Transfer inovácií 20/2011 2011 33 Ing. Igor Novák, PhD. 1 Ing. Vladimír Vanko 2 Ing. Jozef Preťo 2 Prof. Ing. Ivan Chodák, DrSc. 1 Ing. Anton Popelka 1 Doc. Ing. Ján Sedliačik, PhD. 3 Ing. Vladimír Pollák, PhD. 1 1 Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 41 Bratislava, Slovakia 2 VIPO, a.s., Gen. Svobodu 1069/4 958 01 Partizánske, Slovakia 3 Technical University in Zvolen T. G. Masaryka, Zvolen, Slovakia e-mail: upolnovi@savba.sk Abstract The atmospheric discharge plasma has been used to improve the wetting and adhesion properties of wood. The low-temperature plasma processes are attractive for wood industry applications because of their lower cost, and ability to operate in-line without vacuum systems. However, using the sessile droplet technique, we have identified a significant increase of polar component of surface free energy. Polar part of surface free energy is associated with the presence of acid/base forces (electron donor–acceptor bonds). The treatment of wood exhibited a substantial aging effect; nevertheless the treated surface never recovers to its initial hydrophobic state. The enhancement of wood wettability is a necessary condition to promote a better adhesion with a water-based adhesives and coatings, which is currently being studied. Key words: surface modification, plasma discharge, contact angle INTRODUCTION The bonding of wood after electric discharge plasma surface modification is of considerable interest with the respect to construction of the strongest wood adhesive joints (1 -3). Great efforts have been made in developing various kinds of furniture using plastic or wood veneers in adhesive joints wood-adhesive-veneer. The coplanar surface barrier plasma at atmospheric pressure is currently the most promising methods of surface modification, and are considered as the ‘green’ ecologically friendly modification method (4). For a common industrial wood application various woods have to possess a large set of various surface characteristics, including polarity (hydrophobicity or hydrophilicity), dyability, scratch resistance, tailored adhesive properties, antibacterial resistance etc. Nanoscale changes to the surface of wood materials enable the changes in materials surface, while maintaining the desirable bulk material properties. EXPERIMENTAL MATERIALS Wood boards, wood particles (oak) (TU Zvolen, Slovakia), ChS Epoxy 510 (Czech Republic), testing liquids (water, ethylene glycol, formamide, diiodmethane, 1-bromnaphthalene, dischlormetane. MODIFICATION METHOD In this paper the modified wood filler/particles (d < 50 micrometer) were investigated using diffuse coplanar barrier surface discharge (DCSBD) plasma of selected wood kind (oak wood particles), for potential applicability in woodworking industry. The selected wood was modified by DCSBD plasma. There are two reasons why in the case of wood to apply plasma discharge modification. Firstly, plasma in air itself significantly increases hydrophilicity of the wood surface, because of formation various polar groups (e.g. hydroxyl, carbonyl, carboxyl, etc), and, the wood macromolecules are also cross-links (up to a few microns) what leads to the increase in scratch resistance and to the improvement in barrier properties of the wood material. Second reason for the plasma use is to increase adhesion in adhesive joint between wood particles in fiberboard material, or wood-wood and/or wood-polymer (e.g. polyvinylchloride, other plastic foils) for industrial applications due to growth of wood wettability. Scheme 1 Source of DCSBD plasma for wood modification Plasma modification was implemented in static conditions by DCSBD plasma technology (Fig. 1) of laboratory scale with oxygen as the gaseous medium at atmospheric pressure and room temperature. A schematic profile of the plasma system is given in Scheme 1. It basically comprises a series of parallel metallic electrodes inset inside a ceramic dielectric located in a glass chamber, which allows the carrier gases to flow. All samples were MODIFICATION OF WOOD BY ATMOSPHERIC DISCHARGE PLASMA