EMI shielding, thermal and antibacterial performances of ecofriendly castor oil–based waterborne polyurethane favored by combining carbon nanotube and cetyltrimethylammonium bromide

Many ecofriendly and antibacterial polymer-based shielding nanocomposites have been designed to address the increasingly serious issues of electromagnetic interference (EMI) pollution and antibiotic resistance. These composites contain high amounts of conductive and antibacterial material and exhibit an unsurpassed EMI shielding performance and strong antibacterial properties. However, it is extremely challenging to prepare these materials because of the formation of large aggregates coupled with the high viscosity. Herein, carbon nanotubes (CNTs) and an antibacterial surfactant (cetyltrimethylammonium bromide (CTAB)) are mixed with castor oil–based waterborne polyurethane (WPU) via ultrasonic-assisted solution mixing followed by a freeze-drying approach. Owing to the presence of CTAB, CNTs (at a concentration of 24.3 wt%) are evenly dispersed and connected to each other in the WPU matrix. This morphology and intrinsic characteristics of CNTs enable the resultant CNT/WPU composites to exhibit an excellent electrical conductivity (635.8 S/m) and thermal conductivity (0.308 W/(m·K)) as well as an incomparable shielding effectiveness (SE, 88.81 dB). Notably, the specific SE reaches 997.4 dB/cm, which exceeds those of the reported composites. Moreover, the combination of CNTs and CTAB improves the antibacterial activities of the WPU composites. Due to these merits, the resultant composites have great potential for applications in portable and wearable smart electronics. Overall, this study opens a new way toward the manufacture of ecofriendly and multifunctional polymer composites.