Dissolved and colloidal substances accumulating in papermaking process waters

Disturbances in the wet end can affect both the paper machine runnability and the paper quality. If things go wrong in the wet end, little can be done later in the papermaking process to remedy the problems. Wet end disturbances are often directly related to the different dissolved and colloidal substances (DisCo's) accumulating in the wet end. The DisCo's are coming into the wet end primarily with the pulps, and are mainly wood-derived components released from the fibers or residual pulping chemicals. Mechanical pulps carry over much more DisCo's than chemical pulps and recycled pulps. The paper reviews important findings on the chemical character and interactions in the wet end of hemicelluloses, pectins and wood resin (pitch) with focus on production of wood-containing paper grades. It is concluded that it is necessary to go deeper - beyond the coarse sum parameters - to the molecular level to achieve real understanding of wet end chemistry and the phenomena and mechanisms involved.