Concentration effect of TEMPO-oxidized nanofibrillated cellulose aqueous suspensions on the flow instabilities and small-angle X-ray scattering structural characterization
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The rheological behavior of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized nanofibrillated cellulose (NFC) suspensions at different concentrations were examined using Couette with smooth and serrated surfaces and vane-in-cup geometries. A slippage against the walls of rheometer rotor or/and stator (wall-slip) as well as flow localization within a specific volume of the sample (shear banding) took place. These phenomena were visualized using a technique based on introduction of titanium dioxide pigment into the specific volume of NFC suspension and monitoring its deformation. The flow instabilities appeared more pronounced with an increase of the NFC concentration. It was shown that the use of serrated geometry is necessary to compete with the wall-slip but is not sufficient to prevent it completely. Serrated Couette was found to be the most appropriate geometry (among the tested) to measure the rheological properties of NFC suspensions. Small-angle X-ray scattering was used to provide a supplementary information about the structural organization of NFC suspensions. The statistical average diameter of 4.8 nm was determined from the scattering data for the NFC swollen in water.
KeywordsNanofibrillated cellulose (NFC) Microfibrillated cellulose (MFC) TEMPO-oxidized cellulose nanofibers (TOCN) Rheology Wall-slip Shear banding
This work has been carried out within the framework of International Doctoral School in Functional Materials (IDS-FunMat, Erasmus Mundus) and was funded by French Ministry of Higher Education and Research. We would like to express our gratitude to European Synchrotron Radiation Facility (ESRF) and particularly to Theyencheri Narayanan for the support with SAXS measurements. We thank to Domsjö Fabriker AB for providing the cellulose pulp sample. Laboratoire Rhéologie et Procédés (LRP) and Laboratoire Génie des Procédés Papetiers (LGP2) are a part of the LabEx Tec 21 (Investissements d’Avenir—Grant Agreement No. ANR-11-LABX-0030) and PolyNat Carnot Institute (ANR-11-CARN-030-01). LGP2 is also a part of Energies du Futur Carnot Institute (ANR-11-CARN-007-01).
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