Specific ion effects in carboxymethyl cellulose adsorption on cellulose: A step towards modification of fibers in fiber line
Sammanfattning: The increasing global demands for paper products have fuelled the research in developing new fibers from existing industrial processes. The adsorption of carboxymethyl cellulose (CMC) has been shown to improve the tensile properties of the paper significantly. One way to manufacture such modified fibers is to integrate the CMC adsorption step in current pulping mills. However, the mechanism behind the adsorption of CMC on cellulose surfaces is still not fully understood, even if the literature on this subject is extensive. This thesis discusses the controlling factors and mechanism behind the adsorption of CMC on cellulose surfaces, which can enable future integration of adsorption process within the pulping mill. The adsorption studies have been carried out mainly on model cellulose surfaces using QCM-D and it was shown that the CMC absorption depends on the amount and type of added cations and anions. The ion specificity in CMC adsorption was explained by these ions' ability to induce dispersion forces and hydration regulated positioning of ions at the interface. The observation that CMC adsorption on the model system is ion-specific was confirmed in a study where CMC was absorbed on commercially available softwood kraft pulp. Furthermore, CMC adsorption on cellulose model surfaces in the presence of D2O or H2O revealed that this process is entropy driven, which was supported by temperature dependent adsorption experiments.
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