A TU Darmstadt thesis suggests that PIN FRs are not an obstacle to mechanical recycling of thermoplastics. Mineral, nitrogen and phosphorus based PIN flame retardants (ATH, sepiolite, aluminium diethylphosphinate, piperazine pyrophosphate, phosphate ester, APP, melamine cyanurate) were tested in various thermoplastics: polypropylene, polyethylene, polyester, polycarbonate/ABS blend, including with glass fibres and stabilisers. Material deterioration with multiple recycling (five extrusion cycles) showed to be principally related to the base polymer properties, and to shortening of glass fibres, rather than to the PIN FR used, and deterioration of fire performance to damage of anti-drip agents. In PA6 with melamine cyanurate, it was shown that use of a chain-extension additive (maleic anhydride) during re-extrusion significantly reduced polymer property deterioration.
See also summary of Fraunhofer LBF tests of mechanical recycling of PIN FR polymers (project with pinfa) in pinfa Newsletter n°105.
“Recycling von halogenfrei flammgeschützten Kunststoffen” (Recycling of halogen-free flame retardant plastics), Technische Universität Darmstadt thesis, Christoph Schultheis, 2021 https://tuprints.ulb.tu-darmstadt.de/18626/1/Dissertation_ChristophSchultheis.pdf