Morphological Changes in Exterior Exposure to Cyclic and Ultraviolet Surface Coatings After Water Submersion Exposure

By Armin Burghart, Sridhar G. Iyer, William J. Rosano

Exterior surface coatings used in many applications can be exposed for long periods of time to cyclic exposure consisting of water submersion or local water surface puddling followed by water evaporation and solar exposure. Under such conditions, several macroscopic defects can appear including blistering, adhesion loss, soil pick-up, cracking, erosion, etc.

However, quite often surface microscopic film defects can start long before these macroscopic defects are visibly evident. In this article, we show surface microscopic morphology changes to coatings cycled between water (submersion) and ultraviolet (UV) expo-sure where both polymer and formulation compositional factors were explored.

Scanning electron microscopy (SEM) showed microscopic defects such as polymer-filler separation, filler removal, and degradation and crack formation appearance after short-term (one month) cyclic testing. The micrographs also revealed that the observed film defects were confined to the exposed surface and about a few filler particle diameters deep.