Effects of Postlayup Borate Treatment on Appearance and Flexural Properties of Douglas-Fir Glued Laminated Beams
Abstract Preservative treatments are required whenever glued laminated beams are exposed outdoors. Treatments can be either water-based systems applied to individual laminations prior to layup or o...
Effect of Polyborate Pre-treatment on the Shear Strength Development of Phenolic Resin to Sitka Spruce Bonds
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
A Technique to Evaluate the Bonding Reactivity of Thermosetting Adhesives
The rate at which thermosetting adhesive bonds develop strength critically effects the economic viability of many manufacturing processes. Bonds between the constituents of laminated and particulate panel products, overlays, and moldings must, for example, attain a certain minimum strength before the hot press used in their manufacture may be opened. A technique is reported that will prove useful to adhesive technologists endeavoring to develop resins with reactivities tailored to the specific conditions occurring within products during their manufacture. With the technique, many small lap-shear bonds pressed under controlled conditions of temperature and load are pulled after a range of curing times for measurement of their accumulated shear strength. This enables a family of shear-strength development curves to be constructed for a range of nearly constant temperature conditions. The effect of temperature on the bonding kinetics of the adhesive-adherend combination may thereby be evaluated. The technique lends itself to standardization for use in commercial laboratories, requiring much simpler sample preparation and apparatus than previously reported methods in which bonds are tested in tension perpendicular to the glueline. Wood adherends and a liquid phenol formaldehyde adhesive are used in a candidate system demonstrating the technique.