Mechanochemistry recycling of polyurethane foam using urethane exchange reaction

Although the recycling and reuse of polyurethane foam (PUF) is a promising route to deal with this type of waste commodity polymer, highly efficient and green processing protocols are a great challenge due to their stable crosslink structure. In this study, a strategy of urethane exchange reactions was proposed to transform commercial rigid PUF into PUF sheets. The process was composed of the pulverization of the foam, the pretreatment method and the hot pressing. The effects of the pretreatment method on the structure and properties of the recycled commercial PUF were studied. The results show that the ball milling pretreatment method can effectively pulverize the commercial PUF into powder of 74.5 µm and a specific surface area as high as 2991.0 m2/kg, which can promote the urethane exchange reaction in close contact with the catalyst. The recycle method of ball milling pretreatment makes the crosslink density and tensile strength of the PUF sheets reach 2236.8 mol/m3 and 32.6 MPa, which means an increase of 9.9 times and 3.3 times, respectively, compared to the method of other pretreatment. Moreover, PUF sheets can still maintain 71.5% of the tensile strength after two cycles of recycling, indicating the potential of this recycling method for PUF. This simple and efficient method enhances the sustainability of rigid PUF utilization and shows the enormous potential for value-added recycling of thermosets.