Evaluation of Dynamic Contact Angle of Loose and Tight Sides of Thermally Compressed Birch Veneer

Rotary-cut veneer is characterised by two sides, namely loose and tight surface, which have different properties. The information concerning dynamic contact angle behaviour of veneer sides plays an important role in efficient use of veneer. Therefore, the objective of this study was to investigate the influence of different compression temperatures and pressures on various wetting behaviour of loose and tight sides of birch veneer. Veneer sheets were compressed in a hot press at temperatures of 150 and 180 °C using seven pressure levels from 0.5 to 3.5 MPa. Wettability of loose and tight sides of thermally compressed veneer was evaluated by measuring the dynamic contact angle with distilled water. The results showed that thermal compression decreased the surface wettability of both loose and tight sides of the samples, especially for veneer samples compressed at a temperature of 180 °C. Tight side of the samples had lower wettability than loose side, even after thermal compression. Therefore, adhesive or any kind of finishing can be applied to both sides of thermally compressed veneer sheets without having any adverse influence on not only the bonding quality but also the whole finishing process.