Impregnation modification of wood with Flos Sophorae Immaturus flavonoid extract and metal ions: structure, physical properties, and antibacterial performance

Developing environmentally friendly and effective wood preservatives is crucial for extending the service life of wood and promoting sustainable resource utilization. In this study, flavonoids were extracted from Flos sophorae immaturus using deep eutectic solvent (DES), and the Flos Sophorae Immaturus flavonoid extract (SFE) combined with metal ions (Zn²⁺, Mg²⁺, Cu²⁺, Fe³⁺) and polyvinyl alcohol (PVA) as a carrier was used to modify Pinus sylvestris wood sequentially via vacuum impregnation. The results showed that the SFE and metal ion-PVA composites effectively penetrated and were stabilized within the wood structure. The treatment significantly improved the dimensional stability of the wood. Compared to untreated wood, the tangential, radial, and volumetric shrinkage were reduced by up to 74%, 60%, and 73%, respectively. Density increased, hardness was higher, hydrophilicity decreased, and the contact angle of the wood increased from 24.90° to 97.39° with the addition of PVA as well as different metal ionized PVA. The treated wood also had strong 60-day antibacterial activity against Staphylococcus aureus, Escherichia coli, and good antifungal performance against white rot fungi. Overall, this study presents a promising and eco-friendly approach using an SFE-metal ion-PVA system to enhance the durability and functional versatility of wood materials.