Anionic groups in fibre surfaces as investigated by XPS, FTIR-ATR and different sorption methods

摘要

Charged or anionic groups (AGs) are the most important functional groups in pulps because they can remarkably influence fibre swelling, refining, strength properties and interactions with paper chemicals. AGs groups are usually classified as bulk and surface AGs, according to the method used for determination. Total or bulk AGs can be determined by different titration and sorption techniques, while estimation of surface AGs is still based on one method, the polyelectrolyte adsorption technique. In this work, we present a new alternative for determination of surface AGs using methylene blue sorption and X-ray photoelectron spectroscopy (XPS). We compare the results obtained with the polyelectrolyte (PE) titration and evaluate the different shapes of MB and PE isotherms in kraft and CTMP pulps using a combination of XPS and FTIR-ATR measurements. We show that MB and PE sorption are reversible processes. We also show that the content of AGs on fibre surfaces estimated by MB and XPS is much lower than those obtained using polyelectrolyte sorption. The implications of competition between different cationic chemicals for surface AGs in papermaking interactions and paper properties are also discussed.