Melamine, halogenation

Flame retardants designated for nylon include halogenated organic compounds, phosphorous derivatives, and melamine cyanurate (160—163). Generally, flame retardants are difficult to spin in nylon because of the high loading required for effectiveness and their adverse effects on melt viscosity and fiber physical properties. 

While melamine is widely used in flexible foams as a fire-retardant, trichlorphenyl phosphate has been the preferred agent for use in rigid foams. However, the introduction of specifications stipulating halogen-free additives has led to a search for alternatives such as halogen-free phosphorus esters, red phosphorus and ammonium polyphosphate. 

Chemical compounds manufactured at petrochemical plants include methanol, formaldehyde, and halogenated hydrocarbons. Formaldehyde is used in the manufacture of plastic resins, including phenolic, urea, and melamine resins. Halogenated hydrocarbons are used in the manufacture of silicone, solvents, refrigerants, and degreasing agents. 

Phosphorus additives red phosphorus, phosphate esters, ammonium polyphosphate, melamine phosphates, melamine pyrophosphate. Some of them are halogenated. 

The use of polyols such as pentaerythritol, mannitol, or sorbitol as classical char formers in intumescent formulations for thermoplastics is associated with migration and water solubility problems. Moreover, these additives are often not compatible with the polymeric matrix and the mechanical properties of the formulations are then very poor. Those problems can be solved (at least partially) by the synthesis of additives that concentrate the three intumescent FR elements in one material, as suggested by the pioneering work of Halpern.29 b-MAP (4) (melamine salt of 3,9-dihydroxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]-undecane-3,9-dioxide) and Melabis (5) (melamine salt of bis(l-oxo-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octan-4-ylmethanol)phosphate) were synthesized from pentaerythritol (2), melamine (3), and phosphoryl trichloride (1) (Figure 6.4). They were found to be more effective to fire retard PP than standard halogen-antimony FR. 

In halogen-free polyamides, when the zinc borate is used in conjunction with red phosphorus, it cannot only display synergy in fire retardancy but also impart corrosion resistance toward metals such as copper.57 It is believed that zinc borate can trap trace amounts of phosphine derived from red phosphorus. Martens et al. reported the use of zinc borate in conjunction with melamine pyrophosphate in glass reinforced polyamide 6,6 to achieve V-0 (1.6mm). The partial replacement of melamine pyrophosphate with zinc borate can increase the CTI from 250 to 600 V.58... 

Additive flame-retardants may be more easily incorporated in polyurethane formulation. Several class of compounds have been used to improve flame retardancy of PU foams such compounds are halogen- (very often chloroalkyl-phosphate) or phosphorous-based compounds, although also other substances, like as EG, melamine, aluminum trihydrate and magnesium hydroxide, may be used. 

Patent literature reports also on halogen-free composition for PS foams, using phosphorus compound, such as RP, triphenyl phosphate, diphenyl cresyl phosphate, APP or diphenyl phosphate, and metal hydroxide such as magnesium or aluminum hydroxide.88 It is reported that PS foams containing a mixture of EG (6-10 wt%), inorganic compound (5-10 wt%) and RP, triphenyl phosphate (TPP) or 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOP)), and chalk compounds (5-10 wt%)89 or containing EG and phosphorus compounds such as RP, triphenylphosphate diphenyl cresyl phosphate, APP, melamine phosphate, resorcinol diphenyl phosphate, and dimethyl methylphosphonate in suitable amounts90 fulfills DIN 4102-B2 requirements. 

Flame retardants—Whereas halogen-containing Mannich bases arc mainly used as modifiers of macromolccular materials, as mentioned before, phosphorus derivatives arc employed as additives. These products arc obtained from phosphorous acid or phosphites 584 " and from other analogous phosphorus-containing compounds. N-Heterocyclcs, after reaction with melamine and formaldehyde (585), are also used as (lame retardants. -... 

Less than 10% of the polyamide produced is made in a flame retardant version. The best system is composed of a combination of red phosphorus and zinc borate (see table above). The only drawback of this system is its color which is restricted to brick red or black. If other colors are required, ammonium polyphosphate is used either in combination with organic flame retardants or with antimony trioxide. It is possible to manufacture a very wide range of colors in the halogen free system. Some systems make use of the addition of novolac or melamine resins. For intumescent applications, ammonium polyphosphate, in combination with other components, is the most frequently used additive. Figure 13.6 shows that fillers such as calcium carbonate and talc (at certain range of concentrations) improve the effectiveness of ammonium polyphosphate. This is both unusual and important. It is unusual because, in most polymers, the addition of fillers has an opposite influence on the efficiency of ammonium polyphosphate and it is important because ammonium polyphosphate must be used in large concentrations (minimum 20%, typical 30%) in order to perform as a flame retardant. 

The general concept is that sulfur is introduced into the organic substrate as a direct synthetic precursor of fluorine. Tlte sulfur compound is then treated with a thiophilic, soft electrophilic oxidant, for example electrophilic halogenation agents (NBS, NIS, DBH, Br2, SO2CI2 [148], Fj [149], IF5 [150], BrFj [151], 4-MePhIF2 [152], or nitrosyl cations (NO BF., ) [146] in the presence of a fluoride source (50% or 70% HF-pyridine [143], HF-melamine [144], NEt3 3HF) [147]. 

Melamine sheet molding compound Developed by DSM and Perstorp, is under the name Remel, as a dry sheet for compression molding, for applications especially in the electrical, public transport, domestic appliance, and sanitary ware industries. It complies with all recognized industrial fire test standards without need for halogen additives. With a limiting oxygen index of 95%, the V-O standard in... 

Nitrogen compounds have been developed for special applications, and halogen-free flameproofing in particular. Melamine products have proven particularly useful. They form inert decomposition (NH3, H2O, CO2, N2) and condensation products under thermal effects. 

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