Preparation and Characterization of Sisal Cellulose Nanocrystals-Assembled Film

Cellulose nanocrystals (CNCs) extracted from sisal by acid hydrolysis were used to prepare the film with a chiral nematic phase structure by evaporation-induced self-assembly method. The effects of different acid reaction times on the morphology of sisal CNCs and the optical and mechanical properties of CNC films were investigated. Transmission electron microscopy (TEM), surface charge, and scanning electron microscopy (SEM) analysis showed that as the reaction time of acid hydrolysis increased from 30 to 90 min, the surface charge of CNCs increased from 0.116 to 0.285 mmol g(-1) and the average length decreased from 193.6 to 100.1 nm. Sisal CNCs can self-assemble to form the film with a chiral nematic phase structure by the evaporation-inducing method. The combination of the above two aspects resulted in an increase and then a decrease in the helical pitch of CNC films. UV-Vis spectra and polarized light (POM) analysis of the CNC films revealed that the change in helical pitch can affect the color change of CNC films from blue to red and then to yellow-green. The effects of different reaction times on the nanomechanical and macroscopic mechanical properties of CNC films are reported. At the reaction time of 60 min, the macroscopic mechanical properties of the CNC film were good with a tensile strength of 43.59 MPa. This research could provide a good option for the extraction and application of sisal CNCs and create higher value-added products of sisal.