Flame Retardants Center >> Melamine Compounds Center

Melamine derivatives

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

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).

Chemical Structrure of Melamine Cyanurate
Figure 3: Chemical Structrure of Melamine Cyanurate

Melamine (Mono/Pyro/Poly) Phosphates

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 behavior.

In glass filled applications Melamine phosphate and pyro-phosphate will release water and initiate degradation of the polymer due to the high processing temperatures.

Chemical structure of melamine-phosphates
n=1 melamine-phosphate,
n=2 melamine-pyrophosphate
n>2 melamine-polyphosphate

Figure 4 : Chemical structure of melamine-phosphates


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