Supercritical N2 induced sandwich type lightweight and strong PP/CF foams with excellent electromagnetic shielding properties

[Display omitted] •Sandwich-type PP/CF foams with supercritical N2 was proposed.•Fine, dense and uniform cellular structure was obtained.•PP/CF foams maintain a level of EMI shielding performance greater than 30 dB despite at mold opening distance of 5 mm.•Lightweight foams with both excellent strength and EMI shielding properties were prepared. The tremendous advances in communication technology and the explosion of electronic products led to an intensification of electromagnetic pollution, yet the efficient development of lightweight, high-strength fiber composite foams with excellent electromagnetic shielding properties was still a great challenge. Herein, this study, inspired by the sandwich structure, proposes a green foaming method with supercritical N2 to prepare a multilayered structure of carbon fiber reinforced polypropylene (PP/CF) foams, with a dense cellular structure in the core layer and a solid layer in the surface layer. The incorporation of CF improves the crystallization and rheological behavior of PP/CF, which guarantees a fine, dense and uniform cellular structure. This inner fine cellular structure and the solid layer on the surface contribute to the excellent mechanical properties. PP/30 %CF foam with a 1 mm mold opening distance displays an enhancement of 189.9 % in tensile strength and 196.3 % in flexural strength compared to pure PP. This also indicates more lightweight, high-strength and high-rigidity microcellular parts was obtained with less raw materials. Moreover, the formation of CF conductive network and internal foam structure contribute to excellent electromagnetic interference (EMI) shielding performance. The PP/CF composite foams maintain a level of EMI shielding performance greater than 30 dB despite the higher mold opening distance. Specifically, the PP/30 %CF foams at opening distance of 5 mm was enhanced to 58.3 dB·cm3/g with an improvement of 76.7 %. This implies that lightweight microcellular parts with both excellent strength and EMI shielding properties can be prepared, which enables PP/CF foams to possess a wide range of applications in various fields.