IS MERCERIZATION THE ONLY FACTOR FOR (PARTIAL) POLYMORPHIC TRANSITION OF CELLULOSE I TO CELLULOSE II IN CELLULOSE NANOCRYSTALS?

Abstract

"The present study aims to investigate the influence of factors such as the source of cellulose and cellulose extraction and acid hydrolysis conditions on the partial polymorphic transition of Cellulose I to the allomorphic form Cellulose II in cellulose nanocrystals (CNCs). CNCs were obtained from cellulose fibers extracted from four agro-industrial residues in Ethiopia: teff straw (TS), enset fiber (EF), sugarcane bagasse (SB) and coffee hull (CH). The cellulose fibers were extracted under chlorine-free extraction conditions, comprising alkaline pretreatment (with 17.5% (w/v) sodium hydroxide), then hydrolyzed with 64% (w/w) sulfuric acid to synthesize the CNCs. The as-obtained CNCs were characterized with X-ray diffraction (XRD), Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The XRD results revealed the CNCs isolated from cellulose fibers of EF and SB contained Cellulose I and II allomorphs like their cellulose precursors, but no Cellulose II was found in CH-CNCs. Morphological and dimensional studies of the CNCs by TEM showed shorter needle-shaped nanoscale structures. Higher alkaline conditions, with 17.5% sodium hydroxide, might not necessarily contribute to the polymorphic transition in lignocellulosic materials with higher lignin content, as evidenced in CH. Generally, the formation of Cellulose I and II allomorphs in the as-obtained CNCs was dependent on the cellulose source and cellulose extraction conditions, and less influenced by sulfuric acid hydrolysis."