Polyimide foams with high porosity in the micrometer range prepared by scrape foaming for thermal insulation

Polyimide (PI) foams possess excellent mechanical properties and high-temperature resistance, which present significant utility in the aerospace, transportation, and microelectronics industries. The microstructure of PI foam, specifically the pore size and porosity, significantly influences its physical and mechanical properties. However, achieving both high porosity and small pore size simultaneously is greatly challenging for PI foams, especially via the foaming method. Here, we report PI foams with mean pore size of 98.1 μm and porosity of 92 % using a one-step scrape foaming method. The scraping thickness is found to be key to adjusting the pore size of the foam due to the interface effect in the initial stage, and maintaining optimal air pressure and low temperature allows slow bubble growth without bursting or merging, resulting in PI foams with high porosity and small pore size. The PI foam we fabricated exhibits excellent thermal insulating performance, with a low thermal conductivity of 20 mW/m∙K. The scrape foaming method provides an efficient and low-cost strategy for the preparation of PI foams with a tunable porous structure and is expected to find a variety of applications in thermal insulation and environmental protection.