Abstract
Given that terahertz (THz) radiation responds to intermolecular forces such as hydrogen bonds, THz time-domain spectroscopy (THz-TDS) has expanded possibilities in cellulose research. In this study, THz-TDS was used to investigate the crystallinity of three types of cellulose-based materials. Microcrystalline cellulose (MCC) and wood were ball milled at different times, and pseudo-wood was a mixture of MCC and lignin of different mass fractions. All the samples showed peaks at 3.04 THz in the THz mass absorption coefficient spectra. Further, the spectra from 2.79 THz to 3.32 THz were cut out and detrended by subtraction from a baseline. The integrated intensity of the detrended spectra showed a correlation with the mass fraction of lignin of the pseudo-wood samples, and ball milling time of the MCC and wood samples. The correlation was similar with the crystallinity index calculated from X-ray powder diffraction. Moreover, the original wood sample without ball milling had an integrated intensity that was about 30% that of the original MCC sample, matching with the cellulose concentration of the wood (about 30% to 40%). We normalized the integrated intensity of 2.79 THz to 3.32 THz into 1 to 0 by a min–max algorithm and proposed a new “index” for evaluating crystallinity.
Highlights
Cellulose is a macromolecular polysaccharide composed of glucose units, where the β (1 → 4)-D-glucose units are linked to a linear chain by hydrogen bonds (Updegraff 1969) and the cellulose chains further are linked to a sheet structure
We continuously explored the possibility of THz time-domain spectroscopy (THz-TDS) in cellulose research
After background subtraction and baseline correction, the corrected X-ray powder diffraction (XRD) patterns can be considered as composites of an amorphous intensity curve and five main crystalline peaks for the Iβ type cellulose, a dominant type in vascular plants such as wood
Summary
Cellulose is a macromolecular polysaccharide composed of glucose units, where the β (1 → 4)-D-glucose units are linked to a linear chain by hydrogen bonds (Updegraff 1969) and the cellulose chains further are linked to a sheet structure. The integrated intensity of the detrended spectra showed a correlation with the mass fraction of lignin of the pseudo-wood, and ball milling time of MCC and wood. Different from determination of the CrI of cellulose by deconvolution of the XRD pattern, 60 the processing of THz mass absorption coefficient spectra was relatively simple.
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