The effect of acetylation on the shear strength development kinetics of phenolic resin-to-wood bonds.

摘要

Chemical pretreatment of materials used in wood-based composite products before lay-up and pressing has some advantages over the post-treatment of panels. However, pretreatment may affect the relationship between temperature and strength developmentrate of adhesive bonds (as well as final strengths). Such relationships affect minimum pressing times and the consequent economic viability of panel production. Acetylation is a possible chemical pretreatment. The effect of acetylation level on the strength development rates of small phenol-formaldehyde-to-wood test bonds was therefore investigated. Pieces of maple (Acer macrophyllum) measuring 0.8 X 20 X 106 mm were acetylated with acetic anhydride at 120deg C to achieve weight percentage gains of 8.17,11.62, and 14.49. Bonds were formed at pressing temperatures of 86, 97, 107, and 113deg C for a variety of times and were immediately thereafter tested in shear mode. An automated bond formation and evaluation system (ABES) was used for this purpose. Four near-isothermal bond strength development curves were constructed for each acetylation level. The curves suggest differences in shear strength development rates at the early stages of bond development. Linearly regressed early rates were affected by bothtemperature and acetylation level, although the effect of acetylation level was small. Cold and fully cured bond strengths were impaired by acetylation; this is consistent with others' findings.