HETEROGENEOUS FIBRILLATION OF KRAFT PULP FIBER SURFACES OBSERVED BY ATOMIC-FORCE MICROSCOPY

Atomic force microscopy (AFM) has been used to image local surface var iations and to measure force-distance curves for bleached softwood kra ft pulp fibres in air and in aqueous media. The interactions between t he AFM silicon nitride tip and the fibre surfaces depend strongly upon the microfibrillation of the sample surface introduced by mechanical treatment. The degree of fibrillation varied from place to place on a given fibre surface. In a low-fibrillation area, a clear surface image was observed and there were no long-range interactions as the AFM tip approached the surface. However in a high-fibrillation area, local im aging became veiled and a significant repulsive interaction,vas observ ed at large tip-sample separations (up to 2 mu m) due to the presence of microfibrils extending out from the surface. This long-range repuls ion decayed with increasing salt concentration The results are interpr eted in terms of fibril-fibril and fibril-surface electrosteric intera ctions.