Phosphorus-containing transition metal complexes endowing polyamide 6 and its filaments with flame retardancy, low heat-release, anti-dripping and UV-blocking properties

The limited carbon layer formation during combustion causes severe melt droplet formation and excessive heat release in polyamide 6 (PA6) filaments, hindering their application in textiles. In this work, phosphorus-containing transition metal complexes PAPH-M (M = Co, Ni, Zn) were synthesized by combining 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with high oxidation state phosphorus and transition metal elements to enhance the carbonization effect of flame retardants in the PA6 matrix during combustion. By incorporating 10 wt% PAPH-Co into the PA6 matrix (PA6/PAPH-Co), a UL94 V-0 rating was achieved with no melt droplet. The peak of heat release rate (p-HRR) and total heat release (THR) of PA6/PAPH-Co decreased to 623 kW·m -2 and 56.8 MJ·m -2 , exhibiting reductions of 41.5% and 36.0%, respectively, compared to pure PA6. The exceptional flame retardancy, heat suppression and anti-dripping behaviors of PA6/PAPH-M composites were attributed to the quenching effect and barrier effect. Additionally, PA6/PAPH-M composites demonstrated exceptional UV-blocking capabilities, with ultraviolet protection factor (UPF) values of around 1900 compared to 3 for pure PA6. Melt-spun PA6/PAPH-Co filaments self-extinguished within 2 s in vertical burning tests and maintained sufficient mechanical strength for textile processing, confirming their sustained comprehensive performance post-spinning.