Preparation and characterization of dialdehyde cellulose nanocrystals from the waste nutshell

Efficient use of the entire lignocellulosic biomass is important for biorefinery sustainability, especially considering the extraction of high value-added products, such as nanocellulosic materials. In this study, the raw fibers were subjected to bleaching and alkali treatments to obtain cellulose, followed by sodium periodate (NaIO4) oxidization and sulfuric acid (H2SO4) hydrolysis without mechanical treatment for the isolation of dialdehyde cellulose nanocrystals (CNCs) from nutshell of Peanut and Sunflower seed. The resultant nanocrystals were characterized for structural changes using transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectrometer, X-ray diffractometer (XRD), and thermal gravimetric analysis (TGA). The aldehyde content of the CNCs was also investigated. XRD analysis proved that the crystallinity index (CrI) decreased after sequential oxidation. However, the cellulose I structure was maintained with a CrI of 55% and 62%, respectively. FTIR analysis confirmed the total removal of non-cellulosic compounds from microfibers’ surface and their partial oxidation after aldehyde functionalization. TEM results showed that rod-shaped CNCs with an average length and width of 142.93 ± 56.46 nm and 11.11 ± 3.07 nm, respectively, were successfully isolated. The thermal properties of CNCs indicated early dehydration with high char formation, while the high thermal stability was 231 °C (Tmax). The findings demonstrated the effective extraction of cellulose nanocrystals from nutshell. This study will not only aid in the sustainable conversion of food industry waste into a value-added product but also promote the circular economy. This may further help to reduce global emissions and address the key challenges of climatic change. Graphical abstract