Surfactant-free carnauba wax dispersion and its use for layer-by-layer assembled protective surface coatings on wood

Author

AlinaLozhechnikovaaHervéBellangerbcBenjaminMichenbcIngoBurgertbcMonikaÖsterberga

a

Department of Forest Products Technology, School of Chemical Technology, Aalto University, P.O. Box 16300, FI-00076, Aalto, Finland

b

Institute for Building Materials (IfB), Wood Materials Science, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland

c

Applied Wood Materials Laboratory, Empa − Swiss Federal Laboratories for Material Testing and Research, 8600 Dübendorf, Switzerland

Received 3 October 2016, Revised 15 November 2016, Accepted 18 November 2016, Available online 18 November 2016.

Highlights

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A facile sonication route to produce aqueous wax dispersions is developed.

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The wax dispersion is naturally stable and free of surfactants or stabilizers.

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Wax and ZnO particles are coated onto wood using layer-by-layer assembly.

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The coating brings superhydrophobicity while preserving moisture buffering.

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ZnO improves the color stability of wood to UV light.

Abstract

Protection from liquid water and UV radiation are equally important, and a sophisticated approach is needed when developing surface coatings that preserve the natural and well-appreciated aesthetic appearance of wood. In order to prevent degradation and prolong the service life of timber, a protective coating was assembled using carnauba wax particles and zinc oxide nanoparticles via layer-by-layer deposition in water. For this purpose, a facile sonication route was developed to produce aqueous wax dispersion without any surfactants or stabilizers. The suspension was stable above pH 4 due to the electrostatic repulsion between the negatively charged wax particles. The particle size could be controlled by the initial wax concentration with average particle sizes ranging from 260 to 360 nm for 1 and 10 g/L, respectively. The deposition of wax particles onto the surface of spruce wood introduced additional roughness to the wood surface at micron level, while zinc oxide provided nano roughness and UV-absorbing properties. In addition to making wood superhydrophobic, this novel multilayer coating enhanced the natural moisture buffering capability of spruce. Moreover, wood surfaces prepared in this fashion showed a significant reduction in color change after exposure to UV light. A degradation of the wax through photocatalytic activity of the ZnO particles was measured by FTIR, indicating that further studies are required to achieve long-term stability. Nevertheless, the developed coating showed a unique combination of superhydrophobicity and excellent moisture buffering ability and some UV protection, all achieved using an environmentally friendly coating process, which is beneficial to retain the natural appearance of wood and improve indoor air quality and comfort.

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