Evaluation of color variability of sliced oak veneer in the process of its manufacture

Abstract

Sliced veneer has the highest value as a facing material, provided that the natural color of the wood is preserved. Therefore, the study of the color characteristics of sliced veneer is of considerable practical importance. The object of the study is sliced veneer from European oak wood (Quercus robur L.), since it is produced in significant quantities by Ukrainian enterprises. The experimental studies were carried out under the production conditions of the Euroshpon LLC, which specializes in the production of sliced veneer. The color properties of sliced veneer were studied using the CIELab chromatic system. During the experimental studies, the duration of the steaming process was 16 hours at a steam temperature of 115°C, and the boiling process was 36 hours at a water temperature of 98°C. The sliced veneer samples were taken at a depth of 5 cm, 10 cm, 15 cm from the surface of the specimens for atmospheric drying and kept at a temperature of 20 °C and relative humidity near 50% during 14 days (for chamber drying at a temperature of 135 °C - within 120 s). In order to determine the natural color of oak wood, a reference sample of sliced veneer was taken, obtained from wainscots that had not undergone hydrothermal treatment. The sample was taken based on its uniform texture and color and obtained from logs that had not undergone hydrothermal treatment. Also, this sample was not subject to kiln drying. During the heat treatment (steaming, boiling), the temperature distribution across the cross section of the sample is not uniform. Wood at a depth of 50 mm warms up faster and to higher temperatures than at depths of 100 and 150 mm. According to the results of the experimental studies, the сolor scale readings of the reference sample are as follows: L*=65.80; a*=6.59; b*=23.39. The brightness of sliced oak veneer made from steamed wainscots and dried in the atmospheric conditions is L*=63.57-65.52, while the brightness of the sample dried in a drying chamber is L*=62.79-65.09. The brightness of sliced oak veneer made from boiled logs and dried in the atmospheric conditions is L*=63.82-65.43, the brightness of the sample dried in a drying chamber is L*=63.55-64.88. The parameter a* for sliced veneer sample taken from steamed wainscots is a*=5.03-5.58, and for sliced veneer sample taken from boiled wainscots is a*=6.24-6.97. The parameter a* for sliced veneer taken from steamed wainscots is a*=5.03-5.58, and for sliced veneer sample taken from steamed wainscots, the parameter a*=6.24-6.9 The component b* for sliced veneer sample taken from steamed wainscots is b*=20.21-20.85, and for sliced veneer sample taken from steamed wainscots – b*=20.47-20.99. The obtained research results can be applied in production conditions for the purpose of adjusting hydrothermal treatment modes and other processes in the manufacture of sliced oak veneer. The technological operation of oak logs boiling in the production of sliced veneer is recommended to be used in the case when it is necessary to achieve a lighter and more uniform color of the veneer, taking into account a longer process of heat treatment. Steaming oak logs has some advantages when it is necessary to increase manufacturing productivity without taking into account the color characteristics of the veneer.

Keywords

• quercus robur l.
• sliced veneer
• wood color
• cielab
• steaming
• drying
• heat treatment