Abstract
Masson pine (Pinus massoniana Lamb.) samples were heat-treated at different treatment temperatures (150, 170, and 190 °C), and the nano-mechanical properties of the wood cell wall, which was coated with a waterborne polyacrylic (WPA) lacquer product, were compared. The elastic modulus (Er) and hardness (H) of wood cell wall and the coating were measured and characterized by nanoindentation, and the influencing factors of mechanical properties during thermal modification were investigated by chemical composition analysis, contact angle analysis, and colorimetric analysis. The results showed that with the increase in the heat treatment temperature, the contact angle of the water on the wood’s surface and the colorimetric difference increased, while the content of the cellulose and hemicelluloses decreased. After thermal modification of 190 °C, the Er and H of the wood cell wall increased by 13.9% and 17.6%, respectively, and the Er and H of the WPA coating applied to the wood decreased by 12.1% and 22.2%. The Er and H of the interface between the coating and wood were lower than those near the coating’s surface. The Er and H of the cell wall at the interface between the coating and wood were lower than those far away from the coating. This study was of great significance for understanding the binding mechanism between coating and wood cell walls and improving the finishing technology of the wood materials after thermal modification.
Highlights
Due to the fact of long-term exposure to external influences, such as water, heat, ultraviolet radiation, or mechanical stress, the properties of wood degrade [1,2]
Gurleyen et al [28] and Ayata et al [29] studied the effect of thermal modification on oak wood with different coatings, and the results showed that the lightness, adhesion strength, and hardness decreased with the intensity of the treatment
The hemicellulose of wood decreased after thermal modification, while the content of lignin increased with the increase in the temperature
Summary
Due to the fact of long-term exposure to external influences, such as water, heat, ultraviolet radiation, or mechanical stress, the properties of wood degrade [1,2]. The reduction of water adsorption is the key factor to improving the durability of wood products [8]. Cellulose and hemicelluloses contain large amounts of hydroxyl, which makes wood hydrophilic [9]. The extraction of cellulose and hemicelluloses can improve the properties of water-resistance wood [9,10]. Thermal modification refers to the heat treatment of wood in steam, air, inert gas, water, or oil, that is, through thermal decomposition of the internal physical and chemical compositions, the growth stress and drying stress of wood can Forests 2020, 11, 1247; doi:10.3390/f11121247 www.mdpi.com/journal/forests
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