Ammonium polyphosphates

This material is an inorganic salt of polyphosphoric add and ammonia with the general structure [NH4P03] . There are two main families of ammonium polyphosphate as shown below  

Monomer units in chain (n) pH Solubility in water (g/IOOmI) Median particle size (pm) 

Crystal-phase I APP (APP I) is characterized by a variable linear chain length, showing a lower decomposition temperature (approximately 150 °C) and a higher water solubility than crystal phase II (APP II). APP II has a cross-linked and branched structure. The molecular weight is much higher than that of APP I with n 1000. APP 11 has a higher thermal stability and lower water solubility than AP PI (see Tables 17.9 and 17.10). 

APP is a stable, nonvolatile material. It slowly hydrolyzes in contact with water to produce monoammonium phosphate (orthophosphate). This process is autocatalytic and is accelerated by higher temperatures and prolonged exposure to water. The decomposition temperature of APP is related to the length of the polymer chain. Long-chain APP starts to decompose at temperatures above 300 °C to polyphosphoric add and ammonia. Short-chain APP, defined as that having a chain length below 100 monomer units, begins to decompose at temperatures above 150°C. 

APP and APP-based systems are very effident halogen-free flame retardants mainly used in polyolefins (PE, PP), epoxies, polyurethanes, unsaturated polyesters, phenolic resins, and others. APP is a nontoxic, environment friendly material and it does not generate additional quantities of smoke due to intumescence. Compared to other halogen-free systems, APP requires lower loadings. In thermoplastic formulations, APP exhibits good processability, retention of good mechanical properties. 

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Insoluble Ammonium Polyphosphate. When ammonium phosphates are heated ia the presence of urea (qv), or by themselves under ammonia pressure, relatively water-iasoluble ammonium polyphosphate [68333-79-9] is produced (49). There are several crystal forms and the commercial products, avaUable from Monsanto, Albright WUson, or Hoechst-Celanese, differ ia molecular weight, particle size, solubUity, and surface coating. Insoluble ammonium polyphosphate consists of long chains of repeating 0P(0)(0NH units. 

A series of compounded flame retardants, based on finely divided insoluble ammonium polyphosphate together with char-forming nitrogenous resins, has been developed for thermoplastics (52—58). These compounds are particularly useful as iatumescent flame-retardant additives for polyolefins, ethylene—vinyl acetate, and urethane elastomers (qv). The char-forming resin can be, for example, an ethyleneurea—formaldehyde condensation polymer, a hydroxyethylisocyanurate, or a piperazine—triazine resin. 

A newer self-intumescent phosphoric acid salt has been introduced by Albright WHson as Amgard EDAP, mainly as an additive for polyolefins. It is a finely divided soHd, mp 250°C, having a reported phosphoms content of 63 wt % as H PO. It appears to be the ethylenediamine salt of phosphoric acid (1 1). Unlike ammonium polyphosphate, it does not require a char-forming synergist (62). 

A bicychc pentaerythritol phosphate, CN-1197, has more recently been introduced by Great Lakes Chemical for use in thermosets, preferably in combination with melamine or ammonium polyphosphate (89). It is a high melting soHd befleved to have the following stmcture [5301-78-0] (87) ... 

Related esters of this alcohol are disclosed by Ak2o as useflil flame retardants for polypropylene, particularly in combination with ammonium polyphosphate (90). 

Usage of phosphoms-based flame retardants for 1994 in the United States has been projected to be 150 million (168). The largest volume use maybe in plasticized vinyl. Other use areas for phosphoms flame retardants are flexible urethane foams, polyester resins and other thermoset resins, adhesives, textiles, polycarbonate—ABS blends, and some other thermoplastics. Development efforts are well advanced to find appHcations for phosphoms flame retardants, especially ammonium polyphosphate combinations, in polyolefins, and red phosphoms in nylons. Interest is strong in finding phosphoms-based alternatives to those halogen-containing systems which have encountered environmental opposition, especially in Europe. 

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. 

Those based on the reaction between magnesium oxide and ammonium polyphosphate (APP) (Sugama Kukacka, 1983b). 

Sugama Kukacka (1983b) described cements based on magnesium oxide and a 56% aqueous solution of ammonium polyphosphate (APP). The po wder was a fine magnesium oxide that had been calcined above 1300 °C and had a surface area of 1 to 5 m g . The reaction was strongly exothermic the cements set within 3 minutes and developed an early strength of 13-8 MPa after 1 hour and over 20 MPa after 5 hours. 

Sugama, T. Kukacka, L. E. (1983b). Characteristics of magnesium polyphosphate cements derived from ammonium polyphosphate solutions. Cement Concrete Research, 13, 499-506. 

Adriano D.L., Murphy L.S. Effects of ammonium polyphosphates on yield and chemical composition of irrigated com. Agron J 1970 62 561-567. 

Moreover, simultaneous evolution of water implies that condensation of melamine is combined with that of polyphosphoric structures. Assuming the reaction scheme proposed above, melam polyphosphate and ammonium polyphosphate groups should be formed from melamine polyphosphate ... 

It is known that ammonium polyphosphate tends to dissociate liberating ammonia above 300 C and the resulting free hydroxy groups condense giving crosslinked structures (ultraphosphate) with elimination of water (28.29) ... 

M. LeBras., Mineral fillers in intumescent fire retardant formulations - Criteria for the choice of a natural clay filler for the ammonium polyphosphate/pentaeythritol/polypropylene system, Fire and Materials, vol. 20, pp. 39-49,1996. 

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

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. ... 

In remote reservoirs not affected by anthropogenic pollution, particle trapping can reduce the available nutrients. In the Canadian Rocky Mountains, fertihzer has been added to lakes and rivers in the form of liquid ammonium polyphosphate with the goal to stabihze nutrient concentration at historical levels [5]. 

Significant changes in the distribution of the products of pyrolysis were observed with the flame retardants mentioned above. This indicates that the polyphosphoric residue of ammonium polyphosphate modifies the mechanisms of the thermal decomposition of these polymers. 

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... 

A majority of the fasteners used in automobiles in the U.S. are coaled with microcapsitles loaded with an adhesive. Other uses include encapsulated ammonium polyphosphate incorporated in plashes that acts as a hre-rctardant and microencapsulated oil-held chemicals for use hv the oil industry. 

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. 

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