Drying process of sodium alginate films studied by two-dimensional correlation ATR-FTIR spectroscopy

•Existence of free and hydrogen-bonded COO− groups were detected by 2DCOS.•O2 and O3 of the pyranose ring might have preferentially formed hydrogen bond.•Water molecules were more sensitive than alginate molecules during drying.•Sequence of spectral changes during the drying process was studied by 2DCOS. Drying process of aqueous sodium alginate solutions at 50°C was investigated by ATR-FTIR spectroscopy and two-dimensional correlation infrared spectroscopy. Two-dimensional asynchronous spectrum at 1800–1350cm−1 wavenumber could be resolved into five separate bands, which were assigned to O–H bending vibrations in water (around 1645cm−1), antisymmetric and symmetric stretching vibrations of free and hydrogen-bonded COO− groups of alginate (around 1595, 1412, 1572 and 1390cm−1, respectively). As the drying process progressed, absorbance bands at around 1127 and 1035cm−1 significantly shifted to lower wavenumbers (1120 and 1027cm−1, respectively). Suggesting that oxygen atoms at the 2th and 3th position in the pyranose ring might have hydrogen bonded with water or alginate chains. Further analysis using 2D asynchronous correlation spectroscopy between 1800–1500 and 1200–960cm−1 wavenumber regions revealed the sequence of spectral changes during the drying process.