Accumulation of specific dissolved and colloidal substances during white water recycling affects paper properties

The compositions of white water from a newsprint machine and model recycled white waters (1-5 times) were determined. The effects of these white water s on paper properties were compared and related to differences in their com position. It was found that the level of total dissolved and colloidal subs tances and the concentration of each group of the components within the whi le water increased sequentially after each recycle step. The dissolved and colloidal substances were primarily composed of carbohydrates, lipophilic e xtractives and lignins. A highly recycled white water and a regular mill wh ite water were used to make handsheets. The strength, optical, surface and wet web properties of the handsheets were significantly impaired when white water was used in place of distilled water during handsheet preparation. L ipophilic extractives reduced interfibre bonding and sheer consolidation re sulting in a decrease in handsheet density of around 10%, a decrease in ten sile strength of 20-30% and, at lower concentrations of dissolved and collo idal substances, increased porosity and rates of water absorption. These ef fects were partially offset by increasing levels of colloidal material whic h resulted in significant reductions in porosity and snte of water water ab sorption. Higher concentrations of lignin-derived material increased light absorption of the handsheets with corresponding brightness decreases of up to 10 points ISO. The presence of resin and fatty acids in the white water decreased water surface tension with a concurrent decrease in wet-web stren gth and papermachine runnability.