Improvement of Bleached Shellac as Enteric Coating by Composite Formation.

The objective of this study was to stabilize the enteric property of bleached shellac by composite formation with ethyl cellulose. The composite film at the ratio of 9:1, 8:2, 7:3, 6:4, and 5:5 was prepared by the film casting method. The physicochemical properties were acid value, insoluble solid, water permeability coefficient, % polarity, mechanical property, FTIR, PXRD, DSC, % solubility in aqueous, and various pH (1.2 and 7.4). All the films were able to protect against the low pH and water. The total solubility at pH 7.4 was reported for the low ratio of ethyl cellulose (9:1 and 8:2). The stability of all films was then investigated for 180 days. The results demonstrated that the ethyl cellulose could stabilize the bleached shellac indicated by the low changes in acid value and insoluble solid. The higher ratio of ethyl cellulose contributed to the lower polymerization during storage. The results were due to the protection of the bleached shellac's active sites. The entanglement of ethyl cellulose caused interaction difficulties between active groups leading to stabilized bleached shellac. The proper ratio was 7:3 because of high solubility, and low polymerization. The findings demonstrated that the composite film could improve the enteric property of bleached shellac for a long period.