Effect of wood microstructure and hygroscopicity on the drying characteristics of waterborne wood coating

• Published in: Wood science and technology 2022-05, Vol.56 (3), p.743-758
• Main Authors: Song, Xiaoxue, Han, Guangping, Jiang, Kaiwen, Chi, Xiang, Liu, Dajun, Zhang, Hanxi, Cheng, Wanli, Shi, Sheldon Q.
• Format: Article
• Language: English
• Subjects: Air drying; Balsa; Biomedical and Life Sciences; Ceramics; Coating; Coatings; Composites; Contact angle; Drying; Efficiency; Evaporation; Furniture; Glass; Humidity; Hygroscopicity; Influence; Investigations; Life Sciences; Machines; Manufacturing; Moisture effects; Moisture gradient; Natural Materials; Oak; Original; Polyurethane; Polyurethane resins; Processes; Radar maps; Relative humidity; Substrates; VOCs; Volatile organic compounds; Water absorption; Water transfer; Wood; Wood Science & Technology; Wood sciences
• ISSN: 0043-7719; 1432-5225
• DOI: 10.1007/s00226-022-01377-y

The drying process of waterborne wood coating (WWC) is mainly driven by the moisture gradient, part of the water evaporates to the air, other part enters into the wood structure. The water absorption and conduction rate vary within various wood substrates, which have a great influence on the drying rate of WWC. Herein, the focus of this paper is on studying the influence of water movement behavior on the drying efficiency and film-forming performance of WWC under conventional hot-air drying process. A waterborne acrylic-polyurethane was used as representative coating in the study. It was found that balsa wood had more pores and higher specific surface area than oak wood, allowing a faster water transfer at the wood surface. The shortest surface and hard drying time of 573 s and 1393 s were achieved at 60 °C and 40% relative humidity for WWC on balsa wood. The dynamic drying rate study showed that the water transfer on the surface of oak was slower than that of balsa. Based on the film-forming performance of WWC under different drying conditions, a better film property could be obtained by adjusting the drying conditions to achieve a dynamic balance between water evaporation to air and water transfer into the wood substrate. The drying characteristics of WWC on different wood surfaces and drying conditions were comprehensively evaluated by radar map analysis. The results in this work contributed to the efficient and green processing in furniture and coating industries.