Effects of acid treatments on bamboo cellulose nanocrystals

Abstract

The production of nanocellulose with controlled structure from plant sources with easy availability and good sustainability is very important in science and engineering. In this work, the isolation of cellulose from bamboo and the effects of the hydrolysis of different acids on the morphology, structure, and properties of the resultant cellulose and cellulose nanocrystals were investigated. Bamboo cellulose (PHC) was first isolated from raw bamboo powder by alkali and consecutive bleaching treatments. Cellulose crystallites were then prepared by the controlled hydrolysis of PHC in acid solutions. The samples were characterized by using thermogravimetric analysis, Fourier transform infrared spectroscopy, powder X-ray diffraction, laser particle size analyzer, Scanning electron microscopy, and Transmission electron microscopy. Cellulose nanocrystals prepared from the hydrolysis of the isolated bamboo cellulose in the sulfate acid, hydrochloric acid, phosphoric acid, or acetic acid solution had the length of 3-200 nm, 20-85 nm, 20-40 nm, and 6.5-20 nm, respectively. Nanocrystals made by the uses of sulfuric acid and phosphoric acid possessed higher crystallinity and lower thermal stability than those by the uses of hydrochloric acid and a mixture of acetic acid and nitric acid. Results suggested the type of acids significantly influenced the structure, morphology, and thermal stability of cellulose crystallites. The anions in the acid solution also contributed to those differences because they affected the swelling of cellulose chains and breakage of hydrogen bonds in cellulose. The findings indicate that a judicious choice of pretreatment of the cellulose and its moieties can be used for the production of different cellulose nanocrystals.