Electrostatic-based separation system for negatively charged cellulose nanocrystals

• A filtration-free electrostatic-based separation apparatus was developed. • Bacterial cellulose nanocrystals (BCNCs) migrated via electrophoretic movement. • Physico-chemical properties of BCNCs were preserved after electrostatic separation. • Preconcentrated BCNCs gel with a solid content up to 7.5% (w/w) could be obtained. A filtration-free and non-destructive electrostatic-based separation and preconcentration system for bacterial cellulose nanocrystals (BCNCs) dispersed in aqueous media have been developed by harnessing the electrostatic interactions between negatively charged BCNCs and the positively charged graphite electrode. BCNCs are extracted from Nata de Coco by sulfuric acid hydrolysis and exhibit an average hydrodynamic diameter of 342 nm and an average zeta potential of −56 mV. The extracted BCNCs exhibit needle-like morphology as characterized by transmission electron microscopy. The electrostatic separation apparatus consists of three main components including a programmable direct-current power supply, two graphite electrodes arranged in a parallel-plate configuration, and a 3D-printed electrode holder. Upon applying uniform electric fields with constant electrical voltages, BCNC particles are subjected to electrophoretic motion and accumulated on the graphite anode as an opaque white gel. The deposited BCNC gel could be easily separated from the dispersing medium. The mass concentration of the separated BCNC gel could be enhanced up to 7.5% (w/w). The quantity of deposited BCNC particles on the graphite anode tends to increase with the applied electric field strength, the treatment duration, and the thickness of the graphite electrode. Under optimized conditions, the developed process does not cause significant alterations in morphology, chemical functional groups, surface charge, colloidal stability, and crystallinity of the BCNCs as confirmed by transmission electron microscopy, FT-IR spectroscopy, dynamic light scattering, zeta-potential analysis, conductometric titration, and X-ray diffraction. The electrostatically separated BCNCs could be redispersed in various polar solvents and exhibit good colloidal stability.