Tailorable Cellulose II Nanocrystals (CNC II) Prepared in Mildly Acidic Lithium Bromide Trihydrate (MALBTH)

Ning Li, Huiyang Bian, J. Y. Zhu, Peter N. Ciesielski, Xuejun Pan

Research output: Contribution to journalArticlepeer-review

31 Scopus Citations

Abstract

Preparing cellulose II nanocrystals (CNC II) requires a polymorph transformation of natural cellulose I feedstocks. The transformation is usually achievedviaa process such as mercerization or dissolution-regeneration. This study demonstrated a new method to prepare CNC II directly from bleached kraft pulp (BKP, a commercially available cellulose I feedstock) in a mildly acidic lithium bromide trihydrate (MALBTH) system, a concentrated (∼61 wt%) solution of LiBr in water with a very low concentration (2.5 mM) of sulfuric acid. First, the BKP was treated in the MALBTH system to generate a cellulose II hydrolysis solid residue (CHR) with a yield of 64-86%, during which the selective hydrolysis of disordered cellulose and the polymorph transformation were completed simultaneously. Then, subsequent oxidation of the CHR by ammonium persulfate (APS, 0.1-0.6 M) resulted in the CNC II with high yield (up to 62%), high crystallinity (over 90%), rich surface carboxyl group (0.3-1.2 mmol g−1cellulose), excellent colloidal stability (up to −59 mV zeta potential), and high thermal stability. The CNC II had a tunable length (26-57 nm), determined by the conditions of the MALBTH hydrolysis and the APS oxidation, but similar lateral dimension (8-10 nm). The characterization of the CHR by wide-angle X-ray diffraction and Fourier transform infrared spectroscopy verified the polymorphic transformation from cellulose I to II during the MALBTH treatment. The swelling of the BKP in the MALBTH enabled cellulose crystallites to slide and reassemble, which completed the rearrangement of cellulose chains from parallel to anti-parallel conformation (polymorph transformation from cellulose I to II). This study provided an efficient and green method to produce cellulose II nanocrystals with controllable aspect ratiosviathe simultaneous hydrolysis and polymorph transformation of cellulose I feedstocks.

Original languageAmerican English
Pages (from-to)2778-2791
Number of pages14
JournalGreen Chemistry
Volume23
Issue number7
DOIs
StatePublished - 7 Apr 2021

Bibliographical note

Publisher Copyright:
© The Royal Society of Chemistry 2021.

NREL Publication Number

  • NREL/JA-2800-79131

Keywords

  • ammonium persulfate oxidation
  • amorphous cellulose hydrolysis
  • molten salt hydrate
  • nanocellulose
  • polymorph transformation

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