Interfacial bonding flame retarded coating of nylon 6: Anti-dropping, self-extinguishment and water-proof

Melt-dripping is one of the key focuses for flame retardant modification research of nylon 6 (PA6). In this paper, amine-activated cyclotriphosphazene containing siloxane (N-APESP) was prepared via two-step synthesis of cyclotriphosphazene, KH550 and 1,3-propane diamine. Then, Si-O-Si crosslinking structure containing cyclotriphosphazene, called Si-CP structure, was formed on the PA6 surface by interfacial bonding and hydrolytic condensation of N-APESP. The interfacial bonding among Si-CP structure, melamine (MA) and PA6 via the reaction of aldehyde and amino, was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was verified that there was 2–5 μm Si-CP coating containing on the PA6 surface by means of XPS depth profiling. The test results showed that the interfacial bonding Si-CP coating improved the anti-dropping, self-extinguishment and water-proof of PA6 plates. The water proof of the specimens were retained, especially for MA/PA6, with water contact angle of more than 90°. Compared with the UL-94 V-2 rating of the contrast specimens, the interfacial bonding made Si-CP@(10%MA/PA6) reach V-0 rating because of anti-dropping and after-flame time reduction. Meanwhile, the after-flame time of Si-CP@PA6 and Si-CP@(5%MA/PA6) was reduced by 76.34% and 77.56%, respectively. The flame-retardancy mechanism of the Si-CP coating was explored by thermogravimetry, cone calorimetry and char residue characterization. It was Si-CP coating that played an important role in the formation of strengthened expanded bubbly structure with rich P and Si during heating and combustion, so that the barrier effect was enhanced and the melting droplet problem was solved.