The Mechanisms Behind the Improved Dimensional Stability of Particleboards Made from Steam-Pretreated Particles

Summary

The mechanisms which cause an improvement in the dimensional stability of particleboards made from steam pretreated particles were investigated from the aspects of potential thickness recoveries of densified wood particles and the breakage of the adhesive bond network in particleboards. Since the latter would depend on the balance between bond strengths and stresses imposed on the adhesive bond, the effects of steaming temperature (160 to 220°C) on bond quality, recovery stress of compressed wood and in-plane swelling stress were investigated. Steam pretreatment was found: 1) to reduce thickness recoveries of densified wood particles, steaming temperatures above 190°C are especially effective, 2) not to cause a significant reduction in bond strength when steaming below 210°C or if relatively high press pressures of 1.5MPa are employed, 3) to reduce recovery stress of compressed wood, which is mainly caused by the increase in wood compressibility, 4) to reduce in-plane swelling stress of particles, which was found to correlate with reductions in both hygroscopicity and elasticity.