Poly(lactic acid) microcapsules: Tailoring properties via solid state polymerization

Abstract Active compounds encapsulation in polymeric carriers is a widely used technology as it protects and improves the physical characteristics of the active compound and controls its delivery. Polymeric microcapsules (MCs) effectiveness is strongly related to the barrier properties of the polymeric shell, which in turn are dependent on the shell molecular weight and crystallinity. Therefore, the aim of this study was to tailor these two MCs attributes via solid state polymerization (SSP) and to examine SSP efficiency as a post-encapsulation modification step. More specifically, double emulsion-solvent evaporation technique was efficiently applied to prepare unloaded PLA MCs of four different molecular weights which were then subjected to SSP in a fixed bed reactor under nitrogen flow. Post-polymerization reactions occurred in the shell of the microcapsules as evidenced by the increase of the molecular weight. In parallel, SSP on the MCs served as a post-crystallization step resulting in higher melting properties, i.e. melting temperature and crystallinity. Adapting the SSP process from the conventional bulk polymer scale to the microcapsule geometry scale was herein proved feasible to overcome any drawbacks of the conventional encapsulation stage and to produce customized application products.