Broadband terahertz spectroscopy of cellulose nanofiber-reinforced polypropylenes

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.