A methodology for characterizing reactive coatings: Time–temperature–transformation (TTT) analysis of the competition between cure,evaporation, and thermal degradation for an epoxy-phenolic system

A methodology, in terms of a macroscopic isothermal time–temperature–transformation (TTT) diagram, is presented for characterizing the changes that occur isothermally in a reactive thermosetting system in which evaporation, cure, and thermal degradation occur. Iso-weight loss contours show the progress of the loss of volatile material (mostly solvent). The gelation contour corresponds to the macroscopic viscosity rising to a definite level. The vitrification contour corresponds to the glass transition temperature (T_g) rising to the temperature of cure (T_cure). Iso-T_g contours show the progress of cure in terms of the easily measured T_g (rather than chemical conversion). The iso-T_g contours also show the influence of thermal degradation competing with cure. Degradation is responsible for difficulties in assigning the glass transition temperature of the fully cured material (i.e., T_g∞).