Formulation Strategies Using Exempt Solvents: Latest Developments
Fortunately, over the last seven years or so, a few more practical coating solvents have been exempted from categorization as VOCs by the EPA.1 Unlike the chlorinated materials noted above, none of these materials are either ozone depletors or HAPs. As VOC-exempt solvents, these materials may be used in coatings, but are excluded from the weight aggregation of total VOC although, like water, their volume must also be excluded from the VOC calculation. In effect, these solvents may be added to a given formulation without restriction, reducing viscosity and, therefore, improving application without affecting the VOC content of the formulation. They may even be added with impunity by applicators in the field.2 The exemption, of course, does nothing for volume solids, which are progressively reduced with exempt solvent additions.
This, along with its low cost, are the primary advantages for acetone. Aside from its flammability (TCC flash point -4ºF) and an extremely fast evaporation rate which severely limits the quantity of acetone which may be practically employed in any given formulation, its main drawback is its ketonic reactivity (hydrogen acceptance) with certain mainstream binders (epoxy curing agents). Its very low boiling properties also result in a tendency to induce blushing and may cause problems with urethane systems. Ketonic residues retained in an applied film may also detract from that film’s weatherability.