Influence of knots on the adhesion of wood from young Eucalyptus grandis plantations

ABSTRACT

The structural use of wood from young trees requires gluing smaller timber pieces to form large elements. In young Eucalyptus timber of structural dimensions, knots do not significantly diminish the mechanical properties, yet their influence on wood adhesion has not been widely studied. Therefore, the aim of the study was to assess the influence of knots on the bond quality of face-glued wood from young E. grandis. Wood from seven-year-old E. grandis trees was tested in shear on the bond-line (polyurethane adhesive) using paired samples of knot-containing and clear wood samples. Knot features did not correlate with shear strength or wood failure percentage. Knot-containing samples had a lower percentage of wood failure (5.8%), but the same shear strength as clear wood samples. Below a wood density of 650 kg m⁻³, clear and knot-containing wood behaved similarly, but above this value, knots influenced wood adhesion negatively. By simulating glulam beams with high-density wood on the outer lamellas, it was possible to show that shear stress on those bond-lines is lower than the minimum shear strength observed on dense knot samples. Hence, lower adhesion caused by knots on denser wood probably does not represent a significant problem for glued laminated products from young Eucalyptus grandis trees.

KEYWORDS:

• Juvenile wood
• polyurethane adhesive
• shear
• glulam beams

Acknowledgements

The authors would like to thank Dr. Gustavo Burin Ferreria and Dr. Rafaela Pereira Naves for their constructive suggestions regarding the modeling approach.

Disclosure statement

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

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This study was financed by the Coordination for the Improvement of Higher Education Personnel (CAPES), Brazil [Finance Code 001, grant numbers 88882.180152/2018-01 and 88887.466463/2019-00].