Influence of electrostatic interactions on the dewatering and mechanical properties of cellulose nanofiber/precipitated calcium carbonate composite films

When mixtures of cellulose nanofibers and pigments are dried, plastic-like structures are generated that have the potential to replace single-use plastics in many applications. However, the water is often difficult to remove by mechanical methods. Here, the influence of the zeta potential of the pigment on the dewatering behavior of cellulose nanofibers-precipitated calcium carbonate suspensions, as well as on the mechanical properties of the films, was determined. The addition of cationic precipitated calcium carbonate increased the water drainage rate by 1.4–2.7 times, compared to anionic precipitated calcium carbonate. For example, a 50/50 wt% cellulose nanofibers/cationic precipitated calcium carbonate mixture was able to achieve higher solids in the filter cake in half the time that is required for a 50/50 wt% cellulose nanofibers /anionic precipitated calcium carbonate suspension. Turbidity measurements confirm the adsorption of cellulose nanofibers onto the cationic precipitated calcium carbonate. The increase in the water drainage rate of the cellulose nanofibers /cationic precipitated calcium carbonate suspensions is likely caused by this adsorption that leads to free water in the suspension. This electrostatic attraction between the cationic precipitated calcium carbonate and anionic cellulose nanofibers also hinders the hydrogen bonding of the system during drying resulting in Young’s moduli that are 12–17% lower for the cellulose nanofibers/cationic precipitated calcium carbonate films compared to the cellulose nanofibers/anionic precipitated calcium carbonate films. Graphical abstract