Cardanol-Based Reprocessable Poly(urethane-urea) Foams via Hindered Urea Bonds

Polyurethane foams (PUFs) are widely used in construction, transportation, furniture, and cushioning applications because of their low density and excellent thermal and mechanical properties. However, most conventional PUFs are produced from petroleum-based resources and have permanently crosslinked network structures, making recycling and reprocessing difficult. Therefore, the development of sustainable and recyclable polyurethane foams has attracted increasing attention. In this study, bio-based polyols were synthesized from cardanol glycidyl ether derived from cashew nutshell liquid and aliphatic diamines with different chain lengths. The synthesized polyols were used to prepare both rigid and soft poly(urethane-urea) (PUU) foams. To introduce reprocessability, hindered urea bonds (HUBs) were incorporated into the polymer network. These dynamic bonds allow network rearrangement under heat while maintaining the crosslinked structure. The prepared foams were characterized by FT-IR spectroscopy, SEM, thermal analysis, and mechanical testing. All foams showed well-defined cellular structures, high gel contents, and good thermal stability. The chain length of the diamines influenced the morphology and mechanical properties of the foams. In addition, the HUB-containing PUU networks exhibited effective stress-relaxation behavior and could be reprocessed by hot pressing. The reprocessed materials retained their chemical structures and mechanical performance, indicating the stability of the dynamic network during reprocessing. These results demonstrate that cardanol-based PUU foams containing HUBs are promising sustainable alternatives to conventional polyurethane foams and provide a practical approach for developing recyclable and high-performance foam materials.