A solvent-free, self-emulsified and heat-responsive polyester coating enables chemically-recyclable and fire-safe PET foam†

A circular economy of the wind energy industry has attracted global attention. Poly(ethylene terephthalate) (PET) foam is widely used in wind turbine blades to lighten their weight, but it is highly flammable and difficult to recycle without catalysts. Herein, a coating-triggered “proactive fireproofing and recycling” strategy is proposed to achieve high fire safety during the service life and chemical recyclability after the decommissioning of PET foam. The coating is prepared by self-emulsifying polyester (containing phosphaphenanthrene and guanidine-sulfonate groups) in water without emulsifiers, organic solvents, stirring or heating and exhibits 80% ultrahigh solid content. At high temperature in fire accidents (>292 °C), the coating, as a protective layer, ensures the high fire safety of PET foam by radical scavenging and acid-catalyzed char formation. At a lower temperature (160 °C), the coating, as a macromolecular catalyst, triggers the chemical recycling of both PET foam and the coating by hydrogen bond catalysis. Thus, this work enables the life cycle management of PET foam from the service stage to decommissioning, paving the way for a green sustainable circular economy of wind turbine blades.