Preparation of nanocellulose by hydrolysis catalysedusing salts with different Fe valency

The production of cellulose nanocrystals (CNCs) from vegetable fibres and residues has been intensely investigated due to the properties of high crystallinity and specific surface area of these nanofillers. The most common method of obtaining CNCs is by acid hydrolysis with inorganic acids; however, this method can lead to uncontrolled depolymerisation of the cellulose. Thus, this article examines the use of Lewis acids (FeSO4, Fe2(SO4)3 and FeCl3) as co-catalysts in the acid hydrolysis process and compares their impact on the yield, reduction of particle size and crystallinity index of the CNCs. The results show that the presence of Fe2(SO4)3 and FeCl3 improved the yield (50 and 27%, respectively) and decreased the particle size (632 and 66 nm, respectively) of the CNCs obtained in the hydrolysis process. On the other hand, the crystallinity index values were similar to that of microcrystalline cellulose (MCC), which was probably due to the severe conditions of the hydrolysis process that was used. The scanning transmission microscopy (STEM) images showed a spherical morphology for the CNCs obtained by both inorganic acid and Lewis acids; once again, this was probably due to the severe hydrolysis conditions. Thus, the presence of Lewis acids in the hydrolysis process makes it more efficient because it increases the efficiency of the hydrolysis in a less corrosive environment and with less probability of depolymerisation of the cellulose.