Application of Solid‐State Shear Milling Technology in Waste Rigid Polyurethane Recycling

ABSTRACT Polyurethane foam (PUF), valued for its low density and exceptional mechanical performance, has found extensive industrial applications. However, escalating demand has resulted in substantial waste accumulation, posing urgent environmental concerns. Aligned with carbon neutrality objectives, this study proposes a sustainable strategy for recycling rigid PUF (R‐PUF) waste through solid‐state shear milling (S 3 M). The mechanochemical process successfully reduced the average particle size of R‐PUF to 55.91 μm while inducing molecular chain motion, characterized by molecular chain recombination and increased surface roughness. The resultant polyurethane powder was functionalized with a silane coupling agent and reintroduced into polyol matrices, forming chemically crosslinked interfaces that enhanced composite performance. Systematic investigations revealed that milling cycles critically influenced surface functional groups and powder morphology, while optimal mechanical properties were achieved at 3 wt.% filler loading, increasing compressive strength from 1.2 to 1.3 MPa. Silane modification further amplified compressive strength by 80% (0.5 → 0.9 MPa) compared to untreated R‐PUF and non‐modified milled powders. These enhancements are attributed to the mechanochemical restoration of thermoplasticity and interfacial bonding via silane‐mediated covalent linkages. This work establishes S 3 M as an eco‐efficient methodology for transforming thermoset foam waste into high‐value composites, advancing circular economy principles in polymer recycling.