Water-based Polyurethanes

With new regulations appearing around the country that limit the amounts of volatile organic compounds (VOCs) allowed in paints and varnishes, a host of new products are appearing on the market. This is especially true with varnishes, where new “environmental” polyurethanes are being introduced that use water as the carrier instead of petroleum-based solvent. Manufacturers of these products promote them as being environmentally friendly and chemically resistant. What are the benefits of water-based polyurethane varnish, and what are the limitations? Results of informal trials of water-based polyurethanes by EBN contributing editor Dan MacArthur are reported on below.

Water-based polyurethanes do contain VOCs, so they cannot be considered environmentally benign. VOCs are used in water-based polyurethane to keep the solid polymers that will eventually bind into a finish suspended in water, and to help the solids harden as the solvent evaporates. Legislation controlling VOC content varies around the country, but most companies are formulating their finishes to comply with California regulations, which allow up to 450 grams per liter of VOCs in solvent-based polyurethane and up to 350 grams per liter in water-based polyurethane.