Down-Cycling Sustainability of Flexible Polyurethane Foam in Improving Asphalt Performance through a Proper Pyrolysis Approach

The down-cycling process of waste polymers in asphalt binder achieves a win–win situation in terms of economic modification and efficient disposal of valuable waste. By combining the “controllable pyrolysis” and “down-cycling” concepts, this study specified the application potential of sustainable recycling flexible polyurethane foam (FPUF) in improving asphalt performance. A proper pyrolysis method was proposed to selectively decompose waste FPUF into fibers. Subsequently, eco-friendly and cost-effective properly pyrolyzed FPUF fiber-modified asphalt (PyFMA) was developed. The microscopic, chemical, and mechanical investigations were carried out to clarify modification mechanisms and application feasibility. The results showed that the proper pyrolysis method efficiently produced flexible reticulated PFUF fibers of different sizes grafted with polar groups. The PFUF fibers interlocked spatially and well-coordinated with the asphalt matrix, contributed an elastic component in the mixed hybrid, and positively influenced the asphalt performance. The performance enhancement was the result of a combination of chemical interaction, physical reinforcement, and the volumetric filling effect. In addition, the PyFMA had adequate workability at a high fiber dosage of 24% to achieve a massive recycling goal. It is promising and feasible to use waste FPUF as a sustainable and high-performance asphalt modifier, which countermeasures the rapidly increasing abandonment and meets economical asphalt modification requirements