Synthesis and Characterisation of Aminoplast Microcapsules for Controlled Release of Bioactives. Influence of the Resin:Oil Ratio

In this study a series of melamine-formaldehyde (MF) microcapsules containing Melaleuca alternifolia oil as natural biocide with different polymer to oil ratio was prepared by the in situ polymerization (O/W) method. The characterization of the microcapsules properties was undertaken by different experimental techniques in order to establish a correlation between the polymer to oil ratio and the oil encapsulation efficiency and properties for further applications. The average size distribution was determined by Laser Diffraction Scattering (DLS) and the chemical structure by Fourier Transformed Infrared Spectroscopy (FTIR). The morphology was characterized by Scanning Electron Microscopy (SEM). Finally, the thermal stability of microcapsules and the permeability of the shell to the diffusion of the core material were analyzed by Thermogravimetric Analysis (TGA). The obtained results showed that the resin:oil ratio was critical in the microcapsule formation and properties. For lower values than the critical one there was no microcapsule formation. For values over the critical resin:oil ratio value microcapsules were formed with spherical morphologies of varying wall thickness and oil encapsulation.