Structure property correlation of epoxy resins under the influence of moisture and temperature; and comparison of diffusion coefficient with MD-simulations

We made a structure property correlation (SPC) by altering systematically the chemistry of a cross-linked epoxy resin and examining the material behaviour and failure mechanisms under the external influence of moisture, temperature and stress. The epoxy resin (aromatic epoxy: 1,3-Bis-(2,3-epoxypropyl)-benzene and amine hardener: 1,2-Diaminoethan ) was examined under different loading conditions (65degC/75rh, 85degC/85rh & 98degC/100rh). The stoichiometry (2/1 and 4/3) was changed and in parallel the molecular weight of the hardener was increased (2, 4 and 6 carbons), thus ending with 6 materials. Under these conditions we made gravimetric measurements to obtain the diffusion coefficient (D) and the maximum water concentration (Csat), which was input data for the Molecular Dynamic (MD) simulations. As representative structure for the simulation we introduce the so called pseudo-cut model: partly reacted hardeners and epoxy resins representing the polarity of the system as if it was fully reacted. The result showed the dependency of the diffusion coefficient on the crosslinks. For thermomechanical characterization we performed (Storage Modulus E', Glass Transition Temperature Tg and Coefficient of Thermal Expansion-alpha). The expected tendency was followed in all the experiments, which showed dependency on structure and water concentration.