Phosphorus ammonium polyphosphate

The aim was to assess the feasibility of substitution with less hazardous flame retardants. They selected red phosphorus, ammonium polyphosphate and aluminium trihydroxide as the least environmentally problematic alternatives. Red phosphorus can technically be used in a variety of polymers to meet even the toughest fire safety standards, although it may network forall applications. ... 

Other flame retardants Inorganic phosphorus Ammonium polyphosphate Red phosphorus Melamines Melamine crystal Melamine cyanurate Melamine phosphates Magnesium hydroxide Molybdeniun compoimds Zinc borate... 

Phosphorus Forms char Red phosphorus, ammonium polyphosphate, organic phosphorus compounds Red phosphorus is difficult to process and toxic. Organic phosphorus compounds are a common alternative, but generally more costly and can lower Tg. 

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. 

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

Many thousands of phosphorus compounds have been described as having flame-retardant utility. The compounds demonstrating commercial utility arc much more limited in number. They include inorganic phosphorus compounds [red phosphorus, ammonium phosphates. insoluble ammonium polyphosphate, phosphoric acid-bascd systems for cellulosics). additive organic phosphorus flstme retardants... 

The largest volume use of phosphorus-based flame retardants may be in plasticized vinyl. Other use areas for phosphorus flame retardants are flexible urethane foants. polyester resins and other thermoset resins, adhesives. textiles. polycarbonate-ABS blends, and some Other thermoplastics. Development efforts are well advanced lo find applications for phosphorus flame retardants, especially ammonium polyphosphate combinations, in polyolefins, and red phosphorus in nylons, Interest is strong in finding phosphorus-bused alternatives to those halogen-containing systems which have encountered environmental opposition, especially in Europe. 

UREA-AMMONIUM POLYPHOSPHATE. A fertilizer similar fo urea-ammonium othtrophosphate except that about half the phosphorus is in polyphosphate form, which gives improved sequestering action and solubility. It is excellent for use as a liquid fertilizer. 

Ammonium polyphosphates, on the other hand, are relatively water insoluble, nonmelting solids with very high phosphorus contents (up to about 30%). There are several crystalline forms and the commercial products differ in molecular weights, particle sizes, solubilities, and so on. They are also widely used as components of intumescent paints and mastics where they function as the acid catalyst (i.e., by producing phosphoric acid upon decomposition). They are used in paints with pentaerythritol (or with a derivative of pentaerythritol) as the carbonific component and melamine as the spumific compound.22 In addition, the intumescent formulations typically contain resinous binders, pigments, and other fillers. These systems are highly efficient in flame-retarding hydroxy-lated polymers. 

Levchik, S.V., Camino, G., Costa, L., and Levchik, G.F. 1995. Mechanism of action of phosphorus-based flame retardants in nylon 6.1. Ammonium polyphosphate. Fire Mater. 19 1-10. 

Ammonium polyphosphate is one of the most often used phosphoric fertilizers (Corbridge, 1980). It was found to be equally effective when compared with single superphosphate and diammonium phosphate for increasing the yields of wheat and maize and for increasing the available phosphorus content in soil during field experiments (Sharma and Singh, 1998). 

R. D. Sharma and T. A. Singh (1998). Direct and residual effects of liquid ammonium polyphosphate as a phosphorus source in wheat (Triticum aestivum) maize (Zea mays) cropping system in an Entisol of western Uttar Pradesh. Ind. J. Agronom., 43, 223-230. 

Organophosphorus and polyphosphate compounds also have been used as fire retardants. In one study, ammonium polyphosphate was used at loading levels of 96 kg/m to achieve a flame-spread index of 15 according to ASTM E 84 (J2). This treatment produced low smoke yields however, this treatment was corrosive to aluminum, slightly corrosive to mild steel, but not corrosive to brass (77). In a patent by Clermont (78), phosphorus pentoxide, dimethylformamide, and urea were used to produce fire-retardant paper or veneer. Other patents (79, 80) describe the reaction of ammonia with partial esters of polyphosphoric acid. All patents demonstrated some leach resistance of the phosphorus. 

Poly-N [Solutia]. (ammonium polyphosphate). TM for chemical used as a phosphorus-based catalyst in organic as well as latex-based products. 

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. 

In fire retardant applications, a combination of zinc borate with ammonium polyphosphate gives V-0 rating. The use of zinc borate permits a reduction in the amount of ammonium polyphosphate. Red phosphorus alone or in combination with ammonium polyphosphate or melamine phosphate also produced a V-0 rating. The heat release rate can be effectively improved by small additions (1-2 wt%) of silicone powder in combination with other flame retarding additives or at higher concentration (15 wt%) when used by itself. 

These mechanisms, however, are not as effective in limiting the rate-of-mass loss, energy release or total mass consumption as is the formation of a monolithic, insulating char barrier. Those organophosphorus compounds most commonly used today, the chloroalkyl phosphates and the aryl phosphates, or even the inorganic ammonium polyphosphates and elemental red phosphorus are not very effective char formers in these polymer systems. 

Fire resistant PU are obtained by the addition or by introduction into the PU structure of special compounds, called flame retardants. The flame retardants are organic compounds containing halogens (chlorine, bromine) and phosphorus. Compounds of antimony (Sb) or boron [1-13] are rarely used. Sometimes inorganic compounds are used as flame retardants for PU, such as, hydrated alumina (Al203 nH20), Sb203 or ammonium polyphosphate [1-3, 14]. 

