Abstract: The rapid development of modern 5G technology has significantly increased the demand for multifunctional electromagnetic interference (EMI) shielding and wave-absorbing materials. Hence, a densification strategy was proposed to fabricate multifunctional rigid polyimide (PI) composite foam. As a result, the composite PI foam exhibits excellent mechanical properties, with tensile and bending strengths of 4.7 and 21.1 MPa, respectively. Moreover, the composite PI foam achieves a promising EMI shielding performance with a high absorption coefficient (A) of 0.71, coupled with an X-band (8.2-12.4 GHz) EMI rating of 44 dB (2 mm) due to its high conductivity (20.29 ms/mm). Satisfyingly, the composite PI foam also has an optimal reflection loss (RL) of up to -46.4 dB and an effective absorption bandwidth (EAB) (RL < -10 dB) that covers the entire X-band. Meanwhile, the fabricated foam demonstrates a Joule heating performance of 89.2 °C under supply voltages (3-9 V) and rapid response time (within 20 s) for stable and reproducible performance in long-term cycling. This work provides a versatile strategy for the development of lightweight and high-strength materials for EMI shielding and microwave absorption, demonstrating great potential for aerospace, microelectronics, and energy conversion applications.

Key words: Polyimide foam, Microwave absorbing, Green EMI shielding, Joule heating, Flame retardancy