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Issue 2, 2013
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Banning toxic heavy-metal catalysts from paints: enzymatic cross-linking of alkyd resins

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Abstract

Alkyd resins are polyesters containing unsaturated fatty acids that are used as binding agents in paints and coatings. Chemical drying of these polyesters is based on heavy metal catalyzed cross-linking of the unsaturated fatty acid moieties. Among the heavy-metal catalysts, cobalt complexes are the most effective, yet they have been proven to be carcinogenic. Therefore, strategies to replace the cobalt-based catalyst by environmentally friendlier and less toxic alternatives are under development. Here, we demonstrate for the first time that a laccase–mediator system can effectively replace the heavy-metal catalyst and cross-link alkyd resins. Interestingly, the biocatalytic reaction does not only work in aqueous media, but also in a solid film, where enzyme diffusion is limited. Within the catalytic cycle, the mediator oxidizes the alkyd resin and is regenerated by the laccase, which is uniformly distributed within the drying film as evidenced by confocal laser scanning microscopy. During gradual build-up of molecular weight, there is a concomitant decrease of the oxygen content in the film. A new optical sensor to follow oxygen consumption during the cross-linking reaction was developed and validated with state of the art techniques. A remarkable feature is the low sample amount required, which allows faster screening of new catalysts.

Graphical abstract: Banning toxic heavy-metal catalysts from paints: enzymatic cross-linking of alkyd resins

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Publication details

The article was received on 19 Oct 2012, accepted on 21 Dec 2012 and first published on 21 Jan 2013


Article type: Paper
DOI: 10.1039/C2GC36666E
Green Chem., 2013,15, 381-388

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    Banning toxic heavy-metal catalysts from paints: enzymatic cross-linking of alkyd resins

    K. J. Greimel, V. Perz, K. Koren, R. Feola, A. Temel, C. Sohar, E. Herrero Acero, I. Klimant and G. M. Guebitz, Green Chem., 2013, 15, 381
    DOI: 10.1039/C2GC36666E

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