Improving wet web runnability and paper quality by an uncharged polysaccharide

The effects of xyloglucan addition on wet web strength, drying tension and end product quality of bleached birch kraft pulps were examined with laboratory trials. Specific xyloglucan dosages were applied onto wet fibre networks by spraying. Laboratory sheets were prepared of never-dried and once-dried birch pulps. Wet sheet strength and drying characteristics were analysed using diverse analytical instruments. Structural, strength and surface properties of dry sheet samples were tested according to standard methods. Wet web strength and tension holding potential of test samples increased with the addition of xyloglucan, which is an indication of better wet web runnability. Xyloglucan also increased the drying tension. Besides enhanced runnability, xyloglucan treatment was also found to improve end product quality by improving smoothness and dry strength properties, and decreasing air permeability. Results indicate that xyloglucan treatment has greater strengthening potential with once-dried chemical pulp, whereas the effect with never-dried pulp was smaller. Never-dried fibre has high natural bonding ability when once-dried fibres re-swelling and thus bonding ability has deteriorated in drying process. Therefore, xyloglucan seems to have potential especially in recovering the strength properties of pulp with hornified cell walls, such as in recycled pulp. In general, these results can be exploited in paper and board machines for tailoring fibre networks for different product grades or special functional products.