Multifunctional rigid polyimide foams with outstanding EMI shielding and wave absorption via densification strategy

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.