Surface polarity determination of wood fibres after different pre-treatments and bisulphite pulping
THE SURFACE POLARITY OF PULP FIBRES originating from four different wood species commonly used for pulping in South Africa has been determined after various pre-treatments, and after magnesium bisulphite pulping. The presence as well as the distribution of polar groups on the fibre surface strongly affects inter-fibre bonding in paper. Bonding consists mostly of hydrogen bonds between free hydroxyl groups on the fibre surface. Surface polarity was examined by atomic force microscopy in pulsed-force mode. This technique allows the imaging of the polarity of a surface with a nanometre-scale molecular resolution. It is thus sensitive to individual functional groups, mostly hydrophilic hydroxyl groups. Polarity differences between the various wood species have been observed. We compare these observations with the varying pulp quality that arises from the pulp composition. Improvement in pulp quality may be possible if fibre surface properties are used as guidance criteria for the choice of a specific pre-treatment method.