these differences, and this may have led to discrepancies between the predicted and actual values of the degree of cure.