The thermal stability of cellulose nanocrystals (CNCs) is most often evaluated via thermogravimetric analysis, in which dried CNCs are heated in an inert atmosphere. While this can be relevant for applications which use dried CNCs, it cannot predict the performance of aqueous CNC suspensions at high temperatures. To further understand these aqueous systems, CNCs with varying surface chemistry, surface charge density, counterion and size were subject to hydrothermal treatment and subsequently analyzed. Changes in suspension properties such as colour, turbidity, colloidal stability and aggregate size, as well as CNC properties including degree of crystallinity and degree of polymerization, were evaluated before and after heat treatments. CNC surface chemistry, which is generally a function of the production route, heavily influenced the performance of the suspensions at high temperatures. CNCs with sulfate half-ester groups underwent rapid desulfation at temperatures as low as 150 °C. Without electrostatic stabilization, CNCs formed large aggregates and their suspensions became turbid. Despite the loss of colloidal stability, the physical structure of the CNCs remained intact and virtually no depolymerization of cellulose chains occurred. Conversely, by performing an oxidation and imparting carboxyl groups on the surface of the CNCs, significant changes in thermal stability were observed. Carboxylated CNCs maintained colloidal stability at high temperatures due to continuous electrostatic repulsion; however, heated suspensions were heavily discoloured. Overall, this study provides insights into the ability of CNCs to withstand hydrothermal treatments and describes the suspension properties which can be expected after such treatments. These new insights can be used to expand the use of CNC suspensions in industrial processes with high operating temperatures.

Effects of hydrothermal treatment on cellulose nanocrystal properties

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.