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Delayed access 60 months for the original version. Access for registered users. The objective of this work is to study the water vapor sorption and surface energy properties of thermally modified wood (TMW) components, ie wood processing residuals in the form of sawdust. The thermal modification was performed on spruce wood components using a steam-pressurized laboratory-scale reactor at two different temperature (T) and relative humidity (RH) conditions, T ¼ 150°C and RH ¼ 100% (TMW150), and T ¼ 180°C and RH ¼ 46% (TMW180). A dynamic vapor sorption (DVS) technique was used to determine water vapor sorption isotherms of the samples for three adsorption-desorption cycles at varying RH between 0% and 95%. Inverse gas chromatography (IGC) was used to study the surface energy properties of the samples, including dispersive and polar characteristics. The DVS results showed that the EMC was reduced by 30-50% for the TMW samples compared with control samples of unmodified wood (UW) components. A lower reduction was, however, observed for the second and third adsorption cycles compared with thatof the first cycle. Ratios between EMC of TMW and that of UW samples were lower for the TMW180 compared with the TMW150 samples, and an overall decrease in such EMC ratios was observed at higher RH for both TMW samples. The IGC results showed that the dispersive contribution to the surface energy was higher at lower surface coverages, ie representing the higher energy sites, for the TMW compared with the UW samples. In addition, an analysis of the acid-base properties indicated a higher KB than KA number, ie a higher basic than acidic contribution to the surface energy, for all the samples. A higher KB number was also observed for the TMW compared with the UW samples, suggested to relate to the presence of ether bonds from increased lignin and/or extractives content at the surface. The KB was lower for TMW180 compared with TMW150, as a result of higher modification temperature of the first, leading to cleavage of these ether bonds.

This study investigated the morphologic and chemical properties of coatings based on PMMA/ATH powder and deposited by cold plasma spraying on wood and glass. Since the deposition of pure PMMA/ATH powder with air as process gas yielded coatings with insufficient abrasion resistance, two modifications of the basic process were investigated. Previous studies showed that replacing air as process gas with forming gas did not enhance the abrasion resistance, but the addition of a phenol-formaldehyde resin (PF) succeeded in stabilising the particle coatings. In this work, results from morphologic and chemical analysis suggested an encasement of the PMMA/ATH particles by plasma-modified PF and thus a fusion of individual particles, explaining the enhanced bonding. Moreover, adhesion tests confirmed an outstanding bonding between the coating and wood as well as glass, which is assumed to result from interactions between the PF’s hydroxyl groups and functional groups on the substrates’ surfaces. Studies on the wettability revealed a hydrophobic character of such coatings, therefore generally indicating a possible application, for example, to reduce water uptake by wooden materials.

Thermally modified and unmodified beech veneers in untreated and plasma-treated state were immersed in melamine solution at different concentrations. The plasma pre-treated veneers exhibited significantly higher melamine loads than the untreated veneers at equal impregnation duration. Subsequently the veneers were manufactured into 5-layer plywood boards; the plywood samples then underwent an extreme testing procedure based on DIN-EN 314-1/2 in order to proof the bonding quality by means of shear strength. The plywood boards made of plasma pre-treated veneers exhibited up to 2.7-fold improvement in shear strength compared to plywood made of untreated veneers. Results differed markedly based on material (unmodified/thermally modified veneer) and concentration of melamine solution.

Atmospheric pressure plasma was used to deposit thin layers of copper and aluminium micro-particles on the surface of Scots pine sapwood (Pinus sylvestris L.) boards. Three different loadings of metal particles were established. Additional wood boards were topcoated with a commercial acrylic binder. Boards were exposed to natural weathering for 18 months. Discolouration of copper-treated boards was slowed down, and the treatment at highest loading displayed the best appearance. Aluminium treatment was not sufficient to prevent or reduce discolouration. The application of an acrylic binder as topcoating enhanced the general appearance of metal-treated boards. Evaluation of treated boards did not reveal any reduction in crack formation or water uptake due to the particle deposition. Infrared spectroscopy suggested that copper does not protect lignin from photo-degradation. Nevertheless, copper treatment reduced fungal infestation on wood; at highest copper loading, blue stain did not penetrate through the treated surface.

Scots pine (Pinus sylvestris L.) sapwood specimens were subjected to a two-step treatment combining vacuum-pressure impregnation with short-chain siloxanes followed by copper deposition on the wood surface via atmospheric pressure plasma. The obtained materials were exposed to a blue stain fungus in a laboratory test following EN 152 (2011). Copper treatment alone reduced fungal colonisation, but did not fully prevent it. A two-step treatment was able to impart high resistance to Aureobasidium pullulans. Termite resistance of siloxane-treated and copper-plasma coated wood was also assessed. A laboratory no-choice test according to EN 118 (2013) revealed strong attack by Reticulitermes flavipes, but termite mortality increased compared to untreated wood. In contrast, under choice conditions, R. flavipes exhibited significant avoidance towards the treated specimens.