Determination of the relative activity of selected paint stripping components with epoxy and polyurethane aerospace coatings

Throughout the aerospace industry protective coatings are applied to finished parts, components, and even the entire aircraft. However, coatings must be periodically removed to conduct inspections, repairs, or to replace the coating itself and also to smarten the corporate identity of the aircraft. The solvents employed in this operation contain some components considered to be hazardous, both to humans and the environment. The development of alternative, environmentally acceptable chemical paint strippers was therefore necessary. To achieve this fit, it is desirable to develop a sound, scientific understanding of how traditional chemical paint strippers work. The focus of this study was to investigate methods of measuring the performance of specific paint stripper components and to determine the relative activity of primary components in a model chemical paint stripper, with epoxy and polyurethane aerospace coatings, with emphasis on methylene chloride, phenol, ethanol and water. The specific methods investigated include volume swell of the coatings, a measure of the overall strength of interaction between the coatings and solvents, along with the extent and rate of debonding, a measure of the effectiveness of each component as a paint stripper. Optical dilatometry was used to observe the rate and extent of volume swell of the coating materials. Additionally, a unique optical system directly observed how the coatings debond from a model aluminum oxide substrate. Overall, the results of these three methods are consistent, showing that water in combination with phenol is the most active, followed by water with ethanol, phenol, ethanol, and methylene chloride being the least. As a solvent system, these results suggest that methylene chloride serves primarily as a penetrant and carrier for the other solvent components. Water serves as an activator, with phenol and ethanol serving as the active solvents or activated species in the solvent system during the stripping process