RESISTANCE TO WATER AT 100-DEGREES-C OF UNSATURATED POLYESTER COATINGS AS A FUNCTION OF THEIR STATE OF CURE - MODELING THE PROCESS OF CURE AND POSTCURE, AND OF DIFFUSION

The resistance to water at 100 degrees C of unsaturated polyester coat ings is evaluated by determining the kinetics of absorption of water. The process is controlled by Fickian diffusion as found from experimen ts and thus two parameters are necessary to characterize the stage of absorption, the diffusivity and the amount of water absorbed at equili brium. The state of cure, expressed by the heat evolved by the cure re action in the mould as a fraction of the total cure enthalpy, is corre lated with the resistance to water at 100 degrees C for thermosets. Th e state of cure of the resin is calculated by using a numerical model taking into account heat conduction and heat evolved by the cure react ion. Good correlation is obtained, showing that a high value of the st ate of cure for a thermoset is associated with a lower diffusivity and lower amount of water absorbed, or in other words with a higher resis tance to water. However, an increase in the state of cure is calculate d during the test at 100 degrees C.