UBC Theses and Dissertations
Etching of wood by glow-discharge plasma Jamali, Arash
In this thesis I hypothesize that plasma will etch wood surfaces, produce new cell wall microstructures, and change the surface chemistry of wood because of differential etching of wood’s polymeric constituents. I also examine factors affecting the etching of wood by plasma, and applications of plasma etching for wood processing. Scanning electron and light microscopy and white light confocal profilometry were used to examine etching of wood surfaces. Wet chemical analysis, FTIR and XPS spectroscopy were used to analyze chemical changes at the surface of plasma-treated wood. Experiments were also performed to examine the effect of plasma treatments on the color of blue-stained wood, the morphology of fungal hyphae and the adhesion and performance of coatings on hot-oil modified wood. Exposure of wood to plasma caused etching of wood cell walls and created new surface microstructures. Regions of cell walls that were rich in lignin such as the middle lamella were etched more slowly by plasma. Confocal profilometry of wood exposed to plasma revealed a strong relationship between plasma treatment time and etching of cell walls, and same technique found that lignin pellets were etched more slowly than cellulose pellets. Plasma reduced the levels of carbohydrate at the surface of modified wood, which resulted in a relative increase in lignin content. Plasma treatment improved the effectiveness of hypochlorite bleach at removing blue-stain from wood and it prevented the discoloration of a white acrylic paint on hot-oil modified wood exposed to natural weathering. However, plasma treatment of hot-oil modified wood did not have positive effects on the adhesion and exterior performance of a range of other coatings (mainly semi-transparent stains). I conclude that prolonged exposure to plasma can etch wood cell walls, but cell wall layers that are rich in lignin are degraded more slowly. Plasma etching of wood mainly depends on treatment time and also on the structure and chemical composition of wood. Plasma treatment is an efficient pre-treatment for bleaching of blue-stained wood and reducing the discoloration of white acrylic paint on hot-oil modified wood.
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