Structural variations of cotton cellulose nanocrystals from deep eutectic solvent treatment: micro and nano scale

The behavior of pressed poplar chemi-thermo-mechanical pulping (CTMP) without additive the focus of our study. Four CTMPs with decreasing lignin contents were prepared by the sodium chlorite/acetic acid method and the holocellulose, alpha-cellulose, pentosan and Klason lignin contents of the delignified CTMPs were determined. The surface composition, aggregation structure and microstructure of the delignified fibers were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscope (SEM), and the mechanical properties of the fiber material were investigated by means of tensile and bending tests. As shown by XPS, the lignin content of the Pr-CTMP surface layer firstly increased and then decreased as the lignin content of CTMP decreased. With the delignification time increased from 0 to 240 min, the crystallinity index (CrI) of CTMP increased from 60.1% to 65.7%.