Red phosphorus itself can be used as an efficient flame retardant, as well as organic phosphorus compounds, for example, ammonium polyphosphate, bisphenol-A-diphenylphosphate, or resorcinol diphenylphosphate, or phosphorus-containing salts, for example, the aluminum salt of diethylphosphinate (Fig. 11.19). Phosphorus-containing... 

Ammonium polyphosphate appears to cross-link the polymer at high temperatures, thus increasing the probability of carbon-carbon bond formation in the condensed phase. There are, however, a number of problems with this method. For example, the temperature at which the polymer begins to degrade is decreased and, because substantial amounts of inorganic salts are required to be effective, they modify the mechanical properties of the PU foam. A particularly disconcerting observation was that under certain conditions toxic phosphorus compounds may be formed with disastrous consequences for human life. 

Phosphorus-containing flame-retardants can also be incorporated into the polyester chain. Phosphonates enter the main chain while dialkyl phosphites form side chains through scission of the double bond of maleic acid. In addition allyl or diallyl phosphites may act as cross-linking agents. Ammonium polyphosphate is sometimes admixed to the resin as a filler. 

Additive flame-retardants, however, may also be suitable, for example ammonium polyphosphate, tris(2-chloroethyl) phosphate, or other phosphorus-containing plasticizers. 

Phosphorus containing unsaturated polyesters Expandable graphite ammonium polyphosphate, triphenyl phosphate Flammability and thermal properties investigated, by UL 94 [13] and LOL Polymers containing ethylene glycol and ammonium polyphosphate showed the best flame retardance [44]... 

The 11-37-0 in Table 10.13 is an ammonium polyphosphate liquid made from superphosphoric acid, which was produced from elemental phosphorus. The 10-34-0 is the most common ammonium polyphosphate solution currently in use. It is produced from conventional wet-process superphosphoric add, and the 8-24-0 liquid was produced from orthophosphoric add made from elemental phosphorus. 

Other fertiliser compounds which can satisfactorily provide phosphorus and nitrogen are urea phosphate, CO(NH2)2 H3PO4, ammonium polyphosphate, [(NH4)P03] and phosphazenes such as P3N3(NH2)g (Table 12.4). Red phosphorus is slowly oxidised in damp soil and has been considered as a possible fertiliser [32,33]. 

Anhydrous ammonia and aqueous phosphoric acid are sometimes applied directly and simultaneously to the soil to provide N and P. Ammonium polyphosphate can be added to irrigation water. Potassium and phosphorus can be supplied together as KH2PO4, K2HPO4, (KP03) or MgKP04. 

An early fire-retardant treatment for paper and cotton was to heat them with phosphoric acid and urea at 145-180°C to form insoluble ammonium polyphosphate, (NH4P03) . Ammonium polyphosphate is also used in intumescent paint formulations, where, like the orthophosphate, it releases ammonia and phosphoric acid on heating. The latter facilitates charring which, together with the release of ammonia, retards local combustion. A similar mechanism is believed to account, at least in part, for the fire-retardant action of many other phosphorus compounds. There is now evidence that impregnation of wood with phosphoric acid suppresses the formation of carcinogenic materials during pyrolysis [39]. 

Phosphorus oxynitride (PON) is the name for a family of closely related materials that have been around for over 100 years. They are not well known but are thermally very stable and may be considered as future flame retardants and for intumescent formulations since PON is analogous to ammonium polyphosphate. It can be made from inexpensive starting materials such as ammonium phosphate, melamine phosphate or urea phosphate just by prolonged and intensive heating. 

Phosphorus containing compounds offer another route to provide halogen-free flame retardancy in thermoset composites. Ammonium polyphosphate materials promote carbonaceous chars that are bound into a vitreous coating formed by the polyphosphate decomposition products. The smoke density emitted from such systems in a fire easily satisfies the requirements of the German Bundesbahn, the French Epiradiateur test for irradiated surfaces, and Airbus requirements for smoke and toxicity. 

Intumescent flame retardants (IFR) that contains phosphorus are also used in halogen-free flame-retardant systems. Most reported IFRs are mixtures of the three ingredients, an acid source, a polyol, and a nitrogen-containing compound (Halpem et al. 1984). Since processing of ABS resin requires that the additives withstand temperatures in excess of 200 °C, the commonly used intumescent system, ammonium polyphosphate, pentaerythritol, and melamine, which do not have sufficient thermal stability, cannot be incorporated into ABS resin under normal processing conditions they are usually used in polyolefins. 

Inorganic phosphates. Inorganic phosphates consist of ammonium polyphosphate and red phosphorus. The ammonium polyphosphate product is primarily used in intumescent coatings and rubber as well as plastics. Red phosphorus is used as a flame retardant in coatings and nylon. 

Intumescent systems based on ammonium polyphosphate can produce flame retardant polypropylene. Great Lakes manufactures Reogard 1000, an intumescent phosphorus and nitrogen based, melt blendable flame retardant for polypropylene homopolymers and low ethylene PP copolymers that need V-0 ratings. It is not particularly hygroscopic and gives good electrical properties with improved heat distortion temperature. 

Flame retardant additives can also modify the types of products that are released during incineration of waste polymers and in this way the flame retardants are contaminants which also affect the quaternary recycling of polymers (that is, the incineration of polymers to recover heat). For example, the thermal degradation of polyurethane, PU, can produce a complex mixture of products. However, in the presence of a common phosphorus-based flame retardant (such as ammonium polyphosphate), aniline (which is quite toxic) becomes a relevant volatile combustion product. ... 

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