Isolation and characterization of cellulose nanocrystals from garlic skin

Abstract

For the value-added utilization of underutilized agricultural by-products, garlic skin obtained abundantly in the food processing industry has been tested as a new source of cellulosic materials. Cellulose microfibers (CMF) and cellulose nanocrystals (CNC) were isolated from garlic skin fibers by alkali treatment and acid hydrolysis. The crude fiber, CMF, and CNC of garlic skin were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Transmission electron microscopy (TEM). Most of the lignin and hemicellulose was removed after the chemical treatment, and the degree of crystallinity of the CMF and CNC was increased compared with the crude fiber. The degree of crystallinity was 35%, 45%, and 63% for the crude fiber, CMF, and CNC, respectively. The cellulose nanocrystals exhibited spherical in shape with the size of 58–96 nm. The thermal stability of the CMF increased significantly, but that of CNC decreased slightly due to the introduction of sulfate groups into the cellulose crystals during acid hydrolysis. The nanocrystals had a high potential to be used as reinforcing filler for the preparation of bionanocomposites.