Stabilization of emulsions (and foams) with nanocellulose materials

Cellulose nanomaterials are environmentally sustainable, renewable, abundant and biodegradable. They offer an alternative to many materials based on fossil resources and, hence, research on manufacture, properties and applications of cellulose nanomaterials has developed explosively during the last decade. This lecture gives an overview of two applications of cellulose nanomaterials: the properties of cellulose nanofibrils (CNF), cellulose nanocrystals (CNC) and bacterial cellulose as stabilizers of particle stabilized emulsions (Pickering emulsions) and foams. Both CNF and CNC can be used to prepare strong, extremy lightweight solid foams. Using different methods to render the particle surfaces hydrophobic CNF and CNC can be used stabilize w/o emulsions with controlled particle size in a very wide range of sizes. In this context the fact that surface hydroxyl groups are ideal targets for chemical functionalization is one of the great advantages of CNFs and CNCs. More hydrophilic particles tend to stabilize o/w emulsions. Shape, charge and dosage of CNF or CNC as well as the nature of the oil phase and the oil/water ratio strongly affect the properties of the emulsions (stability, droplet size and size distribution, rheology etc.). The stabilizing mechanism seems to be related to the ability of the CNF or CNC to form stable films at the o/w interface and, accordingly, they primarily act as stabilizers against coalescence rather than flocculation.