Summary

The aim of this study was to investigate the surface composition and morphology of Chemithermomechanical pulp (CTMP) fibers from spruce. The fibers were exposed to a sequence of mild treatments such as washing, peroxide bleaching and extraction. The effects of treatments on fiber bulk composition and surface properties were investigated. All treatments did not significantly result in changes in total lignin and carbohydrate content. However, the extractives were stepwise removed. With the Electron Spectroscopy for Chemical Analysis (ESCA) technique, a gradual reduction of unoxidized carbon in the C1s resolved peak was shown, which was correlated to the removal of non-carbohydrates. Variations in surface topography among the analyzed samples were displayed with Atomic Force Microscopy (AFM) imaging of fibers in tapping mode. The wetting properties of all pulps were measured by Dynamic Contact Angle (DCA) on the single fibers. The advancing contact angle decreased and the hysteresis is also reduced, as a result of treatments. ESCA, AFM and contact angle analyses suggest that the extractives are distributed as globular particles at the fiber surface. Phase imaging AFM indicated the presence of lignin as irregular patches at the surface. A model of the CTMP fiber surface based on experimental findings in this work is proposed.