Preparation of Nanocellulose via Transition Metal Salt-Catalyzed Hydrolysis Pathway

Abstract

Nanocellulose was successfully prepared from microcrystalline cellulose (MCC) via nickel salt-catalyzed hydrolysis under mild reaction conditions of 45 °C for 15 min. The mild acid nickel salt-catalyzed hydrolysis was able to selectively depolymerize the amorphous regions of cellulose and retain its crystalline region, thus improving the crystallinity of the treated product at the nanoscale up to 80%. FTIR analysis confirmed that the basic cellulose structure of inorganic metal salt-treated products was maintained and that no derivative was formed. Furthermore, the synthesized Ni-treated nanocellulose (NTC) products appeared in the form of cluster fragments with spider-web-like appearance (fiber diameter of 10 to 60 nm and fiber length of 300 to 600 nm), thus providing aspect ratios in the range of 7.96 to 9.11. In addition, NTC products exhibited relatively higher thermal stability as compared to MCC because of the presence of high crystallinity phases and the absence of impurities (such as nitrate ions) on the nanocellulose surface. Thus, the present study concluded that nickel-based inorganic salt is an efficient and selective catalyst for the hydrolysis of MCC with high simplicity in operation and short preparation time.