Study of Physical States of Free Films of Pigmented and Clear Epoxy-Amine Coating Annealed at High Temperatures

Abstract

Epoxy-amine coatings cured at ambient conditions are known to contain residual solvent and unreacted monomers. These residuals have a direct effect on the physical state of the coating’s glass transition temperature, free volume, permeability, and water absorption properties. Free films of a pigmented and clear epoxy-amine coating were cured at ambient for seven days and annealed at 70 °C, 120 °C, and 150 °C for four hours under vacuum. Annealing at higher temperatures resulted in lower residual solvent content and a higher degree of cure. It was noted that the Tg increased by ~ 40% for the pigmented epoxy-amine and by ~ 130% for the clear epoxy-amine coating upon annealing at 150 °C for four hours under vacuum. Crosslink density, molar density, thermal expansion coefficient, and oxygen permeability were also measured for all the coatings. Molecular free volume was determined by measuring the fluorescence emission response of a molecular rotor probe incorporated into the coatings. The results also demonstrated the effect of pigmentation on the physical states of the coating at higher annealing temperatures.