Speaker
Description
Cellulose is an abundant renewable polymer with potential applications in sustainable packaging, coatings and functional composites. Its hydroxyl groups enable hydrogen bonding and chemical modification, providing opportunities to tailor its interactions with other components. Methylcellulose, a cellulose derivative obtained by partial methyl substitution, is also used as a film-forming material and polymer matrix. Comparing these materials offers an opportunity to examine how changes in chemical structure affect interactions with water. This is relevant because moisture can influence the structure and properties of cellulose-based materials. The present study aims to clarify the roles of methyl substitution and hydration in the vibrational response of cellulose and methylcellulose by combining Fourier-transform infrared (FTIR) spectroscopy with density functional theory (DFT) calculations. Experimental spectra of specimens with and without preliminary drying were recorded over 450–4000 cm⁻¹ using a Shimadzu IRTracer-100 spectrometer with an attenuated total reflection accessory. Complementary DFT calculations were performed at the B3LYP/6-31G level for cellulose and methylcellulose trimers, designated CL3 and MC3, with and without explicit water molecules. In MC3, methyl substitution at O2 and O6 provides a defined model for examining the effect of replacing hydroxyl hydrogens with methyl groups. The analysis considers O–H and C–H stretching vibrations, C–O and C–O–C vibrations, and the contribution of water. Particular attention is given to changes in band positions, relative intensities and profiles, as well as to the dependence of calculated vibrations on local hydrogen-bond arrangements. Atomic displacement vectors are examined alongside unscaled harmonic frequencies to distinguish polymer and water motions and identify their coupling. This combined approach is intended to help separate the spectral effects of chemical substitution from those associated with hydration and sample preparation. The study can provide a molecular basis for interpreting overlapping infrared bands and assessing the sensitivity of spectral features to water interactions. Such understanding could support the selection of drying and storage conditions for reproducible measurements and inform the development of cellulose-based films, coatings and functional composites whose performance depends on moisture. The calculations complement the experimental analysis by linking spectral features to local interactions between the polymer and water molecules.
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