Theoretical and Experimental studies of chitin nanocrystals treated with ionic liquid or deep eutectic solvent to afford nanochitosan sheets

•IL pretreatment was able to break partially the crystal leading to the formation of nanochitosan sheets.•DES-pretreatment was neither able to break the crystal nor to disturb the intra- and intermolecular hydrogen bonds.•Deacetylation reaction performed on IL-pretreated chitin nanocrystals was the strongest.•Combination of H-bonding capability and strong electrostatics in IL is mandatory for efficient chitin dissociation in silico.