Mechanoenzymatic hydrolysis of cotton to cellulose nanocrystals Sandra Kaabel, Eero Kontturi and Mauri Kostiainen Department of Bioproducts and Biosystems, Aalto University, Finland Solid-state or high solid-loading reaction conditions, akin to the natural setting of cellulases, chitinases and xylanases, have been shown to make hydrolysis of the respective biopolymers more efficient [1–3] and can enhance enzymatic hydrolysis of synthetic polymers, such as high-crystallinity polyethylene terephthalate. [4] However, tailoring the solid-state biocatalytic approach targeting high yield of cellulose nanocrystals (CNCs) has not been sufficiently explored. [5] Biocatalytic solid-state methods could provide an environmentally benign alternative to the predominantly used acid-hydrolysis, [6] by reducing the amount of water and energy used, using renewable catalysts and eliminating corrosive wastes. [7,8] We systematically investigated the biocatalytic synthesis of CNCs, varying the source of cellulose, the biocatalyst and the solid-state reaction conditions combining mechanochemistry and accelerated aging. Size-exclusion chromatography, powder X-ray diffraction and transmission electron microscopy revealed that while the dispersibility of the resulting enzymatically hydrolyzed (uncharged) cellulose was poorer in water than the charged CNCs from acid-hydrolysis, the obtained nanoscale aggregated material was highly crystalline, with a degree of polymerization ( DP n ) similar to that obtained by acid catalysis. Aside from building towards a greener route for the synthesis of CNCs, the presented research provides insight into the key parameters influencing the solid-state enzymatic hydrolysis and the nature of the resulting material. References 1. F. Hammerer, L. Loots, J.-L. Do, J. P. D. Therien, C. W. Nickels, T. Friščić, K. Auclair, Angew . Chem. Int . Ed . 2018 , 57 , 2621–2624. 2. S. Ostadjoo, F. Hammerer, K. Dietrich, M. J. Dumont, T. Friščić, K. Auclair, Molecules 2019 , 24 , 4206. 3. J. P. D. Therien, F. Hammerer, T. Friscic, K. Auclair, ChemSusChem 2019 , 12 , 3481-3490. 4. S. Kaabel, J. P. D. Therien, C. E. Deschênes, D. Duncan, T. Friščic, K. Auclair, Proc . Natl . Acad . Sci . U . S . A . 2021 , 118 , e2026452118. 5. Q. Zhang, Z. Lu, C. Su, Z. Feng, H. Wang, J. Yu, W. Su, Bioresour . Technol . 2021 , 331 , 125015.
6. O. M. Vanderfleet, E. D. Cranston, Nat . Rev . Mater . 2021 , 6 , 124–144. 7. S. Kaabel, T. Friščić, K. Auclair, ChemBioChem 2020 , 21 , 742–758. 8. F. Hajiali, T. Jin, G. Yang, M. Santos, E. Lam, A. Moores, ChemSusChem 2022 , 15 , e202102535.
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