Temperature-Dependent Structural Changes in Hydrogen Bonds in Microcrystalline Cellulose Studied by Infrared and Near-Infrared Spectroscopy with Perturbation-Correlation Moving-Window Two-Dimensional Correlation Analysis

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Abstract
Temperature-dependent structural changes in hydrogen bonds (H-bonds) in microcrystalline cellulose (MCC) were investigated by infrared (IR) and near-infrared (NIR) spectroscopy. The O–H stretching fundamentals and their first overtone bands were employed to explore the structural changes. In order to analyze the overlapping OH bands due to various H-bonds, perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy was applied to the IR and NIR data. Typical spectral variation temperatures were visualized by the PCMW2D correlation analysis. Structural changes in the strong H-bonds in MCC gradually occur in the temperature region of 25–130 °C, and they become greater above 130 °C. Both OH groups with H-bonds of intermediate strength and very weak H-bonds arise from the structural change of strong H-bonds in the temperature region of 40–90 °C, whereas the appearance of the latter OH groups with very weak H-bonds gradually becomes dominant above 90 °C. It is revealed from the present study that the glass transition at 184 °C induces the changes in the H-bonds in the Iβ and the O3–H3…O5 intrachain H-bonds. Band assignments for the O–H stretching first overtone vibration region are proposed based on the results of the PCMW2D correlation analyses.

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