Abstract
Semi-strand (22.8mm×2.6mm×0.5mm) particles were prepared from small-diameter sugi (Cryptomeria japonica) logs obtained by thinning operations. The particles were treated with saturated steam for various preselected times. The saturated steam pressures used were 3.6, 6.2, 10.5, and 16.5kgf/cm2. The treated and untreated particles were then used to produce boards using urea-melamine formaldehyde resin as a binder. On the other hand, the chemical change of wood after steam pretreatment was investigated. The amount of water solubles and alcohol-benzene extractives increased with increasing treatment time and steam pressure. The pH of the treated wood decreased from 5.80 to 3.91. When the relative humidity was increased from 65% to 96%, the thickness swelling of the boards was reduced drastically by a high temperature steam pretreatment for a short period of time. The control board showed a linear expansion of 0.37% compared with a linear expansion of 0.25% for the boards made of the particles steam-treated 16.5kgf/cm2 for 1 minute. The modulus of elasticity of the boards increased with steam treatment time. Modulus of rupture and internal bond strength was affected adversely by the steam treatment.
