Carbon nanotube/castor oil‐based waterborne polyurethane films with gradient structure for absorption‐dominated electromagnetic interference shielding and Joule heating

Abstract Conductive polymer composites are highly demanded for practical application in electromagnetic interference shielding and Joule heating owing to their excellent flexibility and adjustable conductivity. Herein, a thin film with a gradient structure, comprising carbon nanotube/castor oil‐based waterborne polyurethane (CNT/WPU), has been fabricated through solution mixing utilizing casting technology. Scanning electron microscopy images confirm that CNTs are enriched at the top of the obtained CNT/WPU film, leading to a low resistance value. Consequently, the resultant gradient CNT/WPU films exhibit shielding effectiveness, specific shielding effectiveness, and an absorption coefficient of 22.8 dB, 1091 dB/cm, and 0.697, respectively, indicating a predominance of absorption in the shielding capacity. The temperature at the surface of the resultant gradient CNT/WPU film reaches ~77°C at a voltage of 20 V. The film with a CNT content of 14.1 wt% exhibits a good stress of 11.7 MPa and a high module of 39.9 MPa. Therefore, the obtained CNT/WPU films can be applied as thin shielding materials or coating. Highlights Fabricating a gradient CNT/castor oil–based waterborne polyurethane films. Exhibiting shielding effectiveness of 22.8 dB and A ‐value of 0.697. Steady‐state temperature of CNT/WPU reaches 77°C at 20 V. Possessing green EMI shielding capability.