Abstract
Pre-treating the constituents of wood-based composite panels with fungitoxic chemicals prior to lay-up and pressing offers some advantage over post-pressing treatment. Boron is a strong candidate pretreatment chemical for this application but it influences the bonding mechanisms that must occur during hot pressing. In the present study, the effects of boron loading level (A to 15% boric acid equivalent, BAE) on the strength development rates of small phenol formaldehyde-to-wood (sitka spruce) test bonds was investigated. Each bond (15 mm x 15 mm overlap) was formed under pre-selected time (20 to 240s) and temperature (70, 80 or 95 °C) conditions and immediately thereafter tested in shear mode, this enabled three approximately isothermal bond strength development curves to be constructed for each boron loading level investigated. All levels of boron pretreatment hastened initial strength development rates, although levels above 7.5% BAE had diminishing effects on isothermal rates - with possible decreases at very high (15% BAE) levels. Though not exactly reproducing conditions that occur around bonding sites in panels during pressing, the techniques described may aid in our basic Understanding of the mechanisms affected by chemical pretreatment. © Copyright 1993 by Walter de Gruyter
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