Interactions of calcium(II), copper(II) and aluminium(III) ions with two chemically modified wood fibres
2001 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 16, no 3, 225-34 p.Article in journal (Refereed) Published
Two chemically modified softwood fibres, carboxymethylated cellulose (CMC) and 2,3-dicarboxylic cellulose (DCC), have been characterised with respect to acid/base properties and metal ion affinity. The experiments were performed as series of potentiometric titrations at 25 degreesC and at constant ionic strengths of 50 and 100 mM Na(Cl). Data showed that the amount of acidity in each pulp was independent of the ionic strength employed.
In modelling the acid/base properties of both pulps, equilibrium models comprising two intrinsic dissociation constants and a co-optimised specific capacitance value were found capable of explaining all data collected at -log[H+]less than or equal to6. However, the acidity of the functional groups on the fibres increased, and the influence from electrostatic effects decreased, with increasing ionic strength. The metal ion affinity studies involved the ions Ca2+, Cu2+ and Al3+. Complementary information concerning metal ion-fibre interactions at the molecular level was obtained from IR measurements. It was found that the simple Donnan equilibrium model was inadequate for modelling these interactions and it was concluded that specific metal ion-fibre interactions occurred. For an equilibrium reaction in which two fibre sites interact with one metal ion, an equilibrium model was found that could explain all data in the examined -log[H+] and metal ion concentration ranges, for both pulps, and for all three metal ions examined. In the aluminium(III)-DCC system, also a tendency to hydrolysis of the Al-fibre complex was indicated. The two pulps had significantly different acid/base- and metal ion affinity properties, which mirrors significant differences in the local chemical environment of the carboxylic groups in the two pulps. The IR measurements indicated no direct interactions between the Ca2+ and Cu2+ ions and these carboxylic groups, implying that the complexes formed have a predominant outer-sphere character. In contrast, IR data clearly showed an inner-sphere coordination between Al3+ and the carboxylic groups on the fibres.
Place, publisher, year, edition, pages
2001. Vol. 16, no 3, 225-34 p.
chemically modified softwood fibres, acid/base properties, ionic strength, metal ion complexation, potentiometric titrations, IR measurements
IdentifiersURN: urn:nbn:se:umu:diva-8999DOI: doi:10.3183/NPPRJ-2001-16-03-p225-234OAI: oai:DiVA.org:umu-8999DiVA: diva2:148670