Synthesis and mechanical property of hexasubstituted cyclotriphosphazene derivatives attached to hydrazine-bridge linkage with high fire retardancy

Abstract

A series of new flame retardant-based hexasubstituted cyclotriphosphazene compounds, 4a-c attached to hydrazine bridged linkage with different terminal lengths (pentyl, nonyl, and decyl) was successfully synthesized and characterised. The structures of these compounds were characterised using Fourier-transform infrared (FTIR), nuclear magnetic resonance (NMR), and CHN elemental analysis. Further study on the fire-retardancy property was done using thermogravimetric analysis (TGA) and limiting oxygen index (LOI). Epoxy resin (EP) was used as a matrix of moulding for the study. The TGA curve showed that the pure EP exhibited 8.8 wt.% residues at 600°C. The char yield of compounds 4a, 4b, and 4c were 9.15, 10.30, and 11.34 wt.%, respectively. Based on the LOI values, compounds 2a-c, 3, and 4a-c showed a good increment as a material with fire retardancy. Compounds 4b and 4c attached to the nonyl and decyl terminal alkyl group gave the highest LOI value of 26.28%. The FESEM of composite EP/4c showed a condensed and compact structure indicating the char layer's formation to prevent the fire from spreading. Moreover, the mechanical property of these compounds was also investigated. The trend of mechanical properties reported are EP < 4c < 4b < 4a. The mechanical test result showed the addition of compounds 4a-c affects the flexibility and their dilution onto the polymer matrix.