Synthesis of tung oil-based polyphenols via phosphotungstic acid loaded tung meal-based carbon-catalyzed Friedel-Crafts alkylation: A smart way to access renewable bio-based polyurethanes

Achieving green preparation and economical recycling of polyurethane (PU) foams while considering environmental protection and comprehensive resource utilization is a significant challenge. Herein, we have proposed an integrated utilization strategy of tung oil fruit to design tung oil-based PU (TPU) foams with malleability and thermal processability. Phosphotungstic acid was first loaded onto tung meal-based carbon derived from the solid microwave carbonization of waste tung meal to obtain carbon-based catalysts with a total acid density of up to 2408.4 μmol/g. In the Friedel-Crafts alkylation reaction of tung oil and guaiacol, the carbon-based catalysts show highly catalytic performance and reusability, resulting in the phenolic hydroxyl content of tung oil-based polyphenols reaching 3.05 mmol/g. The TPU foams containing phenol-carbamate bonds were prepared from tung oil-based polyphenols, which can be processed into TPU films through thermal compression molding. The recycled TPU films show tunable mechanical properties and can be further reprocessed. We have also produced carbon fiber-reinforced composites with TPU as the matrix, which have good mechanical properties and can be sustainably recycled. This research aims to produce closed-loop recycling-oriented TPU foams using forest resources as raw materials while adequately using waste to achieve green production processes.