A novel cross-linked triazine phosphine polymeric flame retardant additive polymelamine tetramethylene
phosphonium sulfate defined as PMTMPS was synthesized by the condensation polymerization
between melamine and tetrahydroxymethyl phosphonium sulfate. Its chemical structure was well
characterized by Fourier transform infrared (FTIR) spectroscopy, 13C and 31P solid-state nuclear magnetic
resonance. The synthesized PMTMPS and curing agent m-phenylenediamine were blended into epoxy
resins to prepare flame retardant epoxy resins thermosets. The effects of PMTMPS on fire retardancy and
thermal degradation behavior of the cured EP/PMTMPS composites were investigated by limiting oxygen
index (LOI), vertical burning test (UL-94), cone calorimeter measurement (cone) and thermogravimetric
analysis (TGA) tests. The morphologies and chemical compositions of char residues for cured epoxy
resins were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy
(XPS), respectively. Moisture resistant properties of epoxy resins thermosets were evaluated by putting
the samples into distilled water at 70 C for 168 h. The results demonstrated that the cured EP/11 wt %
PMTMPS composites successfully passed UL-94 V-0 flammability rating and the LOI value was as high as
32.5%. The TGA results indicated that the incorporation of PMTMPS stimulated epoxy resins matrix
decomposed and char forming ahead of time, which led to a higher char yield and thermal stability for
epoxy resins thermosets at high temperature. The morphological structures and the analysis results of
XPS for char residues of thermosets revealed that the introduction of PMTMPS benefited to the formation
of a sufficient, more compact and homogeneous char layer with rich flame retardant elements on the
materials surface during burning, which prevented the heat transmission and diffusion, limited the
production of combustible gases, inhibited the emission of smoke and then led to the reduction of the
heat release rate and smoke produce rate. The results of water resistance tests shown the moisture
absorption of EP/PMTMPS thermosets was lower than that of pure epoxy resins thermosets and the
samples still remained excellent flame retardancy after water resistance tests