Analytical Study of Irradiated Cellulose Derivatives

The aim of this study was to investigate the effects of ionizing radiation on the physicochemical properties of four excipients used in pharmaceutical technology (microcrystalline cellulose, methylcellulose, hydroxyethylcellulose and hydroxypropyl methylcellulose) with the view of using ionizing radiation for their sterilization. A number of analytical methods (FT-IR, XRD, TG,CPMAS NMR and measurements of pH and viscosity) were used to determine the radiostability of cellulose derivatives to ionizing radiation. The odour, form, microscopic presentation and water content determined by the Karl Fischer method of cellulose derivatives did not change after irradiation up to 200 kGy. There was a small difference (+/- 0.1 to 2 °C) between irradiated and non-irradiated samples for the decomposition temperature determined via DTG/TG method and for relaxation times determined by the CPMAS NMR. Significant changes were observed however in the colour and the pH of aqueous solutions (or suspensions). The viscosity was reduced as a result of irradiation and thixotropic properties disappeared. In the FT-IR spectra, a new peak was observed at ca 1730 cm-1 indicating the presence of either carbonyl or carboxylic groups. It was concluded that radiosterilization method as a way of decontamination of cellulose derivatives should not be used in doses exceeding 25 kGy because ionizing radiation may lead to changes in physicochemical properties and to the formation of radiolysis products.