Crystalline structure analysis of cellulose treated with sodium hydroxide and carbon dioxide by means of X-ray diffraction and FTIR spectroscopy Original Research Article

Crystalline structures of cellulose (named as Cell 1), NaOH-treated cellulose (Cell 2), and subsequent CO2-treated cellulose (Cell 2-C) were analyzed by wide-angle X-ray diffraction and FTIR spectroscopy. Transformation from cellulose I to cellulose II was observed by X-ray diffraction for Cell 2 treated with 15–20 wt % NaOH. Subsequent treatment with CO2 also transformed the Cell 2-C treated with 5–10 wt % NaOH. Many of the FTIR bands including 2901, 1431, 1282, 1236, 1202, 1165, 1032, and 897 cm−1 were shifted to higher wave number (by 2–13 cm−1). However, the bands at 3352, 1373, and 983 cm−1 were shifted to lower wave number (by 3–95 cm−1). In contrast to the bands at 1337, 1114, and 1058 cm−1, the absorbances measured at 1263, 993, 897, and 668 cm−1 were increased. The FTIR spectra of hydrogen-bonded OH stretching vibrations at around 3352 cm−1 were resolved into three bands for cellulose I and four bands for cellulose II, assuming that all the vibration modes follow Gaussian distribution. The bands of 1 (3518 cm−1), 2 (3349 cm−1), and 3 (3195 cm−1) were related to the sum of valence vibration of an H-bonded OH group and an intramolecular hydrogen bond of 2-OH⋯O-6, intramolecular hydrogen bond of 3-OH⋯O-5 and the intermolecular hydrogen bond of 6-O⋯HO-3′, respectively. Compared with the bands of cellulose I, a new band of 4 (3115 cm−1) related to intermolecular hydrogen bond of 2-OH⋯O-2′ and/or intermolecular hydrogen bond of 6-OH⋯O-2′ in cellulose II appeared.