Rheology of aqueous dispersions of Laponite and TEMPO-oxidized nanofibrillated cellulose

Both laponite and TEMPO-oxidized nanofibrillated cellulose (TEMPO-NFC) can find several applications in various fields (from industrial to biomedical one) in virtue of their peculiar features and rheological properties displayed in aqueous phases. Structural states of laponite dispersions strongly depend on concentration and ionic strength. When attractive and repulsive interparticle interactions are so effective that they lead to generate arrested states (attractive gel or repulsive glass), the rheological behavior of the dispersion undergoes a sharp transition, from quasi-Newtonian to markedly shear thinning and viscoelastic. Aqueous suspensions of TEMPO-NFC show stable gel properties at low solids content, due to the hygroscopic character of the cellulose as well as the high aspect ratio and specific surface area of nanofibrils. TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) mediated oxidation pretreatment, which converts the primary alcohol groups of the cellulose D-glucose units into carboxylate groups, provides the necessary electrostatic repulsion between the fibrils to prevent agglomeration. The present work is concerned with aqueous laponite-TEMPO NFC systems and is aimed at examining how much the content and proportion of both components affect the viscoelastic and flow properties of the mixed system at different times from sample preparation. The synergistic effects produced by blending are eventually compared with those observed for mixed Laponite-soluble polymer systems.