Surface charge characterization of pulp fibers and charge distributions in papermaking slurry

This dissertation presents a novel technique for the determination of cellulose fiber surface charge. Unlike previously applied methods, the current approach is able to quantify the charge of single wood fibers. The blue emitting fluorescent stain N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE) was found to be a charge sensitive fluorophore for anionic cellulose fibers. The adsorption of MQAE onto charged cellulose fibers was quantified and found to follow the accepted theory of 1:1 ion exchange for low molecular weight adsorption onto cellulose fibers by electrostatic attraction. Quantification of surface charge by fluorescence requires a reference dye to eliminate confounding factors commonly encountered when relating fluorescence intensity to another property such as charge. The polymeric red emission of Acridine Orange (AO) was found to be an ideal charge-insensitive reference stain. Regardless of charge, the mean red (AO) intensity remains constant. The mean titration-determined charge values for multiple pulp samples were then correlated with their mean blue (MQAE) emission divided by mean red (AO) emission. A linear calibration was established between the accepted charge titration technique and the blue/red ratio for multiple pulp samples. A similar relationship was found between MQAE fluorescence emission and MQAE binding. With this relationship, it was possible to infer the charge of individual papermaking particles by their blue/red fluorescence ratio. Through the application of fluorescence staining, imaging flow cytometry, and multiple wavelength emission quantification and analysis, charge distributions of fibrous slurries were determined. The application of this technology will allow for greater understanding and control of complex wet-end electrochemical interactions.