Foam-to-Adhesive Recycling of Self-Blown Non-Isocyanate Polyurethane Foams Facilitated by Integration of Disulfide Exchangeable Bonds and Moisture

Non-isocyanate polyurethane foams (NIPUFs) are promising, safer, and more sustainable alternatives to conventional isocyanate-based counterparts dominating the foam market. Despite bearing covalent adaptable bonds, NIPUFs of the polyhydroxyurethane-type demand intensive reprocessing procedures for their recycling/repurposing. Herein, NIPUFs incorporating dynamic disulfide bonds, prepared by a water-induced process, show mechanical and thermal properties comparable to disulfide-free analogs while presenting strongly enhanced recyclability features under mild hot-pressing conditions (120 °C, 0.5–2 Tons, 30 min). Stress relaxation analysis shows a direct correlation between disulfide bonds content and relaxation time (τ) in reprocessed films. Importantly, foam hydroplasticization, typically referred to as a drawback in NIPUFs, is exploited here to accelerate bond exchange dynamics, facilitating the foam-to-film recycling at unprecedented, reduced temperature (i.e., 90 °C). Leveraging this reprocessing capacity, the films are transformed into easy-to-apply adhesives with lap-shear strengths comparable to commercial adhesives on stainless steel, glass-stainless steel, and nylon fabrics. Importantly, the NIPU adhesives showcase superior creep resistance, ductility, on-demand reversible adhesion and recyclability. This work presents a facile approach to constructing recyclable NIPUFs that can be repurposed into adhesives under mild conditions, enhancing their versatility and lifespan while addressing other key polyurethane applications.