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Polypyrrole has attracted more and more attention due to its low density, high conductivity, and excellent electro/photothermal conversion ability. However, the poor mechanical properties of polypyrrole limit its further application. In this work, mechanically flexible bacterial cellulose nanofibers/polypyrrole (BC@PPy) composite films were fabricated by in situ polymerization and vacuum filtration. The addition of BC improved the mechanical properties of PPy and made it have good tensile and bending capacity. The conductivity of BC@PPy films could be tuned by the polymerization time of pyrrole. The BC@PPy-6 h film displayed excellent low-voltage-driven Joule heating (up to 95.4 °C at 5 V) and high-efficiency photothermal conversion (up to 52.4 °C under 100 mW/cm2) performance. Moreover, the resultant BC@PPy-6 h film also showed outstanding electromagnetic interference (EMI) shielding effectiveness of exceeding 28.5 dB in the whole X band. Therefore, the multifunctional BC@PPy films possess high application prospects in wearable electrical devices for Joule heating, photothermal conversion, and EMI shielding.

With the rapid development of miniaturization, high power, and high integration of electronic components, multifunctional electromagnetic interference (EMI)-shielding materials have attracted tremendous attention. Herein, the flexible multifunctional EMI-shielding aramid nanofiber/polypyrrole (ANF/PPy) composite films are prepared through a facile vacuum filtration method, which exhibits excellent broadband EMI shielding performance, wearable sensing, Joule heating, and photothermal conversion. The ANF/ PPy-4 composite film with a thickness of 46 μm displays an outstanding EMI shielding effectiveness (EMI SE) of 35 dB in the frequency range of 6−26.5 GHz due to the introduction of conductive PPy. The EMI SE of the ANF/PPy-4 composite film per unit thickness can achieve 826.0 dB mm −1 . A tensile strength of 132 MPa and fracture strain of 5.2% can be achieved, indicating the superior mechanical properties of the ANF/PPy-4 composite film. Furthermore, the ANF/PPy composite film can monitor human motions (such as finger, wrist, elbow, knee, ankle, forearm, and throat) due to piezoresistive response. In addition, the saturation temperature of the ANF/PPy-4 composite film is about 77 °C at a low voltage of 5.0 V. Moreover, the temperature of the ANF/PPy-4 composite film can reach 54 °C via photothermal conversion under one sun irradiation. Multifunctional ANF/PPy composite films show enormous potential application for broadband frequency EMI shielding, wearable sensing, and personal thermal management.

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