Abstract
Aqueous nanogels are notoriously difficult to dewater. An example of such a gel is that of a suspension of micro nanofibrillated cellulose, in which water is both bound to the fibrillar surface and held within the interfibril matrix. We demonstrate a phenomenon in which dewatering of nanocellulose based gel-like suspensions can be induced by adding a colloidal particulate component, which itself can undergo autoflocculation when suspended in water. The mechanism is exemplified by the addition of undispersed precipitated calcium carbonate, which in equilibrium remains stabilised in the gel, but when the gel mix is exposed to ultralow shear, acting below the yield stress, demixing of the combination between the nanofibrils and the autoflocculating pigment leads to separation of the unbound water phase. This novel mechanism is proposed to enhance the dewatering capability in general of complex gel-like water-holding suspensions.
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