Water sorption in UV degraded clear and pigmented epoxy coatings assessed by dielectric sorption analysis

Degraded clear and pigmented epoxy coatings were investigated by dielectric sorption analysis (DSA). Differences in dynamics of absorption, due to increased hydrophilicity, crosslinking and porosity, were found between UV degraded and undegraded epoxy coatings. Desorption was observed for longer degradation times, caused by swelling of the coating, squeezing out the excess of water. Model system measurements of pigmented coatings with various filters on top reproduced the desorption behaviour. Due to crack formation during DSA measurements, clear coatings showed fluctuating results, a result of release of tension of the UV degraded clear coating by humidified nitrogen. Pigmented coatings did not show this behaviour, resulting in an increasing water absorption trend with increasing degradation times. Larger desorption peaks were found for lower frequencies, indicating that either polarization takes place or water-hydrophilic interaction. Based on these results, DSA is suitable for non-destructive investigation of degraded coatings and paints.