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Abstract
The aim of this review article is to show the most recent research on obtaining waterborne polyurethane (WPU) coatings and adhesives using polyester polyol from polyethylene terephthalate (PET) waste, and describing their properties, in the search for a more sustainable product. WPU is obtained in two stages: (1) PET-based polyester polyol synthesis and (2) WPU synthesis. In the first stage, glycolysis is the most widely used degradation method for PET and zinc acetate catalyst to obtain polyester polyol, resulting in oligoesters. Studies with different degradation agents (propylene glycol, triethylene glycol and polyethylene glycol) of PET were highlighted, resulting in different oligoesters. A trend was observed in polyester polyol from the reaction of the post-consumption PET oligoester of using vegetable oil, particularly castor oil. A promising process was also found to obtain PU from polyester polyol in a single stage with renewable oil, which traditionally involves two stages. In the second stage, the processes using acetone solvent and prepolymer mixture were the most commonly used to prepare WPUs. The different synthesis pathways result in different WPU properties, which consequently serve different markets. It was found that adding polyester polyol to the flexible segment of WPUs (synthesized with PET and vegetable oil) led to a more flexible product, an important quality for coatings and adhesives. The presence of cutting agents, chain extenders and nanoparticles had a positive influence on the thermal stability of WPUs. The thermal degradation temperature of WPUs increased by up to 19 °C when PET oligoesters were used for their synthesis, compared to those synthesized without PET oligoesters. Moreover, the initial WPU degradation temperature can increase by up to 60%, depending on the type of glycol (propylene glycol, triethylene glycol, polyethylene glycol) and the PET/glycol molar ratio used in oligoester synthesis (1:2 or 1:10).
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1 Universidade Federal do Rio de Janeiro, IMA, Instituto de Macromoléculas Professora Eloisa Mano, Rio de Janeiro, Brazil (GRID:grid.8536.8) (ISNI:0000 0001 2294 473X)
2 Universidade Federal do Rio de Janeiro, IMA, Instituto de Macromoléculas Professora Eloisa Mano, Rio de Janeiro, Brazil (GRID:grid.8536.8) (ISNI:0000 0001 2294 473X); Universidade Federal do Rio de Janeiro, Escola Politécnica/Programa de Engenharia Ambiental, Rio de Janeiro, Brazil (GRID:grid.8536.8) (ISNI:0000 0001 2294 473X)