Cellulose nanocrystals with CO2-switchable aggregation and redispersion properties

Cellulose nanocrystals (CNCs) were modified through a one-step 1,1'-carbonyldiimidazole (CDI)-mediated coupling with 1-(3-aminopropyl)imidazole (APIm). The CNC-APIm prepared could be readily dispersed into carbonated water. Subsequent sparging of N-2 into the dispersion gave rise to the formation of aggregates. This dispersion/aggregation cycle was reproducible by alternatively sparging CO2/N-2 into the CNC-APIm aqueous dispersion, indicating that the chemically bonded imidazole groups on the CNC surface were stable and could respond to the CO2 stimulus in an effective and repeatable manner. Moreover, above certain concentrations (around 5.5-10 mg/ml) the CNC-APIm dispersion could be gelled in the presence of N-2 while subsequent sparging CO2 could break the gel and regenerate a low viscosity CNC-APIm dispersion. This dispersion-gelation conversion was reversible by alternatively switching between sparging CO2 and N-2. To our knowledge, the present work is the first report of CO2-switchable CNCs.