The mechanisms behind the improved dimensional stability of particleboardsmade from steam-pretreated particles

The mechanisms which cause an improvement in the dimensional stability of p articleboards made from steam pretreated particles were investigated from t he aspects of potential thickness recoveries of densified wood particles an d the breakage of the adhesive bond network in particleboards. Since the la tter would depend on the balance between bond strengths and stresses impose d on the adhesive bond, the effects of steaming temperature (160 to 220 deg rees C) on bond quality, recovery stress of compressed wood and in-plane sw elling stress were investigated. Steam pretreatment was found: 1) to reduce thickness recoveries of densified wood particles, steaming temperatures ab ove 190 degrees C are especially effective, 2) not to cause a significant r eduction in bond strength when steaming below 210 degrees C or if relativel y high press pressures of 1.5 MPa are employed, 3) to reduce recovery stres s of compressed wood, which is mainly caused by the increase in wood compre ssibility, 4) to reduce in-plane swelling stress of particles, which was fo und to correlate with reductions in both hygroscopicity and elasticity.