In this study, a series of polyimide/multi‐walled carbon nanotubes (PI/MWCNTs) composite aerogels with anisotropic properties were fabricated. First, the poly(amic acid) ammonium salt (PAS)/MWCNTs suspension was prepared by blending poly(amic acid), deionized water, triethylamine, MWCNTs, and CNT dispersant with the aid of ultrasonication treatment. Afterwards, the aqueous PAS/MWCNTs suspension was unidirectionally frozen at −65 ± 5°C, then followed by freeze‐drying. Subsequently, the PI/MWCNTs composite aerogels were obtained after thermal imidization treatment. Morphology observations revealed that PI/MWCNTs composite aerogels exhibited a “hive‐like” structure while viewed along the freezing direction, whereas a typical channel‐like pore structure was observed perpendicular to the freezing direction. This typical structure rendered PI/MWCNTs composite aerogels with anisotropic properties such as heat conduction, electrical conductivity as well as electromagnetic interference shielding effectiveness when the aerogels were characterized at different directions.

The hard segment of polyurethane foam (PUF) plays a special role in degradation and carbonization. In this work, flame-retardant hard segment (HSFR) used to promote fire resistance was synthesized successfully. The limiting oxygen index (LOI), vertical combustion, and micro-combustion calorimetry tests indicated the flame retardancy of the foam was elevated by introducing HSFR. When HSFR with an addition of 60 phr, the LOI value was increased from 17.0 to 25.5%, UL-94 reached V-0 rating, the peak heat release rate (p-HRR) and total heat release (THR) decreased by 63.9% and 10.0%, respectively. In addition, the compressive strength of HSFR-60 increased by five times. Further, the flame-retardant mechanism of HSFR was proposed. In vapor phase, HSFR could generate PO and PO 2 , which combine with flammable free radical and hinder segment decomposition. In condensed phase, HSFR could promote the dehydration and carbonization of chain and the formation of dense and graphitized char. This article provides a practical method for the preparation of green, highly effective, and durable flame-retardant PUF.

Lightweight carbon foams with excellent electromagnetic interference (EMI) shielding performance were prepared by carbonization process, using isocyanate-based polyimide foams as carbon precursors. The influence of carbonization temperature and graphene-doping on the morphological, electrical and EMI shielding effectiveness (SE) of corresponding carbon foams was studied in detail. Results showed that the addition of graphene was beneficial to the improvement of electrical conductivity and EMI shielding performance of carbon foams. The electrical conductivity of carbon foams increased with the carbonization temperature which was related to the increase of graphitization degree. Collapse of foam cells was observed at higher carbonization temperatures, which was detrimental to the overall EMI SE. The optimal carbonization temperature was found at 1100 °C and the carbon foams obtained from 0.5 wt% graphene-doped foams exhibited a specific EMI SE of 2886 dB/(g/cm3), which shows potential applications in fields such as aerospace, aeronautics and electronics.