Cotton-based sandwich architectures for flexible electromagnetic interference shielding materials with superior flame retardancy

Electromagnetic pollution is becoming significantly serious. Therefore, it is critical to prepare the advanced electromagnetic interference (EMI) shielding materials with thinness, flexibility and high mechanical strength. Herein, the copper-based metal-organic framework (MOF-Cu) and polyethyleneimine-modified ammonium polyphosphate (PEI-APP) were successfully synthesized. The flame-retardant thermoplastic polyurethane (TPU) composite was successfully prepared by compounding MOF-Cu and PEI-APP. The Cotton@PDA@MXene composite was fabricated via a sequential loading process of polydopamine (PDA) and MXene onto cotton fabric. Then, the multilayer TPU composites were prepared by layer-by-layer hot-pressing. The TPU/9P-APP/1MOF/C-3PM composite exhibited exceptional EMI effectiveness of 20.5 dB in X-band and 23.0 dB in K-band, exceeding commercial standards. The TPU/9P-APP/1MOF/C-3PM composite also demonstrated significantly enhanced flame retardancy. Compared with pure TPU/cotton sample, the peak heat release rate, total heat release and total smoke release of TPU/9P-APP/1MOF/C-3PM composite decreased by 40.7%, 31.1% and 33.3%, respectively. Furthermore, the thickness of the multilayer TPU composites was only 1 mm, demonstrating excellent flexibility. As the outer encapsulation material, TPU endowed the multilayer TPU composites outstanding durability and effectively addressed the common issues of fabric abrasion and conductive filler detachment. This study provides a novel strategy for preparing flexible electromagnetic interference shielding materials with superior flame retardancy.