Effect of pressing parameters on the shear strength of beech specimens bonded with low solvent liquefied wood

Abstract

Liquefied wood (LW) is a naturally based product which has the potential to be used as an adhesive. It can be used as a part of a polymer formulation, as a part of an adhesive mixture with commercial adhesives, or as an independent material for wood bonding. In this study, wood was liquefied at 180 °C using ethylene glycol as the solvent and sulphuric acid as a catalyst. In the first part of research, LW with different pH values was used for the bonding of solid wood at 200 °C for 15 min. In the second part, LW with an optimal pH value was used for bonding at different press temperatures for 15 min. In the third part, the minimum pressing time at the optimal pH value and at the optimal press temperature was determined. Unmodified LW with a negative pH value, a press temperature of 180 °C, and a pressing time of 12 min was determined to be optimal (based on highest shear strength) for the bonding of 5 mm thick wood lamellas with the LW used in this study. At these conditions bonds exhibited shear strength of around 7 N/mm² which was too low to attain standard requirements. Despite this, high wood failure (100%) was observed as a consequence of low pH value and high press temperature which caused damage of the part of beech lamellas where LW was applied.

Keywords:

• adhesive
• bonding
• liquefied wood
• shear strength
• pH value
• press temperature
• pressing time

Acknowledgments

The authors gratefully acknowledge the financial support of the Slovenian Research Agency through Project J4-2177 and Research Program P4-0015.