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UBC Theses and Dissertations

Molten wax spray treatment makes oriented strandboard (OSB) more water repellent and reduces thickness swelling Lotter, Barend Theron

Abstract

When oriented strandboard (OSB) absorbs moisture its compressed wood strands swell up and recover strains that were induced during hot pressing. Adhesive bonds that hold the strands together rupture and permanent thickness swelling occur. Few post-treatments are able to effectively reduce the thickness swelling of OSB. OSB is porous, with inter-strand voids up to 1.5 mm in diameter. Surface coatings are less effective at restricting moisture ingress into OSB than into solid wood, because of the irregular surface of OSB. Molten wax has a low viscosity and may be able to flow into and block the inter-strand voids of OSB. In this thesis I hypothesize that the water repellency and dimensional stability of OSB may be improved by spraying molten wax onto the hot surface of the board. Furthermore, I hypothesize that polar and low melting point waxes will form more effective water repellent barriers than nonpolar or high melting point waxes. The properties of 13 different waxes and five custom made wax blends were characterized with emphasis on properties likely to influence the water repellency of OSB. Molten waxes were sprayed onto the surface of hot OSB and the water absorption and thickness swelling of the samples were measured. Wax treatments were able to reduce the rate of water absorption and the rate of thickness swelling, but not the extent thickness swelling. I conclude that wax treatments are able to increase the water repellency of OSB and reduce the thickness swelling during short-term periods of exposure to water. Waxes with high melting point temperatures tended to form more effective water-repellent barriers, especially for short-term exposure periods, contrary to my hypothesis. Blends of pure beeswax, which contains polar functional groups, and strongly hydrophobic waxes, such as paraffin wax, formed excellent water-repellent barriers. The results suggest that a combination of polar and nonpolar wax is more effective at reducing the thickness swelling of wax-treated OSB than waxes that contain only hydrophobic components. Errata: http://hdl.handle.net/2429/46708.

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Attribution-NonCommercial-NoDerivs 2.5 Canada