The Raman spectroscopy approach to the study of Water–Polymer interactions in hydrated hydroxypropyl cellulose (HPC)

Abstract

Raman spectroscopy was used to investigate molecular interactions and the water binding structure in hydrated hydroxypropyl cellulose Klucel® Pharm HPC type MF. During the study, there were examined samples with water content equal to 0.69, 1.41 and 2.17 g/g. In this case, the water concentration was defined as the ratio of the mass of water to the mass of the dry polymer. The first content was close to the previously determined amount of non-freezing water that was found to be 0.54 g/g (calorimetric studies). The analysis was focused on the O–H stretching band region range from 3600 to 3000 cm−1. The received 3 bands at ca. 3400 cm−1, 3320 cm−1 and 3220 cm−1 were assigned to non-freezing water, freezing bound water and free water respectively. Changes in the 1235-1000 cm−1 glycosidic linkage range were also analyzed as well as in the 3000-2850 cm−1 range of C–H stretching vibrations of the CH2 and CH3 groups. Changes in the asymmetrical CH stretching vibrations of the methylene and symmetrical CH stretching vibrations of CH3 were also discussed.