A Fully Biobased Benzoxazine-Modified Waterborne Two-Component Polyurethane with High Adhesion, Self-Healing, and Hydrophobic Properties

To address the limitations of traditional waterborne two-component polyurethane (2k-WPU) in terms of water resistance, mechanical strength, and adhesion, this study developed an all-biobased composite material (WPU-VF) using a dual covalent cross-linking strategy. A lignin-derived benzoxazine monomer (VF) was synthesized from vanillic acid and furfurylamine and introduced into 2k -WPU to form a rigid aromatic network through ring-opening polymerization. This improved the material’s mechanical properties (tensile strength: 28 MPa), hydrophobicity (contact angle: 101°), and wet adhesion (only a 13% loss of shear strength after soaking). The material also exhibited rapid self-healing ability (10 min at 140 °C), triple shape memory performance, and recyclability (92.8% strength retention after two cycles). Notably, WPU-VF-0.3 completely degraded within 2 h under mild alkaline conditions, complying with the principles of the circular economy. The waterborne process minimized the emission of volatile organic compounds (VOCs). This sustainable design provides a high-performance, recyclable, and degradable polymer solution, which is expected to be applied in the fields of environmentally friendly coatings, food packaging materials, and smart adhesives, reducing dependence on petrochemical products and waste accumulation.