Phosphorus flame retardants development

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. 

Weil, E. D., Recent developments in phosphorus flame retardants, Proceedings of 3rd Beijing International Symposium on Flame Retardants and Flame Retardant Materials, 1999, Beijing, China, pp. 177-183. 

In a joint ventnre, DuPont-Toray, Ichimura Sangyo and Takayasu have announced the development of a new manufactnring process for flame retardant resins which avoids the need for snch additives as organic phosphorus flame retardants. Instead the flame retardant properties are obtained by adding... 

Red Phosphorus. This aHotropic form of phosphoms is relatively nontoxic and, unlike white phosphoms, is not spontaneously flammable. Red phosphoms is, however, easily ignited. It is a polymeric form of phosphoms having thermal stabiUty up to ca 450°C. In finely divided form it has been found to be a powerful flame-retardant additive (26,45—47). In Europe, it has found commercial use ia molded nylon electrical parts ia a coated and stabilized form. Handling hazards and color have deterred broad usage. The development of a series of masterbatches by Albright Wilson should facihtate further use. 

Phosphorus-Containing Diols and Polyols. The commercial development of several phosphoms-contaiuing diols occurred in response to the need to flame retard rigid urethane foam insulation used in transportation and constmction. There are a large number of references to phosphoms polyols (111) but only a few of these have been used commercially. 

TBBA, a brominated flame retardant, is used in the epoxy resin laminate in printed circuit boards in most manufacturers products. In 1997, a phosphorus-based alternative to TBBA was developed by the German engineering giant, Siemens,... 

In 2000, NEC developed an epoxy resin with what it describes as a fire-retardant structure that avoids the need for either TBBA or phosphorus-based flame retardants in circuit boards. The new resin contains a metal hydroxide retardant. The company claims the new board is almost totally free of pollutants, and is easy to process and thermally recycle. By also integrating flame retardant properties within the board, use of the metal hydroxide is minimised, while offering good electrical properties, higher heat resistance and improved processing characteristics. ... 

Two examples have been selected to demonstrate this process. The first involves a selective catalysts development program at Akzo Nobel under collaboration with Mark E. Davis of the California Institute of Technology (Caltech). Catalysts with greater selectivity were needed to improve the performance of a product line of phosphorus-based flame retardants and functional fluids. The Akzo Nobel... 

Several commercial products have resulted from our phosphorus oligomer research. Fyrol 99, a 2-chloroethyl ethylene phosphate oligomer, has been successfully used as a flame retardant additive in rebonded urethane foam, in thermoset resins, in intumes-cent coatings, adhesives, paper air filters (13), and related uses. This product is less volatile and has a higher flame retardant efficacy than the parent compound tris(2-chloroethyl) phosphate. A related product was developed especially for use in flexible polyurethane foams. A vinylphosphonate/methylphospho-... 

The major developments in reactive phosphorus-based flame retardants for epoxy resins to 2005 have been well reviewed.52 It will suffice here, therefore, to outline just the major developments and to highlight the most recent work. 

The use of phosphorus-based flame retardants in combination with other, better established, flame retardants is most effective in situations in which the combination proves synergistic. However, as yet our understanding of such synergistic effects is far from complete and more fundamental work is required in this area Work in which the gaseous and solid products of combustion, with and without the presence of flame retardants, are carefully analyzed. Such analyses can now be undertaken more readily than in the past, owing to the relatively recent development of techniques such as gas-phase FT-infrared spectroscopy and laser-pyrolysis time-of-flight mass spectrometry for the identification of volatiles, and solid-state NMR spectroscopy and x-ray photoelectron spectroscopy for the analysis of chars. 

Whereas UL 94 delivers only a classification based on a pass-and-fail system, LOI can be used to rank and compare the flammability behavior of different materials. In Figure 15.2 the increasing LOI values are presented for different polymers as an example POM = poly(oxymethylene), PEO = poly(ethyl oxide), PMMA = poly(methyl methacrylate), PE = polyethylene), PP, ABS, PS, PET = polyethylene terephthalate), PVA = poly(vinyl alcohol), PBT, PA = poly(amide), PC, PPO = poly(phenylene oxide), PSU, PEEK = poly(ether ether ketone), PAEK = poly(aryl ether ketone), PES, PBI = poly(benzimidazole), PEI = poly(ether imide), PVC = poly(vinyl chloride), PBO = poly(aryl ether benzoxazole), PTFE. The higher the LOI, the better is the intrinsic flame retardancy. Apart from rigid PVC, nearly all commodity and technical polymers are flammable. Only a few high-performance polymers are self-extinguishing. Table 15.1 shows an example of how the LOI is used in the development of flame-retarded materials. The flame retardant red phosphorus (Pred) increases... 

A flame retarded rigid PU foam needs around 20-25% chlorine or 5-6% bromine or 1.5-2% phosphorus [1, 2, 4, 11]. During the history of PU many reactive flame retardants were developed, but only a few are used effectively in practice. 

Thermoplastics. Many flame-retardant chemicals have been developed for use in thermoplastics. Most of these flame retardants are of the additive type, usually halogen- and/or phosphorus-based compounds. 

Finally, to conclude, it is also important to point out that phosphorus-based poly(meth)acrylates are successfully employed for many applications, including flame retardancy, anticorrosion, and in the biomedical field. As these applications are of great interest, we can assume that the development of other phosphorus-based (meth)acrylate monomers will continue in the future. 

The active species in fire retarding are the halogens, chlorine and bromine, phosphorus, and water. The performance of these primary flame retardants is enhanced by synergists antimony, zinc and other metal salts. Some help to develop a protective char (e.g., phosphorus-based systems), separating the unbumed polymer from the flame and heat source. 

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