Study on Thermal Conductivities of Aromatic Polyimide Aerogels

Abstract

Polyimide aerogels for low density thermal insulation materials were produced by 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic dianhydride, cross-linked with 1,3,5-triaminophenoxybenzene. The densities of obtained polyimide aerogels are between 0.081 and 0.141 g cm(-3), and the specific surface areas are between 288 and 322 m(2) g(-1). The thermal conductivities were measured by a Hot Disk thermal constant analyzer. The value of the measured thermal conductivity under carbon dioxide atmosphere is lower than that under nitrogen atmosphere. Under pressure of 5 Pa at -130 °C, the thermal conductivity is the lowest, which is 8.42 mW (m K)(-1). The polyimide aerogels have lower conductivity [30.80 mW (m K)(-1)], compared to the value for other organic foams (polyurethane foam, phenolic foam, and polystyrene foam) with similar apparent densities under ambient pressure at 25 °C. The results indicate that polyimide aerogel is an ideal insulation material for aerospace and other applications.

Thermal Insulation Characteristics of Polybenzoxazine Aerogels

“…However, in the PBO aerogel system, when the pressure is higher than 1000 Pa, the mean free path of the gas molecules begins to decrease and the thermal conductivity increases because the pressure on the mean molecular free path may vary among different material systems. In the system of polyimide aerogels that we previously studied, when the pressure was higher than 2500 Pa, the average free path of the gas molecules changed …”

“…The thermal conductivity of N 2 is the highest, whereas that of CO 2 is the lowest. The thermal conductivity of the gas phase has a great influence on the thermal conductivity of an aerogel material . As shown in Figure , the thermal conductivity of a PBO aerogel at 3 Pa is the lowest.…”

Ultralight and Low Thermal Conductivity Polyimide–Polyhedral Oligomeric Silsesquioxanes Aerogels

“…The 10 wt% PI‐PAPSQ aerogel wt% had lower thermal conductivity than air at 150 °C. The thermal conductivities of all the aerogels tested here are much lower than those of common organic foams …”

“…The main factors determining the density of an aerogel are the total polymer concentration in the gelation solution and the shrinkage after drying. In previous investigations, the polymer concentration varied from 7 to 12.5 wt%, resulting in the lowest achievable density at 0.077 g cm −3 . Ultralow‐density polyimide aerogels have not been reported and studies on their preparation are still in progress.…”

“…Polyimide (PI) aerogels with a mesoporous structure have been found to exhibit low thermal conductivities, combined with excellent mechanical strength, high thermal stability, and good flexibility, making them ideal candidates as heat insulation materials in different applications . Linear and cross‐linked polyimide aerogels have been previously studied .…”