Determination of concentrations of acetic acid emitted from wood coatings in enclosures

Twenty-two commercial coatings were chosen, based on their film-forming mechanisms, to study the equilibrium concentrations of volatile organic compounds (VOCs) and their emission rates at steady state. Concentrations of acetic acid (ethanoic acid) and total VOCs were measured using a thermal desorption unit coupled with a gas chromatograph. Almost all coatings released acetic acid, but at different rates. Coatings formed by oxidative polymerization were found to generate a high level of acetic acid at both equilibrium and steady state. The acetic acid equilibrium concentrations from the coatings formed by the other types of mechanism studied tended to be similar to those from red oak, an acidic wood. In a steady-state situation, most of the coatings applied on aluminium or on red oak had acetic acid emission rates lower than that of red oak alone, with the exception of the red oak coated with pigmented films formed by coalescence. The wide range of acetic acid equilibrium concentrations and emission rates for films formed by coalescence is due to the mixture of porous resin, extenders and free acetic acid in the formulations. Consideration should be given to allowing a sufficient drying period (three to four weeks) before using coated enclosures, in order to reduce the VOC concentrations within the enclosures.