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.
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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