Bio‐Based Epoxy–Ester Vitrimers Reinforced With Rice‐Straw Lignin: From Network Design to Corrosion‐Protective Coatings and Thermally Rebondable Structural Adhesives

ABSTRACT

This study examines bio‐based epoxy–ester vitrimer networks prepared from epoxidized soybean oil (ESO), divanillic acid (DVA), and rice‐straw lignin obtained by ultrasound‐assisted alkaline treatment. The COOH/epoxy ratio (0.7–1.5) and lignin loading (0–30 wt%) were varied to relate formulation, exchange dynamics, coating performance, and adhesive reusability. For ESO–DVA–1.0–L20, the coating showed a pull‐off adhesion of 9.69 ± 0.12 MPa, 182 ± 18 MEK double rubs, and a minimum mandrel diameter of 4.43 ± 0.71 mm. After 30 days in 3.5 wt% NaCl, | Z | at 0.01 Hz was approximately 1.0 × 10 ⁹  Ω cm ² , compared with approximately 8.2 × 10 ⁸  Ω cm ² for the lignin‐free analogue. Thermal treatment at 200°C for 1 h increased | Z | at 0.01 Hz from approximately 2.5 × 10 ⁷ to 2.0 × 10 ⁸  Ω cm ² , corresponding to approximately 13% of the intact‐coating value (approximately 1.5 × 10 ⁹  Ω cm ² ). Optical microscopy, SEM, and 3D profilometry further showed reductions of 37.5% in scratch width and 44.4% in scratch depth, confirming partial rather than complete damage recovery. The same formulation reached an initial lap‐shear strength of approximately 14.7 MPa and retained approximately 89% after three rebonding cycles; its Mode‐I fracture energy was approximately 1.36–1.56 kJ m ⁻² .