Highly Oriented CNTs Endowing PP Foam with High Electrical Conductivity and Excellent Electromagnetic Interference Shielding

Overcoming the challenge of low-conductivity polymeric foams at minimal filler loading requires innovative approaches. Herein, we present a strategy that leverages synergistic crystal structure regulation and heterogeneous nucleation to direct the alignment of the conductive medium for dramatically enhanced electrical conductivity. Polypropylene (PP) powder and carbon nanotubes (CNTs) are predispersed, followed by twin-screw blending extrusion to introduce azodicarbonamide (AC) foaming agent and nanopolytetrafluoroethylene (PTFE) particles. Lastly, hot-pressing foaming is performed to obtain the CNTs/PTFE/PP composite foam. The proposed approach enhances the foam microstructure by decreasing the cell size, increasing cell density, and aligning CNTs along the cell wall. Consequently, the conductivity increases from close to 0 to 71.6 S/cm. Moreover, the improved microstructure and extensive conductive network lead to enhanced electromagnetic interference shielding of 40.3 dB. The composite foam exhibits excellent thermoelectric and photothermal conversion performance, maintaining heating stability for 2400 s. The PTFE particles form fibrous structures during extrusion, which enhance the interfacial force and, thus, the mechanical strength. Overall, the proposed method, leveraging crystal size refinement and heterogeneous nucleation, yields composite foams characterized by enhanced conductivity, versatility, and excellent mechanical properties, with promising applications in aerospace, automotive interior shielding, and thermal management.