Solvent-free synthesis of bio-based non-isocyanate polyurethane (NIPU) with robust adhesive property and resistance to low temperature

Non-isocyanate polyurethane (NIPU) adhesives represent a cutting-edge advancement in adhesive technology, poised to significantly diminish the dependency on isocyanate-based PU within the industry. In the context of the increasing scarcity of petroleum-based resources and the growing imperative for sustainable environmental practices, the pursuit of a comprehensively sustainable, bio-derived non-isocyanate polyurethane (NIPU) adhesive has swiftly become a pivotal area of interest within the scientific research community. In this study, the cashew phenol cyclic carbonate (CPCC) was synthesized through the addition polymerization process involving cashew phenol glycidyl ether (602A) with carbon dioxide (CO₂), followed by a curing step utilizing a diamine extracted from biomass-derived oils to produce bio-based NIPU at ambient temperature. The synthesized NIPU adhesive demonstrated remarkable thermal stability and exceptional adhesion to a variety of substrate materials. Notably, the adhesive showcased superior bonding efficacy at ultra-low temperatures, with steel bonding strength reaching up to 7.78 MPa at -37°C. This study presents an efficient and accelerated synthesis approach for the preparation of bio-based NIPU, offering a significant contribution to the field. Moreover, it provides a valuable reference for future advancements in NIPU adhesive technology, particularly for applications requiring robust bonding at low-temperature environments.