Polyimide aerogels with low thermal conductivity and high-temperature stable properties prepared by lyophilization for flexible thermal protection

Abstract

Polyimide aerogel, presenting an outstanding new material for lightweight protective thermal insulation, has garnered significant attention in the aerospace field. Despite its potential, due to the high production cost of the supercritical drying method used for its preparation, its widespread application is limited. In this research, a series of lightweight polyimide aerogels (F-PIAs, 3,3',4,4'-biphenyl tetracarboxylic dianhydride (s-BPDA) and 4,4'-diaminodiphenyl ether (ODA)) with excellent thermal protection properties were prepared by lyophilization. The findings indicated that F-PIAs (Freeze-dried polyimide aerogels) exhibited comparable physical characteristics to S-PIAs (Supercritical-dried polyimide aerogels), while their preparation cost was even more economical. F-PIAs exhibits excellent flexible and compression behavior (compression strength up to 1.16 MPa, modulus up to 12.8 MPa), which provide a great structural basis for the production of molded thermal insulation protective materials. The average pore diameter of F-PIAs is in the range of 7∼11 nm. The nanoporous structure leads to the gas within the pores of the aerogel producing the Knudsen effect, thereby significantly enhancing the thermal insulation performance of the aerogel. The thermal conductivity of F-PIA-4 (Freeze-dried polyimide aerogels with a solid content of 4%) at room temperature is as low as 0.023 W·m−1·K−1, which is superior to the PIAs (0.043 W·m−1·K−1) prepared by lyophilization in literature. Its thermal diffusion coefficient changes from 0.108 mm2·s−1 to 0.18 mm2·s−1 in the temperature range of 27°C to 200°C, demonstrating good thermal insulation performance at high temperatures. Meanwhile, after heating on a 150°C flat plate for 11 min and 41 s, the surface temperature of F-PIA-4 was only 36.2°C, further verifying its excellent thermal insulation performance. The results of the TGA experiment on F-PIA-4 demonstrated the high-temperature stability of aerogel (Td5% is higher than 523°C, Td10% is higher than 566°C). The exceptional properties of F-PIAs hold significant practical reference value in helping to reduce the manufacturing cost of high-performance aerogel thermal insulation materials, thereby enabling their widespread application in aerospace, military, and civil field.

Preparation of anisotropic polyimide aerogels for thermal protection with outstanding flexible resilience using the freeze-drying method

“…The peak at 9 ppm can be attributed to the ether carbon atom. 3 These 13 C NMR results further confirm that the matrix synthetic material of aerogel is polyimide. The density and contraction rates of PIAs samples are illustrated in Fig.…”

“…According to ref. 1 and 3, these peaks can be attributed to the absorption peaks generated by the vibration of C–N bonds in polyimide molecules. There are also strong characteristic absorption peaks within the 1400–1500 cm −1 range, which can be attributed to the N–H bond deformation vibration in the polyimide molecular chain.…”

“…PIA-5 maintains its outstanding thermal insulation performance even at elevated temperatures, outperforming PIAs produced from the flexible monomer ODA using a supercritical device (0.106 mm 2 s −1 ). 3…”

“…The thermal diffusivity of PIA-5 in the radial direction at room temperature is as low as 0.067 mm 2 s −1 , and even at 200 °C, the thermal diffusivity is as low as 0.057 mm 2 s −1 . Meanwhile, the thermal diffusivity in the axial direction at room temperature is 0.11 mm 2 s −1 , surpassing the value of 0.106 mm 2 s −1 of aerogels prepared from monomeric raw materials and dried under supercritical conditions 3 ). These PIAs exhibit outstanding thermal stability (the axial strength and modulus retention of PIA-8 at 200 °C are as high as 52.63% and 44.82%), and its weight loss temperature of 5% is as high as 603 °C and glass softening temperature of 387 °C.…”

“…During the development of spacecraft, researchers discovered that the search for a lightweight, thermally stable insulation material has become a pivotal factor. 1–10…”