Novel Terahertz Spectroscopy Technology for Crystallinity and Crystal Structure Analysis of Cellulose

Area of Science:

• Materials Science
• Spectroscopy
• Biomaterials

Background:

• Crystallinity is crucial for assessing fiber material quality.
• Terahertz (THz) spectroscopy offers non-destructive analysis with excellent penetration and detection capabilities.
• THz technology shows significant potential for characterizing cellulose crystallinity.

Purpose of the Study:

• To investigate the application of terahertz spectroscopy for determining the crystallinity of different cellulose types.
• To compare THz-based crystallinity measurements with traditional methods like X-ray Diffraction (XRD) and Fourier-Transform Infrared (FT-IR) spectroscopy.
• To establish the relationship between THz absorption coefficients and cellulose crystallinity.

Main Methods:

• Terahertz spectroscopy was used to probe absorption peaks of wood cellulose (WC), microcrystalline cellulose (MCC), wood cellulose nanofiber (W-CNF), and cotton cellulose nanofiber (C-CNF).
• Crystallinity was calculated from THz spectra and compared with XRD and FT-IR results.
• Density functional theory (DFT) was employed to obtain cellulose molecular motion vibration models.

Main Results:

• The crystallinity of cellulose samples measured by THz spectroscopy were: WC (73%), MCC (78%), W-CNF (85%), and C-CNF (90%).
• Fiber lengths varied: WC (300 μm), MCC (20 μm), C-CNF (50 μm), and W-CNF (250 μm).
• THz absorption coefficients of cellulose were found to be proportional to the degree of crystallinity.

Conclusions:

• Terahertz spectroscopy is a viable technique for quantifying cellulose crystallinity.
• Optimal THz spectral analysis was achieved with a 1 mm sample thickness and a 1:1 polyethylene-to-cellulose ratio.
• Five distinct molecular motion models of cellulose correspond to five absorption peaks in the terahertz spectra.