Synthesis of nanocrystalline cellulose via ammonium persulfate-assisted swelling followed by oxidation and their chiral self-assembly
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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.
KeywordsOne-step synthesis Nanocrystalline cellulose Ammonium persulfate Swelling Oxidation Spindle-shaped helical structure Chiral self-assembly
This work was financially supported by National Natural Science Foundation of China (Grant Nos. 21566014 and 21766016), China Postdoctoral Science Foundation (Grant No. 2019M653845XB) and Postdoctoral Research Funding of Kunming University of Science and Technology (Grant No. 10988880). H. Wang special thanks to Prof. Zhuang, KMUST for providing the facilities for POM measurements. M. Pudukudy gratefully acknowledges the financial support fromYunnan Province Postdoctoral Research Funding and Yunnan Province Postdoctoral Orientation Training Funding.
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Conflict of interest
The authors declare that they have no conflict of interest.
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