In order to improve the electromagnetic wave absorbing performance of carbon fiber cloth at low frequency and reduce the secondary pollution caused by the shielding mechanism, a flexible sandwich composite was designed by a physical mixing coating process. This was composed of a graphene layer that absorbed waves, a carbon fiber cloth layer that reflected waves, and a graphite layer that absorbed transmitted waves. The influence of the content of graphene was studied by a control variable method on the electromatic and mechanical properties. The structures of defect polarization relaxation and dipole polarization relaxation of graphene, the interfacial polarization and electron polarization of graphite, the conductive network formed in the carbon fiber cloth, and the interfacial polarization of each part, combined together to improve the impedance matching and wave multiple reflections of the material. The study found that the sample with 40% graphene had the most outstanding absorbing performance. The minimum reflection loss value was −18.62 dB, while the frequency was 2.15 GHz and the minimum reflection loss value compared to the sample with no graphene increased 76%. The composites can be mainly applied in the field of flexible electromagnetic protection, such as the preparation of stealth tent, protective covers of electronic boxes, helmet materials for high-speed train drivers, etc.

Herein, the application of a low-cost, multifunctional polypyrrole hollow tube composite was investigated in the building field. Firstly, polydopamine was made on the surface of a polyethylene geotextile that was the base material. Secondly, the complexes of FeCl3 and methyl orange as soft templates were used in the in situ polymerization method to prepare a multifunctional polypyrrole hollow tube/polyethylene geotextile composite. Polydopamine played a role in improving the adhesion between the polyethylene fibers and polypyrrole hollow tubes. Finally, the electromagnetic shielding, sound absorption, piezoresistive sensing, and electrochemical properties of the composite were tested. The results showed that the shielding effectiveness value of the composite was higher than 32.7 dB in the X-band, which can shield at least 99% of electromagnetic waves. The average sound absorption coefficient value of the composite was 0.36, which was doubled compared with the polyethylene geotextile, and the peak sound absorption coefficient value reached 0.85 at the frequency of 5437 Hz. The composite could respond to deformation in the range of 4.9–99.9 kPa, and the highest sensitivity was 2.01 kPa−1 at a pressure of 14.2 kPa. The composite had an electrochemical response to KOH solutions, and the specific capacitance was 78.78 F/g at a sweep speed of 0.01 V/s. The composite had the advantages of simple preparation, low cost, and a wide range of use, and had broad application prospects in solving the increasingly severe electromagnetic interference, noise pollution, building structure nondestructive monitoring, and energy storage.

Zeolitic imidazolate framework (ZIF) materials have advantages such as large specific surface area, high porosity, adjustable skeleton structure, and easy functionality, but their poor electrical conductivity limits their application in the field of piezoresistive sensors and electrochemistry. To solve this problem, we prepared polypyrrole hollow tubes on the surface of polyester-cotton fabric using the soft template method and in situ polymerization method, the cross-leaf ZIF-L (L means leaf shape) was grown on the surface of polypyrrole hollow tubes using the in situ growth method, and the properties of piezoresistive sensing, electrochemistry, and surface wettability were tested. The experimental results showed that the three-dimensional network structure polypyrrole hollow tube/cross-leaf ZIF-L composite combined the advantages of polypyrrole hollow tube and ZIF-L materials, and the average sensitivity reaches 6.12 kPa−1, which was 5.3 times that of the polypyrrole hollow tube composite, and 1.9 times that of the cross-leaf ZIF-L composite. As an excellent energy storage material, the specific capacitance was 42.4 F · g−1 at a scan rate of 0.01 V/s. The composite was also an excellent superhydrophobic material, and its contact angle was up to 168.5°, which can facilitate the practical application of sensor materials and electrode materials. Polypyrrole hollow tube/cross-leaf ZIF-L composite had advantages of a simple process, thin thickness, light weight, and low price, and can be widely used in the field of smart wearables.