The benefits of using sodium borates as a wood preservative against a variety of insects and fungi have been long known. On the other hand, sodium borates are leachable and have an adverse effect on the mechanical properties of composite wood panels. In a previous study ( ), a pilot plant trial on sodium borate-treated OSB was carried out and commercial size panels were subjected to a numbers of tests, e.g., mechanical evaluation, fire, termites and decay resistance. In this study, efforts have been made to improve the mechanical properties and reduce leach out behavior of the borate-treated panels.
Ten series of experimental panels were prepared to evaluate the effect of zinc borates (BoragardRZB) on the properties of OSB panels. Polyethylene glycol was used as the flowing agent. In the first five series, treated panels were bonded with phenol formaldehyde (PF) novolac-type resin while resole PF was used in the second five series. The mechanical properties of panels, treated with zinc borate and bonded with resole PF, were found to comply to the CSA requirements. Panels made with novolac PF and treated with 1% and 2.5% borate met all the CSA requirements, except MOR after a two-hour boil test. It should be noted, however, that the 5% borate-treated panels had excellent results in MOR after the same boil test. Creep tests results showed no evidence that borates will have any adverse effect on the long term performance of treated panels. The results of leaching tests have suggested that BorogardRZB treated panels can be used in an unprotected environment without any significant reduction in protection. Decay tests have shown that treated panels were not subject to attack by Gloeophyllum trabeum or Coriolus versicolor. Weight losses for treated panels were under 1% and no fungal growth was observed. Resistance to Formosan termite attack is being conducted in field tests conducted in Hawaii. Complete test results are expected by 1997 at which time a supplementary report will be prepared.