Specific water uptake of thin films from nanofibrillar cellulose

Swelling of NFC films was surveyed by quartz crystal microbalance with dissipation monitoring coupled with H2O/D2O exchange and surface plasmon resonance. The influence of charged groups on swelling was investigated by neutralizing the charge of NFC with cationic polyelectrolytes or increasing the charge with carboxymethyl cellulose (CMC). The solid content of the porous NFC film was <50%. In the swollen state, a film contained only similar to 15-30% cellulose. Adsorption of cationic polyelectrolytes decreased the ability of the film to bind water by a maximum of 20% indicating that the contribution of charge to the swelling of NFC is moderate. Annealing of the film also caused a 20% reduction in its water uptake. Yet annealing after adsorption of cationic polyelectrolytes decreased the water-binding ability of the film by similar to 50%. Charge increase by CMC adsorption caused additional swelling of the NFC film while subsequent charge neutralization by cationic polyelectrolytes reduced the water content below the control reference.