Curing of a thermosetting powder coating by means of DMTA, TMA and DSC

The curing of a thermosetting powder coating made up of carboxyl-terminated polyester and triglycidylisocyanurate (TGIC) was studied by means of dynamic mechanical thermal analysis (DMTA), thermal mechanical analysis (TMA) and differential scanning calorimetry (DSC). On the basis of isothermal curing of the coating on different supports with DMTA and TMA, we determine the degree of mechanical curing. The degree of chemical conversion is determined by curing the material isothermally and dynamically by DSC. In both cases, curing kinetics were established by means of isoconversional analysis and it was observed that both the technique and the support used appreciably modify the kinetics of the reaction process. Gelation was determined on the basis of the maximum for the loss tangent (tan δ) and in TMA as the point at which the shrinkage rate drops to zero and the dimensions of the material show no appreciable change. The relationship between the glass transition and the conversion (Tg–α) was established by means of DSC, DMTA and TMA. It is demonstrated that the degree of mechanical curing, determined on the basis of dynamic mechanical measurements, is an indicator of the progress of the reaction and up to gelation is always higher than the chemical curing level. The relationship between mechanical and chemical conversion serves as a point of connection between results obtained by means of TMA and DMTA and those obtained by means of DSC. Lastly, using the calorimetric kinetic data, the Tg–α relationship and conversion at gelation, we construct the TTT diagram for the curing of the coating.