Detecting Wood Extractives on Pulp Fibre Surfaces Using AFM and ESCA

The morphology of wood resin precipitated on bleached kraft pulp surfaces has been investigated using AFM and ESCA techniques. We show how an alternative approach, i.e. elemental depth distributions derived from spectral background can be used in combination with the surface concentrations data to facilitate the interpretation of AFM data in geometrically complex systems. Extractives, leached from thermomechanical pulp using hexane, were dissolved in acetone and then precipitated in water. Different amounts of extractives dispersion was thereafter applied on pulp surfaces. AFM phase images suggested that the precipitated extractives formed a thin film on the fibre surface. Conventional ESCA analyses verified the presence of extractives on the pulp surfaces. Furthermore, the changing peak-to-background ratio of the oxygen signal in the measured ESCA spectra indicated that the depth distribution of oxygen was changing with the addition of the dispersed extractives. The background data supported the hypothesis that the extractives were adsorbed as a thin film covering the pulp substrate. The results were also compared to AFM images of deposited resin on other surfaces.