Interfacial Mechanical Behavior of Cellulose Nanocrystals and Chitosan

Natural nanocomposites based on cellulose and chitosan have attracted much attention as alternatives to petroleum-based plastics. However, much less is understood about the interfacial properties between cellulose nanocrystals (CNCs) and chitosan that are essential for tuning the thermomechanical properties of CNC–chitosan nanocomposites. Here, we systematically investigate the interfacial behavior of CNC–CNC and CNC–chitosan systems by using atomistic molecular dynamics. The introduction of an interface has a significant influence on the structure and molecular mobility of chitosan near the interface, while it has a negligible effect on the CNC–CNC system due to its layered structure in the traverse directions perpendicular to the chain direction. The tension separation simulations demonstrate that in comparison with the CNC–CNC interface, the interfacial adhesive strength and stiffness of the CNC–chitosan interface decease but still maintain relatively high values. The hydrophilic (110) and (010) surfaces of CNC exhibit a better dispersion factor (∼0.7) in the chitosan matrix than the hydrophobic (100) surface. Moreover, the shear responses indicate that the underlayer CNC exhibits a stick–slip behavior at the CNC–CNC interface, while a smooth sliding is observed at the CNC–chitosan interface, leading to a smaller interfacial shear strength. With the insertion of chitosan as an intermediate layer at the CNC–CNC interface, the interfacial shear modulus progressively decreases with the increasing chitosan content for a chitosan thickness smaller than 9 nm, and it has a linear relationship with the reciprocal of molecular mobility of the chitosan layer. Our study provides fundamental insights into the influence of chitosan on the interfacial mechanical properties of CNCs and sheds light on the design of high-performance CNC–chitosan nanocomposites.