Phosphorus-based retardants

Substance TBBA replaces PBB/PBDE Polymerized TBBA Phosphorus-based retardants Mineral-based retardants Change base material Separate high and low voltage Reduce voltage... 

Phosphorus-based retardants possess the second largest market [1] and comprise a large number of forms associated with different mechanisms. Among these, a basic mechanism is achieved through the reactions between chemicals produced... 

With special synergists, a protective coating in the form of an intumescent layer can be formed in case of flaming, and phosphorus FRs are also good suppressors of afterglow and smoke. These properties make phosphorus-based retardants of particular interest in gel coats. 

The mode of action of phosphorus-based flame retardants is believed to take place in either the condensed or the vapor phase (refs. 1,2) depending on the type of phosphorus compound and the chemical composition of the polymer. Phosphorus has been reported to be 3 to 8 times more effective than bromine depending on the polymer type (ref. 3). 

When used purely as an insulator, foam densities can be as low as 0.02 to 0.08 g/cm3. In structural applications the foam s density can rise to 0.4 to 0.7 g/cm3. The use of fluorocarbons as blowing agents has largely given way to more environmentally friendly agents, such as low molecular weight hydrocarbons. We can impart flame retardancy by incorporating chlorine-or phosphorus-based compounds. 

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. ... 

The early patent disclosures have claimed the application of a wide spectrum of gas-evolving ingredients and phosphorus-based organic molecules as flame retarding additives in the electrolytes. Pyrocarbonates and phosphate esters were typical examples of such compounds. The former have a strong tendency to release CO2, which hopefully could serve as both flame suppressant and SEI formation additive, while the latter represent the major candidates that have been well-known to the polymer material and fireproofing industries.The electrochemical properties of these flame retardants in lithium ion environments were not described in these disclosures, but a close correlation was established between the low flammability and low reactivity toward metallic lithium electrodes for some of these compounds. Further research published later confirmed that any reduction of flammability almost always leads to an improvement in thermal stability on a graphitic anode or metal oxide cathode. 

Figure 75. Flammability of the electrolytes containing various phosphorus-based flame retardants (FR). All electrolytes are composed of these flame retardants in 1.0 m LiPFe/EC/EMC. (Reproduced with permission from ref 529 (Eigure 1). Copyright 2003 The Electrochemical Society.)...

Condensed-Phase Mechanisms. The mode of action of phosphorus-based flame retardants in cellulnsic sy stems is probably best understood. Cellulose decomposes by a noncalalyzed route lo tarry depolymerization products, notably levoglucosan, which then decomposes to volatile combustible fragments such as alcohols, aldehydes, ketones, and hydrocarbons. However, when catalyzed by acids, the decomposition of cellulose proceeds primarily as an endothermic dehydration of the carbohydrate to water vapor and char. Phosphoric acid is particularly efficaceous in this catalytic role because of its low volatility (see Phosphoric Acids and Phosphales). Also, when strongly heated, phosphoric acid yields polyphosphoric acid which is even more effective in catalyzing the cellulose dehydration reaction. The flame-retardanl action is believed to proceed by way of initial phosphory lation of the cellulose. 

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. 

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... 

The addition of phosphorous-based plasticizers will provide a degree of fire retardancy to the polyurethane. Fryol PCF and CEF have been used in polyurethane systems. Most phosphorus-based fire retardants are thin liquids that are compatible with polyurethanes. Because of the very varied nature of fire-resistant tests, the material made must be tested to the appropriate standard. 

Phosphorus-Based Inorganic Additive Flame Retardants.109... 

PHOSPHORUS-BASED INORGANIC ADDITIVE FLAME RETARDANTS... 

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. 

Levchik, S. V. and Weil, E. D., A review of recent progress in phosphorus-based flame retardants, J. Fire... 

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. 

Chigwada, G., Jash, P., Jiang D.D., and Wilkie, C.A. 2005. Fire retardancy of vinyl ester nanocomposites Synergy with phosphorus-based fire retardants. Polym. Deg. Stab. 89 85-100. 

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