Comparison of the effect of chemical and mechanical treatment of end-grain surfaces on adhesive bond strength

Abstract

End-grain surfaces of spruce wood specimens that were planed with a microtome knife were chemically modified by treatment with bleaching reagents, namely sodium hypochlorite and peracetic acid, and the effect of the surface modification on bond strength of end-grain joints was studied. The chemically treated samples were compared with sawn surfaces, microtome-planed specimens that were additionally irradiated by light, and surfaces that were solely planed with a microtome knife. Significantly higher bond strength compared with the microtome-planed specimens was observed for the sawn specimens and for hypochlorite-modified samples. These findings were ascribed on the one hand to an increased surface roughness resulting from the mechanical process of sawing leading to an enlargement of the bonding area. On the other hand, during the etching process with sodium hypochlorite a pulp of cell walls and cell wall fragments was formed, leading to a partially closed surface which prevented overpenetration of adhesive into the opened cells.

Keywords:

• Adhesion
• bonding
• end grain
• surface treatment
• tensile strength

Acknowledgements

The authors gratefully acknowledge the financial support by the Berger Solution Group and the Competence Centre for Wood Composites and Wood Chemistry, Wood K plus. Many thanks go to Dr G. Zuckerstätter, Wood K plus, Lenzing, Austria, for his help with scanning electron microscopy, and I. Taudes W3C, St Veit an der Glan, Austria, for her help with the optical 3D Infinite Focus® metrology.