Press-Drying of Softwood Bleached Pulp

Press drying is a technique where the wet sheet is simultaneously pressed and dried with z-directional restraint. Since fibrous materials, especially those from high yield pulps, become more pliable with press drying, improved strength properties of the sheet can be expected.Bleached softwood kraft pulpsheet was press-dried in this study to evaluate the potential applicability of this method to the effective use of wood resources.The results of the mechanical tests indicated that press drying was effective for bleached chemical pulpsheet as well as for high yield pulpsheet. This leads to the assumption that some mechanism other than lignin flow contributes to the superiority of mechanical properties of the press dried sheet. It is possible that the fibers become soft and compressible in the presence of heat and water even after lignin is removed from them. According to Scallan's model on the microstructure of pulp, shear deformation at an interfibrillar region takes place easily by external load when water penetrates the interlamella of the fibers.A denser part at both sheet surfaces was assumed by the results of the bending test. However, more careful experiments focussing on the sheet structure are required to draw a clear conclusion on a z-directional uneven mass distribution.