Viscoelastic and Mechanical Properties of Epoxy/Mixed Amine Systems. Influence of Stoichiometry and Cure Conditions

Abstract

Epoxy networks based on the diglycidyl ether of bisphenol A (DGEBA) and a mixture of an aliphatic triamine and a difunctional cycloaliphatic diamine were studied. The glass transition temperatures of mixtures with different stoichiometric ratios were analysed by differential scanning calorimetry and dynamic mechanical techniques. The influence of the cure schedule was also studied for all mixtures, post-cured and not fully cured. Differences in crosslink densities were studied in the glass transition region. By using the average molecular weight between crosslinks, calculated using the rubber elasticity theory, the correlation between the glass transition temperature of cured systems and that corresponding to the unreacted system was determined. The variation of the glass transition temperatures was interpreted in terms of the macromolecular chain motions. Flexural properties such as modulus, strength, and strain to break were measured for the post-cured mixtures with different stoichiometrics.