Production, thermal recycling, and application of cardanol-based polyurethane foam with phenol-carbamate bonds

The economic processing, sustainable recycling, and environmentally friendly application of polyurethane (PU) foams are important issues that need to be addressed urgently. In this study, we propose a strategy for the comprehensive utilization of cardanol and cashew shells to design cardanol-based PU (CPU) foams and wood-plastic films that can be recycled and reused. Firstly, cardanol-based polyphenols (CBPs) with a phenolic hydroxyl content of 3.29 mmol/g were prepared by Friedel-Crafts alkylation reaction using cardanol and guaiacol as raw materials. Subsequently, CPU foams were prepared by reacting CBPs with isocyanate, and the vertical and parallel compressive strengths could reach up to 0.27 MPa and 0.32 MPa, respectively, when the addition of CBPs was 80 %. These CPU foams, containing dynamic phenol-carbamate bonds, could be hot-pressed into transparent and smooth CPU films with tensile strengths of up to 30.5 MPa and could be re-formed at least three times. Finally, CPU foam and cashew shell waste were mixed and hot-pressed to produce a green wood-plastic composite with a tensile strength of up to 38.8 MPa. The resulting CPU-Wood films could be repaired or reshaped at least five times (38.0 MPa and 38.1 MPa) and could be formed into various shapes. This research paves the way for large-scale industrial production of recyclable and regenerative bio-based foams, making effective use of waste materials to achieve environmentally friendly production processes.