Flexible bilayer Ti3C2Tx MXene/cellulose nanocrystals/waterborne polyurethane composite film with excellent mechanical properties for electromagnetic interference shielding

To address electromagnetic wave (EMW) pollution, the development of ultrathin and flexible electromagnetic shielding materials is essential. High electromagnetic interference (EMI) shielding performance while retaining robust mechanical properties remains a challenging hurdle. In this work, bilayer structured MXene/CNC/WPU (MCW-X) composite films were fabricated via alternating filtration assisted by vacuum. On the one hand, a conductive network is formed between CNC and MXene nanosheets, which enhances the electrical conductivity of the composite film as well as the stable water-oxidation stability. On the other hand, the interaction between WPU and MXene nanosheets increases the sliding between the layers of MXene nanosheets, hence enhancing the tensile strength and toughness. Meanwhile, the incorporation of CNC and WPU into MXene nanosheets increases the interlayer spaces of the composite films, optimizes impedance matching, and boosts the EMI shielding performance. MCW-4.5 sample composite (CNC 20 wt%) exhibits excellent electrical conductivity of 606.1 S/cm, resulting in a high-performance EMI shielding of 54.2 dB in X-band with a thickness of 35 µm. Meanwhile, it exhibits exceptional mechanical properties (elastic modulus of 3652.70 MPa, tensile strength of 52.2 MPa). Consequently, MCW-X composite films have a significant utilization potential in the field of green, ultrathin, and flexible EMI shielding.