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Production of high lignin-containing and lignin-free cellulose nanocrystals from wood

Agarwal, Umesh P., Ralph, Sally A., Reiner, Richard S., Hunt, Christopher G., Baez, Carlos, Ibach, Rebecca, Hirth, Kolby C.
Cellulose 2018 v.25 no.10 pp. 5791-5805
Populus, acid hydrolysis, cellulose, crystal structure, hot water treatment, hydrophobicity, lignin, microscopy, nanocrystals, nanoparticles, spectroscopy, sulfuric acid, temperature, wood, wood fibers
A new method is described for producing high-lignin-containing and lignin-free cellulose nanocrystals from poplar wood (HLCNCs and LFCNCs, respectively). This was accomplished by first hydrothermally treating the poplar wood fibers at 170 °C for 45 min in a Parr reactor. For obtaining HLCNCs, the treated fibers were directly hydrolyzed by 64% sulfuric acid whereas for LFCNCs, the fibers were delignified prior to the acid hydrolysis. The CNCs thus produced were characterized using spectroscopy, microscopy, and diffraction techniques and compared with bleached kraft pulp-CNCs. The comparison indicated that while LFCNCs and pulp-CNCs had similar properties, the HLCNCs are expected to be superior for certain applications due to their hydrophobicity that was caused by presence of lignin nanoparticles. Lastly, results of the experiment where treatment temperature was varied during the hydrothermal treatment indicated that crystallinity of the CNCs produced from 200 °C treated poplar was higher compared to 170 °C treated substrate. This implied that CNCs from wood can be produced that have varying degree of crystallinity.