A novel rosin-based non-isocyanate polyurethane with high-strength, self-healing, and recyclable properties for wood adhesives

Non-isocyanate polyurethane (NIPU) has received wide attention as a material prepared from renewable resources. Nevertheless, due to its poor mechanical properties, NIPU is difficult to replace conventional polyurethane to achieve large-scale production and practical applications. Hence, using rosin derivatives as raw materials, biogenic cyclic carbonic acid esters were synthesized by carbon dioxide (CO2) coupling reaction, and then cured with polyethylenimine (PEI) to form a new renewable NIPU thermosetting network without catalysts. The introduction of a rosin rigid structure and the formation of a hyperbranched structure make the obtained NIPU have excellent tensile strength (up to 40.50 MPa). Meanwhile, the hydrogenated phenanthrene ring structure of rosin restricts the movement of the NIPU chain, which leads to good thermal stability. Taking advantage of the transesterification of carbamates, the resultant NIPU exhibited self-healing, recyclability (recovery efficiency reached 89.50%), and shape memory. In addition, abundant polar groups endow NIPU with good adhesion strength. The innovative bio-based NIPU materials that are suggested in this work exhibit a variety of benefits, such as low curing temperature, outstanding mechanical properties, environment friendliness, and thermal stability, and have various applications in furniture and printing, adhesives, packaging materials, and other industries.