Controlling the transparency and rheology of nanocellulose gels with the extent of carboxylation

TEMPO and periodate are combined in a one-shot reaction to oxidise cellulose and produce nanocellulose gels with a wide range of degree of substitution (DS). Highly-oxidised cellulose nanofibres with a high charge of −80 mV were produced. The strong electrical repulsion between TEMPO-periodate oxidised nanofibres (TPOF) results in the formation of well-separated nanofibres with a diameter of 2−4 nm, albeit depolymerised due to high oxidation. TPOF produces highly-transparent gels due to smaller aspect ratio and high surface charge. These properties induce a reduced viscosity and moduli of the gels by decreasing fibre entanglement. TPOF gels are more stable at basic pH and high ionic strength than TEMPO-oxidised gels due to their higher surface charge. Freeze-dried TPOF gels also exhibit remarkable water holding capacity due to enhanced immobilisation of water molecules. The excellent optical properties of the highly transparent gel for red blood cells analysis open new possibilities in diagnostics application.