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Abstract  

The curing of a thermoreactive alkyd-melamine-formaldehyde resin system was investigated by rheologycal, TG and TMA-analysis, in order to construct the time-temperature-transformation diagram. The points of the gelation curve were determined by measuring the increase in viscosity during isothermal curing at different temperatures. A power-function could be fitted to the gelation curve, which is suitable to estimate gelation at any curing conditions, as well as to establish storage conditions. The reaction in the resin matrix was followed by monitoring the loss of mass during isothermal curing at different temperatures. The final section of the resulted iso-curing temperature (iso-T cure) diagrams could be fitted with logarithmic functions, which may be used for estimating the conditions needed to a given, desirable mass loss, i.e. conversion. The steepness of the curves increases with temperature suggesting the forthcoming of degradation during cure with increasing temperature. From these data the iso-mass loss curves of the TTT-diagram were constructed. For determining the iso-Tg curves of the TTT-diagram isothermal curing was carried out in a drying oven at different temperatures, followed by TMA measurements. The iso-Tcure diagrams served to determine T g , and to construct the iso-T g curves of the TTT diagram. Vitrification curve is far beyond conditions of storage, curing and degradation, meaning that the resin matrix is in rubbery physical state before, during and after the cure. Curing conditions resulting degradation can also be estimated from the TTT-diagram.

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Abstract  

The gelation of a powder coating and its matrix based on a saturated carboxyl functional polyester resin and triglycidyl isocyanurate of different diastereomer racemate composition was investigated by rotational viscometry. The iso-T cure diagrams have been determined directly by isothermal viscometric measurements and the gelation curves for the TTT-diagram have been constructed. To the measured section of the gelation curves power functions could be fitted and with their help the reactivity of the investigated systems were compared. The ratio of the two diastereomer racemates of TGIC has a significant effect on the reactivity of the coating, as it was also supported by DSC measurements. β-TGIC is of highest reactivity, and by increasing its ratio in TGIC, reactivity increases, and adversely effects the performance of the powder coating. Commercial TGIC-s have similar reactivity, comparable to that of high α-TGIC. The reactivity of the matrix is higher than that of the powder.

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