Use of Polyelectrolyte Complexes as a Binding Agent in the Granulation Process of Titania Particles

The process of powder granulation by the colloidal way allows to shape millimetric ceramic spheres with a homogeneous distribution in terms of size and shape. This process is based on the coalescence of agglomerates in diluted media. This occurs because grains are partially covered by a binding agent. The system studied is based on a titania (anatase) powder granulated by a mixed system of a polyanion, the poly(sodium 4-styrenesulfonate), and a polycation, the chitosan. The reaction of condensation between the two polyelectrolytes leads to in situ formation of filaments acting as efficient binding agents. By selecting the suitable ratio between the two polymers, this formulation makes it possible to granulate the titania powder while retaining its purity. Organic filaments favor the coalescence step and also prevent the formation of cracks within the granules. The microstructural arrangement results from a snowball growth mechanism and from the migration of the grains due to the capillary forces occurring during the drying stage.