Fabrication and Performance of Bicontinuous Self-Healing Water-Absorbing and -Swelling Elastomers through Multiscale Synergistic Strategies

Water-absorbing expansion elastomers, valuable in environmental engineering, are limited by their low mechanical strength, poor self-healing capacity, and recycling challenges. While polyurethane (PU) offers superior mechanical robustness and weather resistance, it inherently lacks hydrophilicity. To address these gaps, this study developed self-healing, hydrophilic swelling PU elastomers via a multiscale synergistic strategy; rigid crystalline hard segments (imidazolidinyl urea) were integrated with soft segments poly(tetrahydrofuran) glycol and hydrophilic poly(ethylene glycol), and 2-hydroxyethyl disulfide (HEDS) was introduced to modulate interfacial interactions, forming a bicontinuous phase network. Fourier transform infrared spectroscopy confirmed the complete reaction of isocyanate groups, validating successful synthesis. Optical transmittance increased with poly(tetrahydrofuran) glycol (PTMEG) content, while X-ray diffraction revealed an enhanced amorphous phase intensity. Mechanically, polyurethane elastomer (PU2) achieved a toughness of 36.50 MJ/m³, and polyurethane elastomer (PU2–17%) demonstrated a tensile strength of 7.4 MPa with 731% elongation. Self-healing efficiency reached 96% (at 100 °C/6 h) with optimized disulfide bond density, though excessive HEDS slowed thermal response via dynamic bond exchange. Notably, polyurethane elastomer (PU1), containing higher PEG content, exhibited the highest swelling ratio (195% at 24 h). The hygroscopic conductive sensor sample with a sandwich structure, denoted as PU2–17%-PPy, possesses a high humidity responsiveness. Response and recovery tests indicated that it featured a humidity response time of 7 s and a full recovery time of 60 s, which was significantly faster than that of traditional humidity-sensitive materials. By synergizing dynamic bonds, soft segment design, and crystalline hard domains, this work provides a sustainable strategy for advanced functional materials, balancing mechanical durability, environmental responsiveness, and recyclability.