Spinel-Reinforced Waterborne Polyurethane Coatings: Dual Near-Infrared-Induced Self-Healing and Efficient Microwave Absorption

The rapid growth of the electronics industry, along with the increasing need for flexible and portable electronic devices, has resulted in serious electromagnetic wave (EMW) hazards. Therefore, the development of multifunctional microwave-absorbing materials (MAMs) with durable performance after mechanical damage is crucial for next-generation electronics. Herein, we prepared an eco-friendly castor oil-based waterborne polyurethane (CWPU) nanocomposite coating by incorporating metal–organic framework (MOF)-derived or conventional spinels (M = Mn, Zn, and Ni), polyaniline (PANI), and polydopamine (PDA). The PDA/MOF-derived NiCo2O4/PANI sample exhibited a high microwave absorption with a deep reflection loss (RL) of −37.834 dB and an effective absorption bandwidth (EAB) of 4 GHz at a thickness of 1.3 mm in the X-band. As a result of the photothermal effect of PDA and hydrogen bonding, the nanocomposite showed a healing ability under near-infrared (NIR) light. The healed CWPU3 (0.75 wt % PDA) has the highest mechanical strength (2.121 MPa) and a self-healing efficiency (SHE) of 66% after 4 h of NIR light irradiation. This work offers a facile method for designing CWPU-based MAMs with dual functionality for smart electronics.