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
Compatibility of nonacidic waterborne preservatives with phenol-formaldehyde adhesive
Thirteen nonacidic waterborne preservatives were in­ vestigated for their compatibilitywith phenol-formaldehyde adhesive on aspen veneer treated with the preservatives to retentions of 0.2, 0.4, and 0.6 pcf. Of these preserva­ tives, didecyl dimethyl ammonium chloride (DDAC), DDAC with copper, DDAC with carbamate (DDACCA),sodium fluoride,and ammonium hydrogen difluoridedid not inter­ fere with adhesion at any retention level. Carbamate in the DDACCA preservative apparently reinforced inter­ facial regions of the bondline to produce bond strengths much higher than those of untreated controls, particularly at the higher retentions. Ammoniacal copper zinc arsen­ ate at 0.2 pcf retention did not interfere with adhesion, but at higher retention levels bond integrity was below standards. All three borated preservatives that were stu­ died caused poor bonding, even at the lowest retentions. Emulsions of copper naphthenate, copper octoate, and zinc naphthenate also caused poor bonding. Determination of wet wood failure after vacuum-pressure soaking was more effective in detecting adhesion incompatibility than de­ termination of dry shear strength and wood failure after multiple cycles of vacuum-pressure soaking and drying.