Sustained fragrance release from eugenol-loaded microcapsules via an in-situ formed viscous core

The high volatility of eugenol severely restricts its application in long-lasting fragrances. While microencapsulation is a common solution, conventional materials face significant limitations: melamine-formaldehyde (MF) microcapsules raise safety concerns, while monolithic polymer shells often undergo swelling and rupture, leading to premature leakage. Herein, we present a novel and safe microencapsulation platform based on an in-situ core viscosification strategy. We designed double-shelled microcapsules featuring an inner sacrificial shell of poly (styrene-acrylic acid) and an outer rigid shell of cross-linked polystyrene. The pivotal innovation lies in the post-encapsulation dissolution of the inner shell by eugenol, which transforms the liquid core into a highly viscous, polymer-rich matrix. This transformation intrinsically retards fragrance diffusion, without compromising the initial capsule formation. Systematic optimization of fabrication parameters yielded microcapsules with exceptional mechanical strength, exhibiting a rupture force of 7.24 ± 0.39 mN and toughness of 2.42 ± 0.24 J/m 3 . Release kinetics and thermal analysis demonstrated a profound enhancement in sustained release, with exhibited remarkably sustained release behavior compared to conventional MF microcapsules, and a major release event shifted to a temperature over 100 °C higher. This work presents an in-situ core viscosification strategy driven by synergistic sacrificial-layer dissolution and molecular entanglement for sustained fragrance delivery, offering a high-performance, formaldehyde-free alternative for cosmetics and textiles.