Tailoring Acacia mangium Tannin Reactivity via Acid/Formaldehyde Treatment for High‐Performance Bio‐Based Phenolic Resins

ABSTRACT Traditional phenol–formaldehyde (PF) resins encounter a conflict between biomass substitution and cost reduction‐performance enhancement, limiting their application in wood structural materials. This study proposes an integrated strategy involving acid‐catalyzed treatment of tannin in the presence of formaldehyde, followed by in situ phenolic resin synthesis. Formaldehyde is introduced as an economical nucleophilic trapping agent to stabilize reactive intermediates generated under acidic conditions, leading to FD‐AMT with reduced molecular weight and improved reactivity. The low steric hindrance of FD‐AMT remarkably enhances compatibility with the matrix, resulting in resins termed FDT with strong hydrogen bonds and high‐density covalent bonds. The curing temperature of FDT 40 decreases to 124.8°C, which is 54.5°C lower than that of PF, while the gel time is reduced to 607 s. The wet bonding strength reaches 1.22 MPa, and the debonding work is 1.473 J, representing improvements of 35.5% and 145.5%, respectively, compared to TPF 40 . The wet bonding strength of FDT 60 remains at 0.89 MPa, satisfying the Class I plywood requirements. The FDT demonstrates good bonding compatibility across various wood substrates, with a strength retention rate of 92.6% after accelerated aging and a bonding strength of 2.61 MPa at −196°C. This strategy provides a novel approach for the high‐value utilization of biomaterials and the development of high‐performance biomass adhesives.