Influence of temperature and humidity on nano-mechanical properties of cellulose nanocrystal films made from switchgrass and cotton

• Mechanical properties of CNC casting films were greatly affected by temperature and humidity.
• Higher aspect ratio of CNC makes its CNC films have higher mechanical properties.
• Switchgrass CNC was prepared and characterized.

Two kinds of cellulose nanocrystals (CNCs) were prepared by sulfuric acid hydrolysis from switchgrass and from cotton. The morphology of CNC and casting CNC films were characterized by atomic force microscopy (AFM) and polarized optical microscopy (POM). Nano-indentation was used to measure the nano-mechanical properties of the CNC films, and the influences of humidity and temperature conditions during testing were investigated. The results showed that switchgrass CNC has a higher aspect ratio than cotton CNC; under POM, the switchgrass CNC films showed obvious liquid crystal characteristics. Mechanical testing showed the modulus (Er) and hardness (H) of switchgrass CNC films to be higher than those of the cotton CNC films. Furthermore, the mechanical properties of both CNC films increased sharply with reducing humidity or increasing temperature.