Biobased self healing waterborne polyurethane with vanillin derived dynamic Imine bonds for enhanced mechanical strength and performance

Rising global interest in environmentally friendly, high-performance polymeric materials has accelerated the innovation of next-generation polyurethane systems. This research introduces a novel bio-based waterborne polyurethane, synthesized with a vanillin-derived green polyol chain extender featuring dynamic imine linkages. Vanillin diol (VAN-OH) was synthesized using a straightforward one-step condensation of vanillin and ethylenediamine, incorporating dynamic Schiff base functionality into the compound. The waterborne polyurethane (WPU) formulation was synthesized by combining the chain extender VAN-OH, dimethylolpropionic acid (DMPA), polytetrahydrofuran (PTHF), and isophorone diisocyanate (IPDI) in the proper molar ratios. The synthesis parameters were improved through a Design of Experiments (DoE) methodology to enhance mechanical characteristics. The WPU incorporating a vanillin-derived diol chain extender (WPU-VAN-OH) films exhibited a tensile strength of 12.8 MPa, three times greater than that of standard WPU at 4.3 MPa, and showed exceptional self-healing capabilities, completely mending surface scratches within 30 min at 80 °C by dynamic imine bond exchange. The material exhibited higher thermal stability, less water absorption (22.8% compared to 32.2% for WPU after 7 days), and superior adhesion to stainless steel (18.17 kgf/cm² versus 8.23 kgf/cm² for WPU). WPU-VAN-OH films presents a sustainable and efficient methodology for formulating polyurethanes characterized by high strength, self-healing properties, and environmental compatibility, appropriate for uses including protective coatings, advanced adhesives, and flexible elastomers.