From Waste to Resource: Valorizing Hard Segments from Acidolyzed PU Foam as Additives in PVC

The escalating production of plastic waste underscores an urgent need for sustainable polymer recycling. Polyurethane (PU) foam, representing over 50% of PU output, is particularly challenging to recycle due to its crosslinked structure. While chemical degradation can recover polyols, the hard segment residues (PUSR) remain underutilized. This study presents an innovative strategy for upcycling waste PU foam into a value-added flame retardant. Through a tailored chemical alcoholysis and phosphorylation process, PUSR was converted into a novel "three-in-one" flame retardant (P 1 D 1 ), integrating carbon, acid, and gas sources. When incorporated into soft polyvinyl chloride (PVC), P 1 D 1 endowed the composite with a UL-94 V-0 rating and a limiting oxygen index of 24.2%, significantly enhancing its flame retardancy. Remarkably, this improvement was achieved without compromising mechanical properties, as evidenced by a 42% increase in elongation at break. This work not only establishes a promising path for PUSR valorization but also provides a sustainable solution for developing high-performance flame-retardant polymers.