2007 Research Highlights

Research Area:
Strategic Goal: 1
SPA: Fire

Chemically modified wood to understand bond durability and adhesion.

Key Contact: Rebecca Ibach, ribach@fs.fed.us
within FPL RWU 4707 – Hunt, Brandon, Frihart

Determining adhesive bond performance for chemically modified wood is important not only in relation to its commercial utility but also because this information helps in understanding wood bond durability. Although wood modification is usually used to improve anti-swell efficiency, the modification can alter adhesive bond performance. Generally, modification is expected to diminish adhesion by making the wood surface less polar and less porous, resulting in poorer adhesive wetting of the wood and fewer chemical bonds between the two surfaces. On the other hand, chemical modification can help the wood bonds to pass water exposure durability tests because modified wood will swell less. Given the great variety of wood adhesives, species, and modification methods, a simple theory does not explain bonding behavior. A model was developed that takes into account the mechanism for dissipating stress induced by moisture-driven dimensional change, as well as general adhesion theories and adhesive–wood interactions, is useful for explaining our observations. The model is evaluated in relation to bond strengths and percentage wood failure for dry and water-soaked compressive shear blocks of yellow poplar sapwood. The wood was modified with acetic anhydride, butylene oxide, or propylene oxide to provide different polar characteristics for the wood and then bonded with adhesives that belong to both of the main groups in our model, the flexible and the reinforcing adhesives. Thus, the validity of this model for explaining the experimental results was evaluated. This knowledge should lead to a more systematic design of improved adhesives for bonding wood.