Formation of shellac succinate having improved enteric film properties through dry media reaction

The aim of this study was to improve enteric properties of shellac by the formation of succinate derivative through dry media reaction. Shellac and succinic anhydride were mixed and then co-ground by planetary ball mill. The ground mixture was then activated by heating for various times and washed for removal of excess succinic anhydride. The ground mixtures and the heat-activated mixtures were characterized by physical and chemical tests, including acid value, FTIR spectroscopy, 1H NMR and 13C NMR spectroscopy, thermal analysis and film properties. The results demonstrated that acid values of heat-activated shellac mixtures increased with the increase of annealing time, suggesting the presence of carboxylic acid moieties of succinate at shellac molecules. The results were in good agreement with the DSC thermograms. The melting peak of shellac disappeared after heating, while melting peak of succinic anhydride gradually decreased, suggesting the utilization of succinic anhydride for the esterification. The shellac succinate formation was also confirmed by 1H NMR and 13C NMR spectroscopies. Film prepared from shellac succinate showed improved solubility, especially at the pH of small intestine (5.8–6.7), as compared to native shellac. The shellac succinate film also demonstrated better mechanical property, in terms of increased flexibility. In conclusion, solid-state formation of shellac succinate ester, which had improved enteric properties, was easily accomplished under the concept of “green approach”.