Dispersing uncharged cellulose nanocrystals through a precipitation surface modification route using oligosaccharides

Abstract

The trend to replace petrochemical materials with sustainable alternatives has increased interest in plant-based particles like cellulose nanocrystals (CNCs). A remarkably simple and effective method for producing uncharged CNCs involves solid-state hydrolysis using hydrochloric acid gas (HCl(g)). While this chemistry results in HCl(g)-CNCs produced at very high yields (>97%), they cannot be easily dispersed as individual nanoparticles. Here, the potential of using oligosaccharide surface modifiers as dispersing agents for HCl(g)-CNCs to yield isolated and colloidally stable CNCs is investigated. Importantly, the cello-oligosaccharide surface modifiers used were externally-produced and had very low charge. By increasing the amount of oligosaccharide added relative to HCl(g)-CNCs, it was possible to proportionally increase the degree to which the CNC surface was modified. This surface modification resulted in ubiquitous improvements to the dispersibility of HCl(g)-CNCs. We also applied this surface modification to uncharged CNCs produced using aqueous hydrochloric acid (i.e., HCl(aq)-CNCs) and observed marked improvements to their colloidal stability in aqueous media that did not trend with increasing charge but rather with oligosaccharide content. Overall, this study indicates the applicability of an easily scalable modification route that opens the door for expanded CNC functionality and tailoring colloidal stability of these versatile materials.