Emission of glycol ethers from medium-density fibreboard surfaces coated by a waterborne lacquer under different drying conditions

Abstract

The use of waterborne coatings has become increasingly popular in the furniture industry, as the use of organic solvents is going to be restricted according to a European Union directive. Waterborne coatings commonly need the use of up to 15% organic solvents to achieve proper film formation. The chemicals used usually have a lower vapour pressure than common solvents and may cause elevated emissions of volatile organic compounds (VOCs) during the first few weeks. This article describes the influence of temperature and relative humidity (RH) on later VOC emission during the lacquer drying of medium-density fibreboard. Twenty-seven boards were lacquered with a common industrial waterborne clear lacquer and dried under climatic conditions ranging from 20°C to 40°C, and 20% to 80% RH. The emission of VOCs was measured using a field and laboratory emission cell at 24 h, 72 h, 10 days and 28 days after drying. The cosolvents 2-butoxyethanol and 2-(2-ethoxyethoxy)ethanol were found. Their emission rates ranged from 400 to 16,000 µg m⁻³. Boards dried at a higher temperature emitted significantly less than those dried at 20°C. Drying at high RH resulted in lower emission levels than drying at low RH. This is explained by a higher mass transfer between the liquid lacquer phase and the air. If the lacquer film is kept wet for a longer period, the organic cosolvent reservoir can be depleted during a longer time. These findings agree with the concept of critical RH derived by Dillon [Journal of Coatings Technology, 1977, 49(634), 38].

Keywords:

• Volatile organic compounds
• glycol ethers
• critical relative humidity