Biological resistance of steam-compressed wood pretreated with boric compounds
M K Yalinkilic, W Dwianto, Y Imamura, K Tsunoda, M Takahashi
Wood compression under heating is aimed to enhance dimensional stability and surface hardness. Preservative treatment with an appropriate chemical is additionally required for the protection of wood against biological agents under hazardous service conditions. Boron pretreatment of compressed wood was targeted to a mutual benefit of increasing biological resistance of compressed wood as boron was converted to a more stable form through hydration and dehydration reactions under steaming at elevated temperatures in a closed system. Accordingly, boric acid (BA) (at 0.25, 1.00 and 4.70% aqueous concentration)- or phenylboronic acid (PBA) (at 0.34, 0.50, 1.00 and 2.00% aqueous concentration)-impregnated Japanese cedar (Cryptomeria japonica D. Don) specimens were compressed at their radial direction to 50% dry set at 171, 180 and 200°C. The compressed specimens were subjected to decay and termite tests following exposure to a severe ten-cycle wet/dry processes according to Japanese Industrial Standard JIS K 1571 (1998). BA pretreated-compressed wood exhibited remarkable resistance against a white-rot fungus, Trametes versicolor, but not so effective against a brown-rot test fungus, Fomitopsis palustris even at high boron loads which resulted in a high termite resistance. PBA pretreatment appeared to be very effective against both decay fungi and Formosan subterranean termite when wood specimens were compressed at high temperatures and steam pressure.