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Environment

Metal-Free Cure For Paints And Coatings

Study shows that enzymes can serve as green replacements for metal-based catalysts used to cross-link alkyd resins

by Stephen K. Ritter
February 4, 2013 | A version of this story appeared in Volume 91, Issue 5

Alkyd resins are polyesters commonly used as binding agents in paints and coatings. When exposed to air, the polyesters cross-link with the assistance of a metal catalyst, in particular cobalt complexes. The process assists in curing the coating to a smooth finish. In an effort to avoid toxicity associated with the metal catalysts, a team led by Enrique Herrero Acero of the Austrian Centre of Industrial Biotechnology has for the first time shown that enzymes are up to the task of catalyzing the cross-linking (Green Chem., DOI: 10.1039/c2gc36666e). The researchers selected a laccase enzyme already used in food and other industries to snatch oxygen from the air and oxidize 1-hydroxybenzotriazole. The oxidized mediator molecule then extracts hydrogen atoms from polyester double bonds to instigate the cross-linking. The development comes at a time when consumer awareness is pressing the coatings industry to develop low-toxicity green alternatives to cobalt catalysts. Enzyme-based curing could help manufacturers avoid anticipated new regulations that would force them to register, classify, and label cobalt-containing coatings.

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