Looking for solvent-free, low toxicity, reactive phosphorus PIN flame retardancy for polyamide (PA6). A reaction-extrusion process was tested to generate phosphorus-containing modified polyamide, containing also phosphorus oligomers. This was then melt-spun to textile fibres, then tested for fire performance and phosphorus leaching. The inputs to the solvent-extrusion were DVPPO (divinyl phenyl phosphine oxide) and piperazine (which contains N), generating phosphine oxide macromolecules which largely reacted onto the PA6 polymer molecules (cross-linking) and a final P content of 0.73% w/w. The phosphine oxide macromolecules provided a lubricating effect, but tensile strength of the P containing PA6 was somewhat lower than neat PA6. The treated PA6 showed zero leaching in water of phosphorus (after 16 hours) from the treated PA6. After pressing into 1 mm plates, fire tests showed that the treated PA6 had a +20% higher LOI, and 50% reduced vertical burn, with afterburn reduced from 18 to 1 second. ROS (reactive oxygen species) in vitro testing of the DVVVPO suggested low toxicity.
“Michael addition in reactive extrusion: A facile sustainable route to developing phosphorus based flame retardant materials”, P. Simonetti et al., Composites Part B 178 (2019) 107470 https://doi.org/10.1016/j.compositesb.2019.107470