Enhancement of Biological and Physical Properties of Wood by Boric Acid-Vinyl Monomer Combination Treatment

Abstract

Boron treatment was combined with vinyl polymerization to improve leaching resistance of boron from wood, as well as dimensional stability, biological and fire resistance of wood. Boric acid (BA) was impregnated into wood specimens [sapwood of Cryptomeria japonica D. Don. 20 (T) x 20 (R) x 10 (L)mm] as 1% aqueous solution prior to vinyl monomer treatment. Styrene (ST), methylmetacrylate (MMA) and their mixtures (50:50, v/v) were impregnated in the presence of catalyzer and a crosslinker. Polymerization was conducted by heat radiation method at 90°C for 4h. Treated specimens were then subjected to decay and termite tests, as well as oxygen index (O.I) determination. Anti-swelling efficiency (ASE) and water absorption levels (WA) were also measured by standardized methods. Vinyl monomers succeeded in reducing WA of wood to a minimum level and delay boron leaching considerably. The treated wood proved to be resistant against two decay fungi, Tyromyces palustris and Coriolus versicolor and very destructive termite Coptotermes formosanus even after ten severe weathering cycles. BA increased the O.I. levels of monomer-treated wood, which resulted in a lower flame spread index. Moreover, BA suppressed the smoke generation due to monomer cooperation in wood.