Studies on microcapsules. II. Influence of molecular weight of ethylcellulose in the microencapsulation of ascorbic acid.

Microcapsules of ascorbic acid were prepared by phase separation of ethylcellulose (EC) from cyclohexane solution by lowering the temperature. The effects of molecular weight of EC on the aggregation of microcapsules and on the sustained release of the microencapsulated ascorbic acid were investigated. Polyisobutylene (PIB) was used as a coacervation-inducing agent. The molecular weight of EC significantly affected the aggregation of microcapsules ; the aggregation decreased with increasing molecular weight of EC. The release rate of ascorbic acid from microcapsules was influenced significantly by the molecular weight of EC and the minimum release rate was given by EC with a molecular weight of 13×104 if PIB with a molecular weight of 1.12×106 was used. The molecular weight of EC which gave minimum release rate was affected by the molecular weight of PIB used. The relationship between the release rate and molecular weight of EC depended mainly on the compactness of the wall rather than the thickness of the wall.