Recycling of PET fibres with different phosphorus PIN FRs showed that combinations can achieve excellent stability. PET (polyethylene terephthalate) was mechanically recycled with three reprocessing cycles @ 275 – 305 °C (extrude, quench, melt-spin) neat and with two different commercial PIN phosphorus flame retardants: a DOPO derivate DOPO-PEPA @ 5% loading and a phosphonate compound @ 3% loading. The phosphonate FR hindered recycling by causing cross-linking/chain-branching, making the recycled compound too brittle to melt-spin, but this was resolved when combined with the DOPO-PEPA. The two PIN FRs together enabled stable viscosity during reprocessing, efficient fire protection of the recycled compound and maintained mechanical properties (tensile strength). This confirms similar results with this PIN FR DOPO derivative in polyester (Bascucci 2022 in pinfa Newsletter n°136).
“Mechanical recycling of PET containing mixtures of phosphorus flame retardants”, J. Chen et al., J. Science & Technology, 2024, https://doi.org/10.1016/j.jmst.2024.01.035 See also J. Chen poster at FRPM 2023 in pinfa Newsletter n°151.