Production of polyimide aerogels for thermal insulation applications from recycled polyurethane-derived diamines

Abstract

This research highlights the production of polyimide aerogels for thermal insulation applications, with a focus on assessing the feasibility of using recycled diamines derived from chemically depolymerized polyurethane foams. Although polyimide aerogels are widely recognized for their low density, excellent thermal stability, and strong resistance to fire, their synthesis relies heavily on commercially available petrochemical monomers, particularly diamines such as 4,4’-oxydianiline (ODA).

In this work, a two-step synthesis route (DuPont) with freeze drying was used to synthesize aerogels, first from biphenyl tetracarboxylic dianhydride (BPDA) and ODA, by varying poly (amic acid) solid contents (3%, 5%, 7%). The 7% formulation showed the best combination of properties, including low density (0.10g/cm³), compressive modulus of 0.05 MPa, and thermal conductivity of 0.46 W/mK. This optimized condition was then used to produce aerogels with commercially obtained 4,4’-methylenedianiline (MDA). Although, the MDA based aerogels exhibited higher mechanical strength (modulus = 0.30 MPa), slightly lower thermal conductivity (0.04 W/mK), and reduced flexibility, mainly due to the greater molecular rigidity of MDA, the overall performance was comparable to that of ODA-based aerogels, indicating that MDA could be a viable substitute for ODA in polyimide aerogel synthesis.

Based on these findings, the same synthesis method was applied using MDA recovered from chemically recycled polyurethane foams. FTIR characterization confirmed the successful imidization, demonstrating the feasibility of producing polyimide aerogels from waste-derived diamines.

These results offer a promising route for converting polyurethane foam waste into high-performance insulation materials and support the transition towards more sustainable and circular polymer systems.