Broadband terahertz spectroscopy of cellulose nanofiber-reinforced polypropylenes

Highlights: • CNF-reinforced PPs were investigated by Fourier transform THz spectroscopy. • A new peak at 7.0 THz appeared when CNF was added, while PP peaks remained unchanged. • The 7.0 THz peak was attributed to the intermolecular vibration mode in CNF. • CNF content in PPs cannot be determined using conventional XRD technique. • Broadband THz spectroscopy is a powerful tool for CNF-containing nanocomposite polymers. Cellulose nanofiber (CNF)-reinforced polypropylenes (PPs) with different CNF content were investigated by Fourier transform terahertz (THz) spectroscopy over the frequency range of 1–10 THz. Absorption peaks of pure PP were identified at 3.1, 5.1, 7.5, and 9.6 THz, which indicate the isotactic structure is formed. A new peak at 7.0 THz appeared when CNF was added, while the PP peaks remained unchanged. Conventional X-ray diffraction (XRD) spectroscopy was also performed for comparison. The XRD results do not allow to determine the effect of CNF content in the properties of the composite. In contrast THz spectroscopy effectively showed the relationship between CNF content and the mechanical properties of the samples. The 7.0 THz can be used as an indicator for the nondestructive and noninvasive analysis of CNF-PPs.