Changes in the molecular structure of cellulose nanocrystals upon treatment with solvents

The morphological properties of nano cellulosic materials affect their industrial applications significantly. Solvents are commonly used in treating cellulosic materials in altered applications. In this work, the treatment of cellulose nanocrystals (CNCs) with dimethyl sulfoxide (DMSO) (99.5%) and N-methyl morpholine-N-oxide (NMMO) (50%) was investigated comprehensively under different conditions to evaluate the effect of solvent treatment on the properties of CNCs. A partial polymorphic transition of cellulose I to II was observed when CNCs were treated with the solvents. The temperature of the treatment was more influential than the time of the treatment in altering the CNC properties. XRD, light scattering, and wettability analyses confirmed that the partial dissolution of CNCs in solvents reordered the cellulosic chains from parallel to antiparallel. It also made more hydroxyl groups accessible on CNCs for hydrogen bonding, facilitating the CNC aggregation and instability in solutions. The XPS analysis revealed a remarkable alteration in the relative amounts of components in C 1s, reflecting transformation in the chemical bonds from C=O/O–C–O to C–O on the CNC surface. The increase in the hydroxyl group of CNCs also improved the water-uptake and hydrophilicity of CNCs when they were treated with solvents. The results of this work would suggest that the alteration in the CNC characteristics should be considered when selecting solvents for developing industrial applications for CNCs.