Novel bulking technologies for cellulose fibres

This paper deals with the details of preparation of three principal routes for bulking of cellulose fibres. One route is dry cross-linking/hornification using aluminium ions and other salts followed by drying/curing. The mechanisms of these reactions still remain unknown. A second route is physical grafting of fibres using carboxymethylcellulose and bringing the acidic groups into their aluminium form before forming a sheet of paper/board. Hence, curing is not necessary, and this constitutes a unique wet bulking methodology. The mechanism behind this method is believed to be an increase in the surface friction of fibres, when the electrostatic double layer is shielded together with electrostatic cross-linking with aluminium ions. The higher friction between fibres partly prevents the sheet consolidation during drying. A third route is physical grafting of fibres using carboxymethyl cellulose and ion-exchanging the acidic groups with aluminium salts before drying and curing of the fibres. A most interesting factor is that all the thermal treatment methods do not form fibre nodules due to interfibre crosslinking during the heat treatment, a commonly observed phenomena when dealing with chemical crosslinking of fibres. All routes investigated are water-based and should be fairly simple to implement in commercial operations. An inherent advantage is that the bulking is associated with lower water retention values, which should be advantageous for a higher solids content after pressing and, hence, beneficial for paper machine productivity. Bulking is, however, also associated with a loss in bond strength, which in most cases must be alleviated using various additives such as starches and microfibrillated cellulose and it has also been demonstrated in the project how the strength properties (such as z-strength) could be restored at a higher bulk.