Dielectric sorption analysis of pigmented epoxy coatings UV degraded at elevated pressures

Pigmented epoxy coatings were UV degraded for various periods at elevated pressures (1-100 bar) and investigated with dielectric sorption analysis (DSA). Differences in dynamics of absorption behaviour for degraded polymer occurred due to increased hydrophilicity, crosslinking and porosity. Degradation at all pressures showed desorption, caused by swelling of the coating and shrinking of pore size. The amount of water sorption and desorption rose linearly from 1 bar to 50 bar and from 50 bar on no further increase in degradation was found. Longer degradation times at 100 bar also resulted in a linear trend. At lower frequencies double peaks were found as a result of water desorption, polymer relaxation, water-hydrophilic cluster interactions and polymer swelling, indicating a frequency dependence. The double peak could be fitted by two independent curves, whereas a single exponential term sufficed to fit the desorption of water for all frequencies. Pressure is clearly an accelerating degradation parameter in combination with an UV source.