Release model of alginate microcapsules containing volatile tea-tree oil

We have prepared alginate calcium microcapsules containing tea tree oil and measured the release behavior. The release rate observed at different temperatures was almost constant with time. The data were analyzed by a theory for a model system consisting of encapsulated coexisting liquid and vapor phases. The theory predicts a polynomial-type release which is much more uniform than the exponential-type release appearing in conventional microcapsule systems and regarded as roughly constant release. The observed release curves were expressed well by the theoretical equation for the release, which supports the validity of the theory. From the fitting of the data to the theory, the time constant for vaporization in the core and that for permeation through the microcapsule membrane were determined. The activation energy for permeation through the membrane determined from the fitting parameters is much larger than that for vaporization.