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A surprisingly simple and rapid methodology for large-area, lightweight, and thin laminate coatings with remarkable moisture barrier properties is introduced. Commercially available paperboards are coated with thin layers of nanocellulose. The nanocellulose coating induces a surface smoothening effect on the coated sheets as characterized by environmental scanning electron microscopy and white light interferometry. A moisture-protective layer of renewable alkyd resins is deposited on the nanocellulose precoated sheets using a water-borne dispersion coating process or lithographic printing. Through an auto-oxidation process, the applied alkyd resins are transformed into moisture sealant layers. The moisture barrier properties are characterized in detail by water vapor permeability measurements at different levels of relative humidity. The water vapor barrier properties of the nanocellulose precoated substrates were significantly improved by thin layers of renewable alkyd resins. The effect of the alkyd resin properties, coating technologies, and base paper substrates on the final barrier performance of the sheets were studied. It was found that the nanocellulose coating had a notable effect on the homogeneity and barrier performance of the alkyd resin layers and in particular those alkyd resin layers that were applied by printing. The concept is environmentally friendly, energy-efficient, and economic and is ready for scaling-up via continuous roll-to-roll processes. Large-scale renewable coatings applicable for sustainable packaging solutions are foreseen.

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Hydrogen and oxygen plasma treatment of two cellulose materials, a filter paper of pure cellulose and a greaseproof paper with a fairly high surface content of wood resin, has been studied with ESCA as well as by contact angle or water absorption. The hydrogen plasma treatment reduces the hydroxyl groups on the cellulose and creates low molecular weight materials. Due to the lower polarity, water absorption is reduced. The oxygen plasma treatment of the pure cellulose both oxidizes and reduces the surface. The resin-rich paper, which has a hydrophobic nature, shows improved water wettability after both hydrogen and oxygen plasma treatments.

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This work focuses on the determination of apparent contact angles on wood by the Wilhelmy method. In this method, the force acting on an object is measured during a test cycle involving immersion in and withdrawal from a probe liquid. Fresh and aged veneers of extracted and non-extracted heart-and sapwood of pine were investigated. The results indicate that wicking of the probe liquids, into and along the porous wood veneers, occurs during the test cycles and that this strongly affects the determination of contact angles. It is suggested that two different wicking phenomena occur. First, when the veneer contacts the liquid, an instantaneous 'initial wicking' occurs. It is suggested that this initial wicking is influenced primarily by the liquid density and structural properties of the specimen (such as porosity and surface roughness), and not by surface energetics. An initial wicking constant was therefore estimated for the different veneer samples based on measurements in octane. Second, after the initial wicking, a continuing 'secondary wicking' is observed. In some cases, this may result in zero contact angle after a certain immersion depth. Contact angles should, therefore, be estimated from the initial part of the immersion, where the secondary wicking can be neglected. This may also reduce any contamination of the probe liquids by extractives. The Wilhelmy method seems to be a valuable tool for estimating the wetting properties of wood, permitting reproducible measurements of apparent contact angles provided that there is efficient control of wicking and contamination effects. KeywordsApparent contact angles Contamination Extractives Wettability Wicking Wilhelmy method Wood Brought to you by | University of Arizona Authenticated Download Date | 5/26/15 5:35 PM