Fast determination of anionic groups in different pulp fibers by methylene blue sorption.

Application: Anionic groups in pulps can be determined for process control in pulp and paper mills using "at-line" or "on-line" conditions.

Methylene blue (MB) sorption can be used for determination of anionic groups (AGs) in chemical, chemimechanical, and mechanical pulps. Fast sorption performed in 5 min under vigorous agitation gave similar results as obtained using 20 h sorption time, with no observed effects of AG counter ions. The MB sorption isotherm showed different plateaus according to the amount of free MB in solution. We also identified regions related to chemisorption and physisorption. For analytical purposes, the saturation level in the chemisorption process must be the target for performing MB sorption. The isotherm in the chemisorption region for this study was of the Langmuir type, according to experimental data fitting and as observed by X-ray photoelectron spectroscopy (XPS) analyses. Through this study, we show the potential application of MB sorption for "on-line" and "at-line" process control in pulp and paper mills as a fast and reliable method.

Fardim and Holmbom are with Abo Akademi University, Process Chemistry Group, Porthansgatan 3, FIN-20500, Turku/Abo, Finland. Email Fardim at [e-mail], Holmbom at [e-mail].