Synthesis of nanocrystalline cellulose via ammonium persulfate-assisted swelling followed by oxidation and their chiral self-assembly

Abstract

A single-step ammonium persulfate (APS)-assisted swelling, followed by oxidation, can prepare nanocrystalline cellulose (NCC) from cotton linters. The APS-swelling is the critical step in the process, and the effects of swelling time, temperature and solid–liquid ratios were thoroughly investigated. The optimal conditions for NCC preparation were a swelling time of 3.0 h, a swelling temperature of 25 °C, and a solid–liquid ratio of 1:50. Upon heating at 60 °C, the persulfate enters the amorphous region of the cellulose and produces active SO4·− and H2O2, which effectively attack the two-phase structure of cellulose and oxidize the –OH group at the C-6 position. The swelling temperature of 25 °C plays a crucial role in breaking the hydrogen bonds between the molecular chains of cellulose. It permits the preparation of NCC with a high yield and crystallinity index. The crystalline structure of cellulose Iβ did not change after APS swelling and oxidation. The atomic force microscopic analysis confirmed the formation of spindle-shaped particles with a helical structure. Upon natural evaporation of the NCC suspension, brittle films were obtained, which exhibited a left-hand layered structure and high iridescence with a fingerprint-texture. These materials can be applied as strength additives and chiral templates.