Sulfuric acid alcoholysis as a way to obtain cellulose nanocrystals

The lack of an alternative universal method for obtaining cellulose nanocrystals (CNCs), that would replace traditional sulfuric acid hydrolysis, encourages researchers to look for new methods and approaches. At the same time, alcoholysis of cellulose has long been known as a method of obtaining various alkyl glycosides and products of their further alcoholysis. In this paper, the authors propose to use controlled alcoholysis of cellulose in a medium of simple alcohols for CNC synthesis. Specifically, in this study, CNCs are prepared by controlled sulfuric acid alcoholysis of sulfate cellulose in a medium of four aliphatic alcohols (methanol, ethanol, propanol, and butanol-1). The paper also discusses the possible mechanism of cellulose alcoholysis during CNC preparation and shows that, in contrast to hydrolysis, cellulose alcoholysis can produce CNCs with a higher yield and under milder conditions (at a lower acid concentration). The physicochemical properties of the CNCs synthesized are studied. On the whole, the properties of the CNCs obtained by alcoholysis and hydrolysis are found out to be similar. However, alcoholysis is shown to produce CNC particles with a higher surface charge, which increases the colloidal stability of aqueous CNC suspensions and can be used to study their liquid crystal properties. Under the given conditions of CNC synthesis in alcoholic media (concentration of sulfate cellulose suspension of 0.025 g/mL, temperature of 50 °C, duration of 2 h), butanol-1 makes it possible to achieve the maximum possible CNC yield of 60%.