Temperature effect on water desorption from methylcellulose films studied by thermal FT-IR microspectroscopy

Abstract

Temperature-induced desorption behavior of water from methylcellulose (MC) film was investigated by a novel microscopic Fourier transform infrared (FT-IR) spectroscopy equipped with thermal analyzer (thermal FT-IR microscopic system) and thermogravimetric analysis (TGA). The result indicates that the weight loss of water from MC film was markedly correlated to the IR spectral changes of OH stretching (3000–3800 cm −1) and bending (1649 cm −1) modes of water molecules. The shift of OH stretching mode from 3461 to 3481 cm −1 was accompanied with the water loss from MC film induced by temperature effect. Two stages of water desorption from MC film were proposed: the first stage within the 35–65 °C had a dramatic IR peak shift from 3461 to 3477 cm −1 and accompanied with a largest weight loss of water from MC film, which might be mainly due to the desorption of free water with minor weakly hydrogen-bonded water; the second stage beyond 65 °C would be desorption of moderately hydrogen-bonded bound water, due to the gradual IR spectral shift from 3477 to 3481 cm −1 and a slower weight loss of water from MC film. The changes in peak area ratio of 1649 cm −1/1374 cm −1 with the temperature also confirmed the IR spectral peak shift of the OH stretching mode via the water loss from MC film. The temperature-dependent dissociation of intermolecular and intramolecular hydrogen bonds within water molecules and/or between water/MC interaction might be responsible for the desorption kinetics of water from MC film.