Modelling of essential oils kinetics release from encapsulation matrix

Essential oils (EO) contain active agents (AA) possessing repellent, antimicrobial and insecticidal properties. Encapsulation is a way to control their release and increasing the AA activity. The release kinetic from the matrix in a controlled environment can be interpolated by the solution of a zero-, half- or first-order differential equation. Even if in practical the release rate might be more complicated, their parameters provide pertinent information about the processes. Several models exist to fit the experimental data and also to describe the release mechanisms such as Avrami, Korsmeyer-Peppas or Higuchi. In the field of controlled release, the Avrami’s equation was generally used to describe the dissolution of a drug in a liquid. Indeed, Avrami’s equation considers several phenomena that may occur simultaneous such as the diffusion of the penetrant into the matrix, the potential swelling of matrix and the release of drug. The objective of this study was to use these three different models to evaluate the release in atmosphere of two different essential oils from an organic matrix. The two essential oils: spearmint and sweet orange, are characterised by varied properties, the former being less volatile, more polar and more viscous than the latter. Moreover, limonene was present in both oils but in higher concentration in one of them. As expected, Avrami’s model leads to the best fit of the experimental kinetic data. The identification of the exponent of Avrami’s model: n, varying between 0.40 and 0.75, indicates that the prevailing release mechanism is diffusional for both essential oils. The usefulness and relevance of the other models will be discussed taking into account the essential oil nature and the envisaged practical applications.