Solid State Polymerization on Poly(Lactic Acid)‐Based Microcapsules: Process Parameters Adjustment in Order to Design Coumarin‐6 Encapsulation System

ABSTRACT Microencapsulation is a widely used technique for controlling the release of active compounds, protecting and/or improving their physical characteristics. Polymer molecular weight (MW) and thermal properties are associated with the effectiveness of the encapsulation system, as barrier properties change with the initial polymer. Recently, it was proved that Solid State Polymerization (SSP) can act as a post‐encapsulation modification tool on poly(lactic acid) microcapsules (MCs). This study aims to improve the SSP process, study its kinetics, and transfer the gained knowledge to loaded with coumarin‐6 microcapsules (LMCs). Herein, microcapsules (MCs) of two different molecular weight PLA grades (ca. 20,000 g/mol and ca. 45,000 g/mol) were prepared via double emulsion solvent evaporation technique. SSP process optimization involved screening of reaction temperature and pre‐crystallization conditions. Then, SSP was performed for different durations in a fixed bed reactor, reaching molecular weight and crystallinity increases of up to 40% and 70% respectively. Regarding SSP kinetics, low molecular‐weight MCs followed a power‐law model with reaction order ( n ) 0.328, while high‐molecular‐weight MCs data fitted best to an end‐group based expression for 2nd order kinetics. Transferring this gained knowledge to LMCs loaded with coumarin‐6, the untreated PLA shell permitted almost 64% of the encapsulated compound to be released within 15 days, while the SSP treatment retarded the release, reaching almost 44% for the same period of time.