Sodium Alginate-Encapsulated Oregano Essential Oil Microcapsules for the Conservation of Waterlogged Archaeological Wood

Waterlogged archaeological wood is highly vulnerable to degradation by wood-degrading microorganisms. Oregano essential oil (OEO) shows excellent antimicrobial activity against such microbes, but its high volatility and poor stability restrict direct application in cultural relic protection. This study aims to optimize the preparation of sodium alginate (SA)-based OEO microcapsules (OEO@SAM), characterize their structural and physicochemical properties, and evaluate their sustained-release antimicrobial performance for waterlogged archaeological wood conservation. OEO@SAM was fabricated via ionic crosslinking, with orthogonal experiments optimizing three key parameters: OEO:SA ratio, SA concentration, and CaCl₂ concentration. The microcapsules were characterized by morphological observation, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), etc. Encapsulation efficiency (EE), in vitro sustained-release kinetics, and antimicrobial activity against dominant wood-degrading microorganisms (isolated from waterlogged archaeological sites) were tested. The OEO:SA ratio was the dominant factor regulating EE: EE decreased sharply as the OEO:SA ratio increased, with the highest EE (24.05%) achieved at OEO:SA = 0.5, SA = 2%, and CaCl₂ = 3%. Meanwhile, only 0.71 g/L of OEO@SAM is required to inhibit bacterial growth and achieve the conservation of waterlogged archaeological wood. OEO@SAM exhibited stable sustained release (fitting the zero-order kinetic model) and significant antimicrobial activity against target microorganisms. It provides a new type of antibacterial and antifungal material for the in situ conservation of waterlogged archaeological wood.