Interaction between cellulose and xylan: An atomic force microscope and quartz crystal microbalance study

The atomic force microscope (AFM) colloidal probe technique has been used to investigate forces between cellulose beads as well as cellulose beads and mica in aqueous solution, and the interaction between cellulose surfaces in xylan solutions. Several observations of the behaviour of the cellulose beads were made. Swelling of the beads in aqueous solutions is rather slow. Thus, it is important to let the beads equilibrate before measurements. The beads are somewhat compressed when forced together to constant compliance, but relax back to their original shape in a few minutes. A long-range electrostatic repulsion between cellulose and mica occurs on approach. The xylan concentration in solution affects the forces between two cellulose surfaces. When the concentration increases from 10-100 mg/I more xylan adsorbs slowly and irreversibly on the cellulose leading to an increasingly long-range and stronger repulsion between the surfaces on approach. Adhesion between the layers is very low and seems to be due to entanglement of polymer chains. Studies of the adsorption of xylan (100 mg/1) on cellulose films with a quartz crystal microbalance with dissipation (QCM-D) verify that a thick, water-swollen layer of xylan is formed by slow adsorption. It has been proposed that adsorbed xylan on fibre surfaces increases paper strength. We conclude that this must be associated with the behaviour of the adsorbed layers of xylan on drying.