Innovative design and green synthesis of bio-based non-isocyanate polyurethanes: Efficient combination of cardanol and carbon dioxide with high fire safety and robust adhesion

Under the background of fossil fuel depletion and global warming, the large amount of carbon dioxide (CO2) produced by industrial production was a renewable, clean and natural C1 feedstock that was becoming an ideal feedstock to produce value-added chemicals. The synthesis of non-isocyanate polyurethanes (NIPU) from cyclic carbonates as intermediate products was a typical way to realize the efficient recycling of CO2. To improve the low carbonization, flammability and poor mechanics of NIPU and expand its application scenarios, the NIPU was synthesized from biological cardanol and CO2 by a relatively green synthesis route, and modified by flame retardants containing different valence phosphorus. Compared with ECH-CarCO2-HMDA, the char residue of PO-CarCO2-HMDA and PP-CarCO2-HMDA increased by 248.8 % and 172.7 % respectively under nitrogen atmosphere, and 345.7 % and 151.9 % respectively under air atmosphere. More importantly, the peaks of heat release rate of modified NIPUs were reduced by 30.0 % and 18.4 %, and their total heat release were decreased by 15.2 % and 10.4 %, respectively. After various characterization analysis, this was mainly due to the generation of heat-stable structure containing phosphorus and oxygen during the burning process. Simultaneously, the toughness of PO-CarCO2-HMDA and PP-CarCO2-HMDA increased by 261.0 % and 105.1 %. In addition, the synthetic NIPU as an adhesive in different materials was also explored, and the adhesion strength can reach 2.47 MPa. This study provided a new idea for preparing bio-based NIPU which was more widely used.