Thermosetting Auxetic Polyurethane/Epoxy Hybrid Foams with Enhanced Oil Resistance

Abstract To reduce liquid volatilization in oil tanks, lightweight sealing materials with high strength and oil resistance are highly desirable, as conventional polyurethane foams lack such features. This study presents a thermosetting auxetic polyurethane/epoxy hybrid foam (APUEF) enabled by synergistic molecular and cellular structure design. The foam was synthesized via one-step chemical foaming using polyethylene glycol, polyaryl polymethylene isocyanate, and a multifunctional epoxy resin (TDE-85), followed by triaxial hot-pressing (THP). TDE-85 functioned both as an oleophobic modifier and as a source of dynamic ester bonds, facilitating transesterification-driven topological network rearrangement during THP. This process concurrently transformed the conventional honeycomb-like cellular architecture into a stable re-entrant microstructure. The resulting APUEF exhibited a negative Poisson’s ratio (minimum of −0.17) under compressive strains up to 35%, along with a high specific compressive strength of 25.7 N m g–1 at 80% strain and improved oil repellency (oil contact angle of 109°). Leveraging its dynamic covalent network, waste APUEF could be physically recycled into transparent films and glass/carbon fiber-reinforced composites, demonstrating potential for material upcycling. This work establishes a design strategy for advanced multifunctional foams with promising applications in antipermeation systems.