Sequential extraction of carbohydrates and lignin from agricultural waste and their structural characterization

Abstract

This work reports on the extraction and characterization of carbohydrates such as cellulose, cellulose nanofibres, hemicellulose, and lignin from agricultural waste, i.e. maize stalks and sugarcane bagasse. The chemical compounds were extracted by hot water extraction (HWE) followed by alkaline extraction with 10 wt.% of sodium hydroxide (NaOH). Cellulose nanofibres (CNF) were isolated by mechanical grinding the cellulose fraction using a supermass colloider. The characteristics of the different fractionated components were investigated using nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and X-Ray diffraction (XRD). The removal of the hemicellulose, lignin and extractives were confirmed quantitatively by TAPPI standard methods. It was observed that the cellulose content and its crystallinity increased after treating maize stalks and sugarcane bagasse with hot water extraction and alkali treatment. The thermal stability of cellulose also improved after treatments. Transmission Electron Microscopy (TEM) results confirmed that web-shaped CNF were successfully extracted from the cellulose obtained from sugarcane bagasse and maize stalks. The dimensions of the CNF ranged from 5 to 30 nm in width and a few microns in length. In future studies, the fractionated hemicellulose, lignin and (micro and nano) cellulose will be used as reinforcements in the development of biocomposite materials.