Next to the basic flame retarding potential of pure melamine, the 'derivative' end
adds additional features. Typical examples are cyanuric acid causing a non-burning
drip in polyamides, the contribution of boric acid and phosphoric acid to char formation
and the influence of the 'derivative' end on thermal stability and water solubility
(see figure 1 and 2).
Figure 1: water solubility
Figure 2: thermogravimetrical analysis
MB: melamine borate MP: melamine phosphate MpolyP: melamine
polyposphate MC: melamine cyanurate
Melamine cyanurate, is a salt of melamine and cyanuric acid. Melamine Cyanurate
has a higher thermal stability than pure melamine, remaining stable upto about 320
°C. For this reason Melamine Cyanurate is often applied in polymers with higher
processing temperatures, like polyamides. Above 320°C, it undergoes endothermic
decomposition to melamine and cyanuric acid, acting as a heat sink in the process.
The vaporized melamine acts as an inert gas source diluting the oxygen and the fuel
gases present at the point of combustion (see Mechanism of action).
Melamine (Mono/Pyro/Poly) Phosphates
Chemical Structrure of Melamine Cyanurate
Melamine phosphates are substances combining the synergistic effect of melamine
(thus N-containing) with P-containing components in one salt. With increasing thermal
stability the melamine phosphates can be ranked as follows: Melamine Phosphate <
Melamine Pyrophosphate < Melamine Polyphosphate.
Melamine-mono-phosphate, is a salt of melamine and phosphoric acid. Above ~200°C
melamine phosphate will react to melamine pyro-phosphate with release of reaction
water, which will result in a heat sink Above ~260°C melamine-pyrophosphate
will react under release of reaction water to melamine-polyphosphates which again
results in a heat sink effect.
Above 350°C, melamine-polyphosphate undergoes endothermic decomposition thus
acting as a heat sink and cooling the combustion source. The released phosphoric
acid acts to coat and therefore shield the condensed combustible polymer. The phosphoric
acid along with the polymer also works to form a char around the fuel source (polymer)
thus reducing the amount of oxygen present at the combustion source. The melamine
released also is a blowing source to blow up the char resulting in an intumescent
In glass filled applications Melamine phosphate and pyro-phosphate will release
water and initiate degradation of the polymer due to the high processing temperatures.
Figure 4 : Chemical structure of melamine-phosphates