Compatibility mechanism and fracture behavior of recycling polyurethane foam as asphalt extender: a molecular scale interpretation

A substantial proportion of waste polyurethane (PU) contributes significantly to solid waste accumulation. Alcoholysis technology can degrade waste PU into polyols for recycling, and the by-product (BPF) can be used as asphalt extender to produce BPF-asphalt while maintaining good performance. Based on the previous research, this study focuses on the interaction between BPF and asphalt at a molecular scale. Two types of BPF (BPF-A and BPF-B) were selected, and the molecular models were established based on their chemical compositions analyzed by nuclear magnetic resonance, which revealed their primary constituents as propylene oxide (PO), ethylene oxide (EO), and diamino diphenylmethane (MDA). The interaction energy between each component of BPF with each component of asphalt is negative, with polyether (EO/PO) showing the strongest interaction due to hydrogen bonding, followed by aromatic amine through hydrogen bonds and π-π stacking, proving that there is good compatibility between BPF and asphalt molecules. In addition, the tensile model was established to simulate the cracking behavior at different loading rates and verify the results of tensile ductility tests. The results show that the rapid tensile of molecular chains at high loading rates inhibits viscous relaxation, thereby improving the instantaneous load capacity. The excessively low loading rates may lead to the loss of energy dissipation efficiency due to excessive relaxation of the molecular structure. BPF-A, which is richer in polar EO groups, forms stronger hydrogen bonds with asphalt, yielding higher peak traction under rapid loading. Conversely, BPF-B’s rigid PO-dominated structure enables superior energy absorption and peak traction at low loading rates due to delayed molecular relaxation.