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Avramidis, Georg

Surface Analytics of Atmospheric Pressure Plasma Treated Wood and Wood-Based Materials

1. Auflage, Juli 2015
Englisch, 190 Seiten, 14,8 x 21 cm, 260 g
ISBN: 978-3-86844-727-9
38,00 €
ODER
Surface Analytics of Atmospheric Pressure Plasma Treated Wood and Wood-Based Materials

Schlagworte

plasma, wood, surface energy, XPS, impregnation, plasma polymerisation

Das Buch

The aim of this work is to examine the altered surface characteristics of wood and wood-based materials either by air plasma treatment or plasma-based deposition of hydrophobic  layers using DBD-configurations at atmospheric pressure.

Contact angle measurements and surface energy determination of air plasma-treated wood material  have shown increased polar part of surface energy and improved wetting characteristics of these  surfaces in general. The mechanisms of these consequences of air plasma treatment were investigated by means of surface sensitive XPS-analysis. It was demonstrated for beech wood that freshly exposed surfaces show a distinct increase in oxygen-bonded carbon components compared to aged wood surfaces, outperformed by air plasma-treated surfaces. The decreasing differences in the O/C-ratio of untreated and air plasma-treated samples with increasing storing duration as well as the differences of the O/C-ratio compared to theoretical and micro- analytical values can be attributed to the surface allocation of environmental contaminants and the surface migration of wood extractives.
The degradation of solvent and water-soluble extractives could also be demonstrated with XPS. This led to the assumption that not only the creation of functional groups can be responsible for enhanced wetting characteristics but also the air plasma based exposure of hydrophilic (compared to extractives) wood structures can participate to increased surface energy.
Beech wood impregnated with wax showed a significantly increased polar part of surface energy and an improved adhesion for PVAc-glued samples after prolonged air plasma treatment. No increase in bonding strength could be detected when applying EPI and phenol-resorcinol glues. Time-dependent shear strength tests showed accelerated curing of PVAc-glued hardwood veneers when air plasma-treated. This was attributed to an increased penetration of water into the bulk material and thus loss of water within the bond line.
Acceleration of liquid uptake (water, DMDHEU, melamine resin) after air-plasma treatment could be demonstrated for beech veneers, thermally treated beech veneers and (with restrictions) oak veneers. No improvement in water uptake could be detected for the softwoods (pine and spruce).

Hydrophobic layers on wood surfaces were deposited by plasma polymerisation usingethylene or HMDSO as a chemical precursor.

Ethylene-based layers deposited on wood surfaces by plasma polymerisation showed distinct hydrophobic properties with a WCA value around 110°. It could be demonstrated that operating parameters such as the Ar/C2H4-ratio and the injected power to the discharge are parameters which control the resulting WCA although the chemical composition, analysed by FTIR-spectroscopy, is only marginally influenced. HMDSO-based layers were deposited on wood surfaces using a planar plasma-set-up and the effluent of a special plasma system. The O2/HMDSO-ratio as well as the injected power influences the chemical and physical properties of the deposited layers. It turned out that the use of the plasma-effluent creates homogeneous layers delaying water drop absorption up to ten times in comparison to the layers created by the planar set-up. The micro-topographic features of the deposited layers were analysed by AFM revealing a structure with periodic texture in the µm-range as well as sub-textures in the nm-range.



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