Waste PET upcycled as phosphorus FR TPU

A PIN FR polyester diol, by phosphorus loading in solvent recycling of PET, was tested as PIN FR precursor in TPU (thermoplastic polyurethane). The phosphorus FR polyester diol was generated by dissolving / depolymerising waste PET (polyethylene terephthalate) in diethylene glycol, then reacting with adipic acid, then with CEPPA (2-carboxyethyl phenyl hypophosphite) and sodium acetate. This was then copolymerised with a glycol and MDI (methylene diphenyl diisocyanate) to generate a PIN FR TPU film (thermoplastic polyurethane). With a final phosphorus content of around 2%, LOI increased from around 27% (neat TPU) to 35% and achieved UL 94 V-0 (4 mm). The fire performance is suggested to be due to solid and gas phase actions of P and N in synergy. The PIN FR TPU also showed improved transparency and hydrolysis resistance compared to neat TPU. The authors suggest that this process reduces greenhouse emissions by more than one third compared to virgin TPU.

“Degradation-reconstruction-functional enhancement coupled upcycling of waste PET into recycled thermoplastic polyurethane with P-N synergistic flame retardancy”, Z. Jiang et al., Polymer Degradation and Stability 241 (2025) 111537 https://doi.org/10.1016/j.polymdegradstab.2025.111537

See also use of PIN FRs (ATH, zinc oxide) in solvent recycling of end-of-life PET to polyurethane foam in Vothi et al. 2024, in pinfa Newsletter n°166.Research and Innovation