Mechanical Properties of Heavy Duty Epoxy Coatings

Abstract

In a first stage, the composition of epoxy coatings is discussed with special focus on the mechanism of curing and the chemistry of curing agents and their advantages and downturns in prospect to their use in the manufacture of epoxy resins. Then literature on the causes of increased brittleness, cracking and degradation of epoxy resins was studied, especially in relation to evolution of the resins in the glassy state, hydrothermal aging and also in relation to chemical aging. The first part of the experimental work is focused in the obtention of optimal paint films and the observation of the effects that different substrates have in the formation of defects and the ease of release. It was found that the silicone substrate had the best performance in terms of adhesion, but PE plates and plastic folders yielded more regular films. In a second stage, the rheological properties of paint films were studied through small amplitude oscillatory strain techniques. Thermal behaviour and transitions were studied through DSC analysis. Those procedures were also applied to evaluate the effects of water sorption on the resins. Results indicated that despite the differences, rheological behaviour in the glassy state was very similar for both resins when they were unexposed. On the other hand, when they had undergone moisture uptake, values of shear loss and storage modulus changed differently, depending on the type of resin. Moisture uptake was studied through TGA and gravimetry, but the results were unclear. Experiments involving a temperature ramp showed differences in the speed of cure of the resins. It was found that, with the same curing programme, Resin A was almost fully cured after a week and Resin B was not. This seemed to have an effect on stress formation. Finally, standard methods were conducted onto the chosen epoxy resins, applied in steel surface. This allowed evaluating flexibility and internal stress developed in the curing process of the paint. Findings suggest that the methods are capable of giving complementary information. In particular, the standard methods chosen were able to provide information that was slightly more clear when the resins were in the glassy state.