Studies on Microcapsules. III. Influence of Molecular Weight of Polyisobutylene in the Microencapsulation of Ascorbic Acid

Abstract

The effect of molecular weight (M^^-) of polyisolbutylene (PIB), used as a coacervation-inducing agent in the preparation of ethylcellulose (EC) microcapsules (MC) in cyclohexane, was studied with ascorbic acid as the core material. PIBs of various M^^- were obtained by the fractionation of commercially available PIB and microencapsulation was performed. It was found that aggregation of MC decreased with increasing M^^- and was almost wholly prevented at M^^- of above 6×10⁵ and that the release rate of ascorbic acid became minimum at M^^- of around 2×10⁵. The effect of mixing of commercially available high M^^-PIB (9.5×10⁵) and low M^^-PIB (3×10⁴) on microencapsulation was also investigated. In this case the release rate became minimum at a mixing ratio of around 1 : 4 (high M^^- : low M^^-). With increase of low M^^-PIB, average wall thickness and compactness increased and the wall became less uniform. Thus, it was presumed that the most prolonged MC was produced when the compactness, thickness and uniformity of the wall were well balanced. The influence of M^^- of PIB on the coacervation process was also investigated by measuring the volume fraction, EC contents and viscosity of the coacervate phase. From these data, it was presumed that M^^- of PIB affects the properties of the coacervation droplet, and consequently influences the properties of the wall formed from the droplet.