REMOVAL OF WATER FROM PULPS BY PRESSING .1. INTER-WALL AND INTRA-WALLWATER

Water removal from pads of wet pulp under pressure was investigated. W ater pressed from the pad was quantitatively separated into two fracti ons-that expressed from the porous structure of the cell wall, and tha t expressed from spaces between fibers. Water from both locations star ts to be expressed from the pad at low pressure. However, almost all o f the water between fibers (and in the lumen) is removed at pressures below 2 MPa, leaving the water in the fiber walls as the predominant f orm of moisture remaining at higher pressures. The water content of pu lp pads pressed to high pressure was correlated linearly with the fibe r-saturation point (FSP), the initial level of moisture in the swollen fibers. Thus FSP is a measure of pulp pressability.