| For decades, epoxy systems have shown outstanding physical properties for various applications with numerous advantages over other thermoset resins such as lower cure shrinkage, lower residual stress, chemical resistance, and insulating properties. However, property degradation due to hygrothermal exposure is a critical issue in applications, in which their nature to absorb moisture results in a significant loss in glass transition temperature (T g), modulus, tensile strength, and adhesive strength. These detrimental effects often include some complex behavior in that both increase and decrease in Tg and/or modulus is observed during the course of exposure.;In this study, to specifically describe the mechanism for this complex hygrothermal behavior, direct experimental measurement has been conducted employing thermodynamic analysis and spectroscopic measurements. Fourier transform near-infrared (FT-NIR) spectroscopic measurements showed that an increase in conversion was responsible for the increase in Tg, while plasticization occurred simultaneously, rendering the hygrothermal behavior to be complex. To evaluate those factors affecting this complex hygrothermal behavior separately, a relationship between Tg and conversion was constructed for the unexposed system and compared to the corresponding Tg values for the exposed system at the same point of each conversion value.;For another part of this dissertation, the effect of water on cure kinetics was investigated with the hypothesis that water significantly accelerates the cure kinetics of epoxy-amine systems. The near FT-IR demonstrated that a small amount of water addition significantly accelerated the cure reaction in terms of epoxide conversion. A modified mechanistic model was successfully used to directly compare the effect of hydroxyl from water addition and that from auto-acceleration by the reaction.;In the final section, in an effort to enhance the durability of bonding properties of an epoxy adhesive for structural strengthening application, silane coupling agents were applied to the surface of concrete before the adhesive was applied. Slant shear testing results show that the durability of the interfacial bonding was significantly enhanced with the use of an epoxy-functional silane coupling agent. The results indicate that the chemical nature of bonding plays a large role at the interface bonding of epoxy resin for structural strengthening applications. |
