Effects of surface characteristics of wood on bonding performance of low-molar ratio urea–formaldehyde resin

ABSTRACT

Low-molar ratio UF resin was used in bonding veneers of five wood species. Significantly different bonding strengths were observed among the used wood species. Much higher bonding strengths were found for cherry, sapele mahogany and black walnut, which would be attributed to their natural roughness that allows formation of more mechanical interlockings. After 60s Gliding Arc Discharge (GAD) plasma treatment of wood surface, the wet bonding performance was significantly improved for most of the wood species. The SEM images of wood surface indicated that the roughening, micrometer-scale peeling or etching effects of GAD plasma treatment would be related to the improved bonding performance. XPS characterizations showed that plasma treatment resulted in remarkable increase of O/C ratio for all wood species. Detailed analysis of C1s spectra revealed that drastic oxidation induced by plasma generated high content of oxygen-containing groups, while degradation led to exposure of more oxygen-containing components like cellulose and hemicellulose. In contrast to untreated surface, stronger interactions can be formed between highly polar wood surface and UF resin. GAD plasma appeared to be an efficient tool in both physical and chemical modifications of wood surface.

KEYWORDS:

• surface characteristics of wood
• natural roughness
• plasma treatment
• urea–-formaldehyde resin
• bonding performance

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Key Program of Applied and Basic Research in Yunnan Province (Grant No. 202101AS070008) and the Open Foundation of the Key Laboratory of State Forestry and Grassland Administration on Highly-Efficient Utilization of Forestry Biomass Resources in Southwest China, Southwest Forestry University (No. 2021-KF-04)