Preparation of Multifunctional Alginate–PEG–Chitosan Double Shell and Thyme Oil–Oleic Acid Core Microcapsules via Coaxial Electrospraying

The growing interest in bio-based and bioactive materials, as well as sustainable production techniques, has driven the development of multifunctional hybrid systems. This study reports the fabrication of novel microcapsules with a double-layer alginate–PEG–chitosan shell, with or without a core, via coaxial electrospraying, followed by ionotropic gelation and polyelectrolyte complexation. PEG1000 and PEG1500 were incorporated into the shell as phase change materials, and thyme oil–oleic acid served as a hydrophobic bioactive core. Scanning electron microscopy and Fourier transform infrared analyses confirmed the structural integrity and effective shell–core integration. Thermogravimetric analyses showed enhanced thermal stability in double-layer alginate–PEG–chitosan biopolymer network shell and thyme oil included core system, with a delayed degradation up to 370.0 °C and reduced mass loss compared to the alginate–chitosan control sample. Differential scanning calorimetry over ten heating–cooling cycles demonstrated significant phase transition enthalpies (70.5–91.8 J·g−1 at 37.6–48.5 °C), confirming efficient thermal energy storage and release governed by the PEG content. Aqueous suspensions prepared from microcapsules exhibited reversible temperature-dependent swelling–deswelling behavior between 20.0 and 55.0 °C, governed by hydrogel properties of the alginate–chitosan shell interactions. The microcapsules exhibited pronounced pH-dependent swelling (enhanced at pH 7.0), high water solubility, and good antioxidant activity. These findings highlight the broad application potential of bio-based shell–core microcapsules, e.g., active food packaging, biomedical dressings, protective coatings, pharmaceutical and biomedical delivery systems and functional textiles.