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 language | American English |
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Pages (from-to) | 2778-2791 |
Number of pages | 14 |
Journal | Green Chemistry |
Volume | 23 |
Issue number | 7 |
DOIs | |
State | Published - 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