Mechanochemistry\nRecycling of Polyurethane Foam Through\nTranscarbamoylation Mediated by Free Alcohol

It is highly desirable to provide an effective methodology\nto recycle\npolyurethane foam (PUF) wastes into similar or even higher value products,\nwhich is expected to promote the sustainable development of the PUF\nindustry. In this work, a mechanochemical pretreatment and hot pressing\nprocess via free alcohol mediated transcarbamoylation (associative\nexchange mechanism) is proposed to reprocess commercial PUF into high\nvalue-added polymers. The effects of the content of the catalyst (<i>p</i>-toluenesulfonic acid, PTSA) and the free alcohol (−OH)\ngroups (glycerol, GLY) on the structure and properties of reprocessed\ncommercial PUF were investigated. The results showed that the tensile\nstrength increased from 11.8, 20.24, to 27.28 MPa and that the cross-linked\ndensity increased from 825.9, 1872.86, to 2469.33 mol/m<sup>3</sup> for reprocessed PUF, PUF–5 wt % PTSA, and PUF–5 wt\n% PTSA–1 wt % GLY, respectively. The relaxation time of reprocessed\nPUF sheets was greatly shortened from 9935.75 s for the PUF sheets\nto 1832.95 s and 820.05 s for the PUF–5 wt % PTSA and PUF–5\nwt % PTSA–1 wt % GLY sheets, respectively. Furthermore, PUF\nsheets could still maintain 92.3% of their tensile strength after\nthree cycles of recycling. The possible reason could be that the catalyst\nPTSA and the free alcohol GLY could accelerate the dynamic carbamate\nexchange, resulting in faster stress–relaxation and realizing\nthe multiple reprocessability of PUF. This simple method shows great\npotential for value-added recycling of commercial PUFs and improves\nthe sustainability of the PUFs industry effectively.