Process Factors Influencing Birch (Betula pendula Roth) Veneer Surface Properties and Bond Strength Development in Veneer-Based Products
This paper summarises the results of an ongoing study to determine the effect of process factors on the surface properties of birch (Betula pendula) veneer, focusing on bond formation with phenol formaldehyde resin. The impact of the hydrothermal pre-treatment of logs prior to veneer peeling and the drying of the veneers were studied and their effects upon surface properties were determined. Hydrothermal pre- treatment and drying were found to have an effect on the pH, wettability, colour, the depth of peeling checks in birch veneer and bond strength development in plywood. Increasing the hydrothermal pre-treatment temperature from 20℃ to 70℃, led to a decrease in surface pH values. The average water droplet contact angle on dry veneer surfaces that had been pre- treated at the higher temperature was found to be significantly lower than on dry veneers pre-treated at the lower temperature. The colour change of treated veneer surfaces was evaluated by the CIE L <*> a<*> b<*> system. The main results showed that not only drying conditions, but also the hydrothermal pre-treatment of the logs affected the colour of the veneers. At low temperature, yellowing occurred, which was observed in colour Coordinate b<*>, whilst notable differences in colour coordinates L<*> and a <*> were not detected. After drying the veneer colour became darker and less yellow. Bond strength was tested by two different methods. The first relatively widespread method is based on EN-314-1∶ 2005 and the second less prevalent method is the Automated Bonding Evaluation System. After low temperature pre-treatment of logs, the plywood shear strength was found to be lower than after high temperature hydrothermal pre-treatment. The difference between strength values with checks pulled open and when pulled closed is greater in the plywood pre-treated at the lower temperature and smaller in the higher temperature hydrothermal pre- treated group. The results were mainly affected by the depth difference in peeling checks, where the depth of peeling checks after hydrothermal pre-treatment at 20℃ were approximately 68％ and after pre-treatment at 60℃ were 49％ Similarly, the drying process was found to affect not only the veneer physiochemical properties, but also bond strength development.
Veneer surface properties wettability bond quality ABES
Anti Rohumaa Toni Antikainen Mark Hughes Martin Ohlmeyer
Laboratory of Wood Technology, Helsinki University of Technology, Tekniikantie 3, 02150 Espoo, Finla Federal Research Centre for Forestry and Forest Products, Institute for Wood Physics and Mechanical
国际会议
The Third International Symposium on Veneer Processing and Products(第三届国际胶合板制造技术研讨会)
上海
英文
131-139
2007-10-23（万方平台首次上网日期，不代表论文的发表时间）