Interim Report on Scientific Basis for Paint Stripping: Mechanism of Methylene Chloride Based Paint Removers

摘要

Chemical paint strippers that include methylene chloride and phenol have been extensively used to remove polymer coatings from metallic substrates. These strippers are inexpensive and remove polymeric organic coatings quickly and easily from a variety of metallic substrates without damage to the substrate. However, due to environmental and health concerns there is increasing pressure to replace methylene chloride with less hazardous alternatives. Although various alternatives to these organic solvent based systems have been developed, none equal their effectiveness in performance or cost. Thus far the mechanism of action of chemical strippers has not been adequately characterized. In order to experimentally determine the paint removal mechanisms of methylene chloride, it was important to first limit the variables in the overall process. Many of the more prominent variables exist in the coating itself, and therefore the development of simplified formulations (clear films) of each coating of interest is a logical starting point. Herein we report changes in physical and molecular-level properties of four polymer coatings upon exposure to components of the paint stripper including methylene chloride and phenol. The coatings studied were clear films of polyurethane topcoats and epoxy primers currently in military use. Using proprietary information supplied by a paint supplier, we combined the resin binders and curing agents as specified to attempt to produce clear coat films. Initial attempts failed because it was learned that the pigments and extenders provided beneficial effects in the curing process. For example, the extenders allow more expedient outgassing by providing pathways for gas to escape. To compensate for this, significant modifications to the original formula were necessary to affect flow characteristics in order to facilitate the creation of a continuous smooth film.