Green synthesis of lignin-based non-isocyanate polyurethanes as reusable, self-healable and removable adhesives

Lignin-based non-isocyanate polyurethanes (LNIPUs) represent a class of polymers synthesized from lignin-an abundant, renewable polymer found in the cell walls of plants-without the use of toxic isocyanates. This makes LNIPUs an eco-friendly alternative to traditional petroleum-based polyurethanes. Despite their advantages, the synthesis of LNIPUs often entails complex processes, the use of additional catalysts, and highly polar solvents, which largely restrict their accessibility and practical applications. In this study, we present an higly efficient, catalyst-free, and solvent-free methodology for synthesizing LNIPUs. A series of novel LNIPUs were successfully prepared through a one-pot, catalyst-free and solvent-free polymerization reaction involving aminated fractionated lignin (ALF(E)) and bis(6-membered cyclic carbonate) (6CC). We systematically investigated the properties of the resulting LNIPUs, with a particular focus on the adhesion performance. The incorporation of ALF(E) significantly enhanced the adhesive properties of the resultant LNIPUs on aluminum, wood, and plastic substrates, achieving a maximum bonding strength of 3.09 MPa on aluminum. Furthermore, LNIPUs exhibit exceptional functionalities, including reusability, self-healing capabilities, and removability, along with improved thermal stability and photothermal properties.