Cationic cellulose nanofibrils and anionic clays: colloidal stability and electrostatic interactions in water

Nanocomposites based on nanocellulose and natural clay minerals are gaining special interest due to their improved mechanical, optical, thermal, and barrier properties.¹ Stable dispersions are essential for achieving these desirable characteristics; therefore, it is essential to study the interactions that govern the colloidal behavior of the system. In this work, we evaluated the interactions between cationic cellulose nanofibrils (cCNF, 0.44 mmol/g) and anionic layered silicates, bentonite (MMT) or kaolin (KAO), in water. By zeta (ζ) potential measurements, good colloidal stability was observed in the pristine suspensions of cCNF and MMT (+52 and −34 mV, respectively), while KAO suspension presented poor stability (−18 mV). The addition of MMT to cCNF at concentrations far from the charge neutrality point (up to 70 wt.% clay) resulted in colloidally stable systems (ζ > +42 mV), indicating that electrostatic complexation minimally affected the stability of dispersion until this concentration. However, increasing MMT content to 80 wt.% caused a charge inversion in the ζ−potential to −24 mV, suggesting that the neutral point lies between 70 and 80 wt.% of clay. In contrast, no charge inversion occurred in mixtures of cCNF and KAO at the studied mass ratios. Preliminary experiments conducted in quartz crystal microbalance with dissipation monitoring showed strong interfacial interactions between the components. The frequency decrease upon adsorption of the KAO layer on cCNF was more significant than that observed upon adsorption of MMT on cCNF. Also, an increase in dissipation upon adsorption in both systems indicates the formation of viscoelastic layers.² Further investigation is needed to better understand the forces involved in the interactions between cCNF and anionic clays.

1. L. Alves et al. Adv. Colloid Interface Sci., 2019, 272, 101994.

2. M. Ghanadpour et al. Applied Materials Today, 2017, 9, 229−239.