PET-upcycled and Biobased Hyperbranched Polyesters for Selfhealable and Flame-retardant Powder Coatings

Abstract

Although polyester powder coatings are widely utilized due to their volatile organic compound (VOC)-free processing, they still exhibit deficiencies in balancing sustainable carbon sources, regulatory compliance, in-service repair and fire safety. In this study, we introduced a “recycled + renewable” structural design strategy that involves use of tetrafunctional polyol (THETA) from PET-upcycling, and renewable chemicals for synthesis of flame-retardant and self-healable polyester powder coatings. In specific, hyperbranched polyesters (HBPEs) rich in free hydroxyl and carboxyl groups were synthesized using THETA, succinic acid and a phosphorus-containing diacid derived from itaconic acid. A resveratrol-derived tri-epoxy was synthesized and used as the curing component for HBPEs, resulting in crosslinked materials with transesterification-enabled vitrimeric behaviors. The powder resin system demonstrates stable melt-compounding, powder production, spraying, and curing within the powder processing window, showcasing thermally triggered network rearrangement and scratch self-healing properties. The phosphorus-containing structure provides synergistic flame retardancy through gas-phase quenching and condensed-phase char formation, delivering enhanced thermal protection on both steel plates, medium-density fiberboard, and basswood plywood. The results indicate that recycled carbon sources (from PET) and renewable feedstocks can be effectively integrated within the same network, providing a validated pathway for achieving systematic synergy among sustainable raw materials, self-healing, and fire safety in polyester powder coatings.