FTIR spectroscopy is an appropriate technique to evaluate the changes in the chemical compositions of the samples in response to native cellulose and yielded nanocellulose (CNCH2SO4 and CNCCr(NO3)3). As presented in Figure 3, the FTIR spectra of all the samples exhibited two major absorbance regions, which included the high (3500–2800 cm−1) and low wavenumbers (1700–500 cm−1) regions, consistent with previous studies . A broad and dominant absorbance peak located in the region of 3600 to 3200 cm−1 was observed in all spectra, which corresponded to the characteristic of hydrogen bonding O–H stretching vibrations . In addition, C–H stretching gave rise to the band at 2900 cm−1 . A small peak was detected at 1640 cm−1 associated with –OH bending vibration of absorbed water by the fibers as the cellulose is hygroscopic in nature , whereas the peak at 1430 cm−1 related to the intermolecular hydrogen attraction at the C6 group . Although all the samples were subjected to a proper drying process prior to FTIR analysis, the complete elimination of moisture in the samples was very difficult due to the strong cellulose–water interaction . Moreover, the stretching vibration of the C–O–C pyranose ring within the cellulose molecules was observed at a sharp peak of 1054 cm−1 . Besides that, the fingerprint region of the FTIR spectra, which lies in the range within 600 to 1100 cm−1, is a significant signal for tracking the presence of β-glycosidic linkages that contributed by the vibration of wagging, deformation and twisting modes of the anhydro-glucopyranose units . Furthermore, the absence of NO3− peaks at 1384 cm−1 in the spectra implied the complete removal of Cr3+ metal salt during the washing by centrifuge and dialysis process .