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Journal of Coatings Technology and Research

, Volume 15, Issue 6, pp 1273–1282 | Cite as

Photooxidative stability provided by condensed tannin additives in acrylic-based surface coatings on exterior exposure

  • W. J. Grigsby
Article
  • 106 Downloads

Abstract

Condensed tannins, also known as proanthocyanidins, have been added as functional additives to acrylic-based clear coatings to promote polymer coating longevity and also stabilize timber color on accelerated and exterior weathering. When added at < 0.5% w/w content, native tannins and tannins modified with maleate groups extended coating performance > 20% compared to commercial hindered amine light stabilizers (HALS) and phenolic stabilizers used at comparable coating loadings. Other tannin chemical modifications such as methylcarboxylate groups were also associated with greater coating longevity beyond that achieved with the synthetic UV and antioxidant additives. This study has also revealed that tannin addition to acrylic coatings can act to photostabilize timber coloring on exterior exposure. While tannin use can contribute color to coatings, any color was rapidly bleached on UV exposure with a dependency on tannin content, degree of modification, and coating formulation pH. Moreover, through manipulating tannin addition levels, this tannin decolorization could offset typical wood darkening associated with UV exposure to provide low or no wood color change over longer exposure periods. With the photooxidative stability efficacy of tannins established on exterior exposure, condensed tannins in native and modified form offer potential as sustainable functional additives for the coatings sector.

Keywords

Condensed tannins Proanthocyanidins Functional additives Coatings Acrylics Styrene acrylics Exterior exposure Weathering 

Notes

Acknowledgments

This work was supported by Biopolymer Network Ltd, through funding by the New Zealand Ministry of Business, Innovation and Employment.

Supplementary material

11998_2018_86_MOESM1_ESM.docx (879 kb)
Supplementary material 1 (DOCX 879 kb)

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Copyright information

© American Coatings Association 2018

Authors and Affiliations

  1. 1.Biopolymer Network Ltd and ScionRotoruaNew Zealand

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