Effects of zinc borate on the properties of medium density fiberboard

Since wood composites are increasingly used under conditions conducive to biodeterioration, more attention should be paid to their preservative treatment. We examined the resistance of medium density fiberboards treated with zinc borate to fungal and termite attack. Medium density fiberboards (300 by 300 by 2.7 mm) made of radiata pine (Pinus radiata D. Don) were treated with zinc borate to target retentions of 0.25 ,050, 1.00, and 1.50 percent boric acid equivalent(BAE). Zinc borate was incorporated into the fiberboards by introducing the chemical into the blender. Standard laboratory tests (JIS A 5905) demonstrated that there was no significant loss in mechanical or physical properties (modulus of rupture, modulus of elasticity, internal bond, water absorption, and thickness swelling) of the boards. A laboratory decay test using a monoculture of Trametes versicolor (L.: Fr.) Pilat and Fomitopsis palustris (Berk. et Curt.)Gilbn. & Ryv. showed that treated boards were well protected from both fungi at 1.00 percent BAE with a mean mass toss of less than 3 percent, whereas values of 4.7 and 28.0 percent were recorded with untreated boards, respectively, with T. versicolor and F. palustris after the same exposure period (8 wk.). Below 0.50 percent BAE the treated board specimens were attacked by subterranean termites (Coptotermes formosanus Shiraki) to some extent (40% of the untreated boards), and an increase in the zinc borate content (1.00 and 1.50% BAE)gave good termite protection in the laboratory. Field trials should be planned to determine the performance of zinc-borate-treated medium density fiberboards under conditions simulating practical applications.