Preparation of durable coating for polyamide 6: Analysis the role of DOPO on flame retardancy, anti-dripping and combustion behavior

The application of insoluble 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to develop a durable coating for flame retardant (FR) modification of polyamide 6 (PA6) is of concern and difficult. This study found that the hydration reaction of DOPO provided the possibility of constructing a DOPO coating. Hence, DOPO compound was deposited onto PA6 fabric by dip-coating technique. Then, the impacts of DOPO coating on FR performance, anti-dripping property, smoke and heat release performance of coated PA6 fabric were systematically studied. The limiting oxygen index (LOI) of PA6 fabrics continued to increase with the increase of phosphorus content. However, the coated PA6 fabrics achieved anti-dripping property at a phosphorus content of 0.88 ∼1.75 mg/g. Besides, the heat release ability of coated PA6 reduced sharply at high phosphorus content of 1.75 mg/g, as suggested by a reduction of 20.9% and 21.8% in pHRR and THR, respectively. Moreover, DOPO coating exhibited good washing durability on PA6 fabric because of the hydrogen bond formed between DOPO and PA6, as well as the adhesion of DOPO coating. The coated PA6 fabric could still self-extinguish after 15 washing cycles. Further analysis proved that DOPO played a quenching role in the gas-phase with a weak condensed-phase action. This work points out the right direction for the future research on the preparation of FR PA6 fabric using DOPO derivatives.