title: A study on water adsorption onto microcrystalline cellulose by near-infrared spectroscopy with two-dimensional correlation spectroscopy and principal component analysis.
abstract: Water adsorption onto microcrystalline cellulose (MCC) in the moisture content (M(c)) range of 0.2-13.4 wt % was investigated by near-infrared (NIR) spectroscopy. In order to distinguish heavily overlapping O-H stretching bands in the NIR region due to MCC and water, principal component analysis (PCA) and generalized two-dimensional correlation spectroscopy (2DCOS) were applied to the obtained spectra. The NIR spectra in four adsorption stages separated by PCA were analyzed by 2DCOS. For the low M(c) range of 0.2-3.1 wt %, a decrease in the free or weakly hydrogen-bonded (H-bonded) MCC OH band, increases in the H-bonded MCC OH bands, and increases in the adsorbed water OH bands are observed. These results suggest that the inter- and intrachain H-bonds of MCC are formed by monomeric water molecule adsorption. In the M(c) range of 3.8-7.1 wt %, spectral changes in the NIR spectra reveal that the aggregation of water molecules starts at the surface of MCC. For the high M(c) range of 8.1-13.4 wt %, the NIR results suggest that the formation of bulk water occurs. It is revealed from the present study that approximately 3-7 wt % of adsorbed water is responsible for the stabilization of the H-bond network in MCC at the cellulose-water surface.
authors.affiliation: Department of Chemistry and Research Center for Near Infrared Spectroscopy, School of Science and Technology, Kwansei-Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Watanabe
authors.forename: Shigeaki
authors.initials: S
authors.lastname: Morita
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Ozaki
mesh_terms: D000327:Adsorption; D002482:Cellulose / Q000737:chemistry*; D006860:Hydrogen Bonding; D025341:Principal Component Analysis; D019265:Spectroscopy, Near-Infrared; D013057:Spectrum Analysis; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D002482:Cellulose; C109691:microcrystalline cellulose