Effects of high temperature and high pressure alkaline pretreatments for the production of high strength resin-impregnated compressed wood

The possibility of using high temperature and high pressure alkaline pretre atment to improve mechanical properties of resin-impregnated compressed woo d was investigated. Sliced veneer of Hoop pine (Araucaria cunninghamiii) wa s treated at 120-170 degreesC for four or eight hours in an aqueous solutio n of NaOH or an aqueous solution of NaOH+Na2S (sulphidity: 25%) of 20-40% a ctive alkali. The weight loss due to the treatment reached around 30%. The Klason lignin analysis and the thermal softening behaviour under water-swol len conditions indicated that the weight losses due to the alkaline treatme nt of this study are mainly attributable to the removal of hemicellulose. T he treated veneer was impregnated with 25-30% by weight of a low molecular weight phenolic formaldehyde resin, and was parallel-laminated (nine plies) and compressed at 160 degreesC, 80 MPa for one hour. No significant differ ence could be observed between NaOH-pretreated wood and untreated wood. On the other hand, the veneer specimens pretreated with NaOH+Na2S solution at 120 degreesC or 135 degreesC, which resulted in 20% weight loss, exhibited 20% higher Young' modulus and bending strength than untreated wood. However , veneer pretreated at higher temperatures, 150 or 170 degreesC, did not sh ow further improvements in mechanical properties despite of increased weigh t losses.