Phenol-assisted depolymerization of Acacia mangium tannin for strong and fast-curing biomass-based phenolic resins

Traditional phenolic resins have issues such as high petroleum consumption and high curing temperatures. This study is the first to use cost-effective phenol as a nucleophile to depolymerize Acacia mangium tannin (AMT) under acidic conditions at 60 °C. Matrix-Assisted Laser Desorption/ Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS) showed that the polymerization degree of the depolymerized Acacia mangium tannin (AMT-d) decreased from 9 to 2. Subsequently, depolymerized Acacia mangium tannin-phenol-formaldehyde resin (DT-PF) was prepared by replacing 50% of phenol with AMT-d. The thermal properties of the resins were tested using a Differential Scanning Calorimeter (DSC) and a Thermal Gravimetric Analyzer (TGA), and their bonding performance was analyzed via lap shear and plywood tests. The curing temperature of DT-PF was 145.7 °C, which is lower than that of phenol-formaldehyde resin (PF) (178.8 °C). Compared with Acacia mangium tannin-phenol-formaldehyde resin (T-PF), its residual rate, bonding strength, and debonding work (the total energy required for adhesive-substrate separation, calculated from the area under the load-displacement curve obtained during the lap shear test) increased by 12.3%, 32.6%, and 114.5%, respectively. After curing at 120 °C, its bonding strength was 0.9 MPa, exceeding that of PF (0.78 MPa) and T-PF (0.62 MPa). These results indicate that DT-PF, with a rapid curing rate, superior bonding performance, and high thermal stability, is a viable alternative to traditional phenol-formaldehyde resins.