Tung Oil‐Loaded PU / SiO 2 Hybrid Microcapsules With Enhanced Apparent Stiffness: Improving Mechanical Reinforcement and Anticorrosion Performance in Self‐Healing Epoxy Coatings

ABSTRACT Microcapsules are widely used in self‐healing coatings, yet the mechanical contribution of the microcapsule shell to coating performance remains insufficiently understood. In this article, tung oil‐loaded polyurethane/silica hybrid microcapsules (TO@PU/SiO 2 ) were prepared by Pickering emulsion templating and compared with polyurethane microcapsules (TO@PU) to investigate the effect of capsule apparent stiffness on the mechanical and functional properties of epoxy coatings. The incorporation of surface‐modified SiO 2 nanoparticles into the polyurethane shell produced organic–inorganic hybrid microcapsules with enhanced resistance to localized deformation. The apparent Young's modulus of intact liquid‐filled TO@PU/SiO 2 microcapsules reached 1.23 ± 0.16 GPa, approximately 4.4 times higher than that of TO@PU microcapsules (0.28 ± 0.02 GPa). At an optimized loading of 5 wt.%, the TO@PU/SiO 2 (5)‐EP coating exhibited an increased tensile strength of 3.18 ± 0.11 MPa while maintaining favorable adhesion and Shore D hardness. Furthermore, its low‐frequency impedance modulus remained above 10 7 Ω·cm 2 after 21 days of immersion in 3.5 wt.% NaCl solution. After scratching, tung oil released from the ruptured microcapsules progressively sealed the damaged region, achieving a self‐healing efficiency of 39.73% within 24 h. These results demonstrate that enhancing microcapsule apparent stiffness through SiO 2 reinforcement contributes to improved coating mechanical integrity while maintaining effective corrosion protection and damage‐triggered self‐healing capability. This work highlights the dual function of stiffness‐enhanced microcapsules as mechanical reinforcing components and healing‐agent reservoirs, providing a strategy for designing mechanically robust self‐healing anticorrosion coatings.