Improving the dewatering properties of never-dried chemical pulp by pressing before refining

Refining of never-dried chemical pulp increases fiber swelling that deteriorate its dewatering properties in the papermaking process, in particular in the press section. Drying before refining can improve the dewatering properties but is costly for integrated pulp/paper mills. In the present work, an attempt was made to find a more economical way to improve the dewatering of chemical pulp, while maintaining its strength properties. Never-dried softwood kraft pulps were pressed before refining. Results showed that the pressing hornified (reduces the swelling of) the pulp fibers and thus improved the dewatering. The pressing also improved the sheet density and tensile strength but decreased the light scattering coefficient. It was explained that the pressing not only caused hornification but also flattened fibers and provides more surface contact for bonding. When pressed to a higher solid-content of about 66%, the pulp had almost the same tensile strength as the untreated pulp but with improved dewatering properties.