Terahertz time-domain spectroscopy as a novel tool for crystallographic analysis in cellulose: tracking lattice changes following physical treatments

The author's series of studies aimed to explore the potential of terahertz time-domain spectroscopy (THz-TDS) in cellulose crystallography research, as THz radiation can detect most intermolecular vibrations and respond to the lattice phonons. In this study, we used THz-TDS and X-ray powder diffraction (XRD) to meticulously trace the changes in the four types of cellulose after ball milling. The most captivating observation was the crystal transition from cellulose I to cellulose II (cellulose I treated with 10% NaOH), demonstrating reduced crystallinity but an increased conversion rate to cellulose II after ball milling. Moreover, we used scanning electron microscopy to observe the morphological changes of the treated cellulose samples after ball milling in detail, and gel permeation chromatography was used to determine the molecular weight, probing the correlation between morphological and molecular weight changes with the THz 2nd derivative absorption spectrum and the XRD pattern.