ELSEVIER Applied Surface Science 75 (1994) 213-219 iiiii i i ii ii ii !iiiii !ii iii ii ii i iii iiiiii i ii iiii i ii i iii i applied surface science Studies of cellulose surfaces by titration and ESCA Per Stenius *, Janne Laine Laboratory of Forest Products Chemistry, Department of Forest Products Technology, Helsinki Unicersity of Technology, Vuorimiehentie I A, 02150 Espoo, Finland (Received 17 June 1993; accepted for publication 23 August 1993) Abstract The surface properties of unbleached kraft pulp fibers of varying lignin content prepared by digestion with different amounts of excess alkali have been investigated using polyelectrolyte titration, potentiometric titration and ESCA. The surfaces contain two different acidic groups that dissociate completely above pH 7.5, one with pK = 3.6 and one with pK = 5.7. The amount of the latter group correlates directly with the amount of lignin in the pulp. The ESCA analysis indicates that the relative amount of carboxylic groups and alkyl carbon in the surface decreases as the lignin content decreases and also that material with high alkyl carbon content is enriched in the outermost surface of the cellulose. Thus, a combination of ESCA analysis and high-precision titrations is able to yield a very detailed picture of the effect of digestion conditions on surface properties of cellulose fibers of direct relevance to paper properties. 1. Introduction Cellulose fibers are among the most important raw materials and bearers of information used by mankind. In spite of this, there is still very much to be learnt about the surface properties of these fibers. Thus, the understanding of how they affect properties such as paper strength, the spreading and adsorption of printing inks and the recyclabil- ity of fibers is still rather incomplete. In particu- lar, the use of new types of wood and the devel- opment of new digestion, bleaching and washing * Corresponding author. procedures in the manufacture of pulp has high- lighted the need for a better understanding of the physics and chemistry of cellulose surfaces. The new surface spectroscopies appear to offer inter- esting possibilities to obtain detailed chemical information. However, the complexity of the sur- face implies that a full characterization and un- derstanding of its properties can be obtained only by a combination of several methods of investiga- tion. In the following, results will be presented from a study of cellulose surfaces that aims at (i) developing methods to characterize the charge, surface energy and chemical composition of cellu- lose surfaces, (ii) applying these methods in stud- ies of fibers prepared by different methods of digestion, bleaching, washing and recycling. Our 0169-4332/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 01 69-4332(93)E0206-2