THICKNESS SWELLING AND INTERNAL BOND STRENGTH OF PARTICLEBOARDS MADE FROM STEAM-PRETREATED PARTICLES

Particleboards with a density of 0.5-0.8g/cm(3) were manufactured with semi-strand particles previously steam-treated at 180-210 degrees C w ith urea-formaldehyde resin. The effects of the steam temperature and panel density on panel thickness swelling (TS) and internal bond stren gth (IB) were investigated. The reductions in TS and spring back were found to be greater at higher steam temperatures; there was a trend fo r the effect of reducing TS to be slightly greater at larger panel den sities. Although the steam pretreatment reduced the panel IB by up to one-fifth, it provided the panels with less reduction of IB when they were subjected to a wetting/drying cycle. This suggests that steam pre treatment plays a role in reducing the breakage of the adhesive bonds between particles. Furthermore, the effects of the steam pretreatment on bond quality were investigated by a delamination test of veneers, A lthough the bond strength decreased with increasing steam temperature when smaller press pressures were applied, there was no noticeable dif ference of bond strength between treated and untreated veneers when pr essed at 1.47 MPa.