Drying-induced bending deformation of cellulose nanocrystals studied by molecular dynamics simulations

Drying cellulosic materials from their water-swollen state can collapse their ultrastructure and alter their macroscopic material properties such as mechanical strength and water-retention ability. However, at the single-crystal or molecular level, little is known about the deformation of cellulose upon drying. We thus investigate herein the drying-induced deformation of a cellulose crystal by using an atomistic molecular dynamics simulation that considers a hydrated system composed of two short cellulose crystals, a lower one fixed to a flat substrate and an upper one free to deform. To mimic vacuum drying, the water is gradually removed from the system. As the drying proceeds, the upper cellulose crystal bends and forms a tight contact with the lower cellulose crystal. This result underlines the importance of lateral deformation of cellulose crystals in the collapse of the cellulose ultrastructure and provides insights into the molecular mechanisms responsible for modifying the properties of cellulose materials.