We hypothesize that plasma will etch wood and fungal hyphae in blue-stained lodgepole pine, and increase the ability of hypochlorite bleach to remove discolouration from blue-stained wood. Blue-stained lodgepole pine wood was exposed to a glow-discharge plasma derived from water, and the surface wettability, permeability and colour of the treated wood was measured. Plasma-treated wood was dipped in sodium hypochlorite bleach and the colour of the blue-stained wood was re-measured. Scanning electron and light microscopy was used to observe changes in the microstructure of plasma-treated blue-stained wood. We collected hyphae from the blue-stain fungus Grosmannia clavigera and used scanning and transmission electron microscopy to examine the effects of plasma on the structure of fungal hyphae. Plasma treatment increased the wettability and permeability of blue-stained lodgepole pine sapwood and removed some of the blue-discolouration from the wood. Plasma modified the microstructure of lodgepole pine wood by etching bordered pits and cell walls at wood surfaces. Bleaching of blue-stained wood by sodium hypochlorite bleach was significantly improved by plasma pre-treatments. The effectiveness of the plasma pre-treatment at removing blue-stain was influenced by the duration of the treatment. Plasma etched hyphal walls of the blue-stain fungus and degraded melanin. Our results demonstrate that plasma treatments are able to remove the discolouration from blue-stained wood, and increase the effectiveness of a bleaching agent because they degrade and remove blue/black fungal hyphae, open-up bordered pits and enable more of the bleach to be absorbed by wood. The development of plasma etching devices capable of operating at high speed and atmospheric pressure are needed to develop plasma-assisted bleaching processes that can be used commercially to remove fungal staining from wood.

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