Phosphorus-bromine flame retardant

Phosphorus -bromine flame retardant synergy was demonstrated in a 2/1 polycarbonate/polyethylene blend. These data also show phosphorus to be about ten times more effective than bromine in this blend. Brominated phosphates, where both bromine and phosphorus are in the same molecule, were also studied. In at least one case, synergy is further enhanced when both phosphorus and bromine are in the same molecule as compared with a physical blend of a phosphorus and a bromine compound. On a weight basis, phosphorus and bromine in the same molecule are perhaps the most efficient flame retardant combination. The effect of adding an impact modifier was also shown. 

Green, J., A phosphorus-bromine flame-retardant for engineering thermoplastics A review, J. Fire Sci., 1994, 12, 38-408. 

Squires [49] investigated the use of melt blendable phosphorus/bromine flame-retardants in PP woven and non-woven fabrics and carpets. Consistent high quality injection moulded parts met V2 ratings in the UL 94 test. Good results are easily achieved with minimal fire retardant loading or the use of a synergist. 

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). 

Table 1. Oxygen Index of PET Fibers Containing Phosphorus or Bromine Flame Retardants ...

Table 2. Enhancement of Bromine Flame Retardancy by Antimony and Phosphorus in a PET Fiberl... 

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,... 

ENDS Report 308, September 2000. NEC unveils circuit boards free of halogen or phosphorus compounds ENDS Report 308, September 2000. NEC unveils circuit boards free of halogen or phosphorus compounds Personal communication with Magnus Bjork, IKEA, at Brominated Flame Retardants and Foam Furniture Conference and Roundtable EPA 9. San Francisco, April 2003 Personal communication with HP, H M, Boots and Sainsbury, May-June 2003 Skanska (2004) Press release from Johan Gerklev, Environmental Manager, Skanska Sweden, December 12004 Skanska (2002). Brandforsk project 706-021. See www.skanska.se UBA (2003). Precautionary Risk... 

The term brominated flame retardant (BFR) incorporates more than 175 different types of substances, which form the largest class of flame retardants other classes are phosphorus-containing, nitrogen-containing, and inorganic flame retardants (Bimbaum and Sttaskal 2004). The major BFR substances in use today (depicted in Fig. 4.6) are tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and mixtures of polybrominated diphenyl ethers (PBDEs) (namely, deca-bromodiphenyl ether (DBDE), octabromodiphenyl ether (OBDE), and pentabro-modiphenyl ether (pentaBDE)). 

The major brominated flame retardant used with epoxy resins is TBBA. This is a reactive halogenated intermediate incorporated during resin preparation. However, other bromine containing species plus phosphorus containing monomers or curing agents may be reacted with the main epoxy resin eomponents during polymerisation. The latter may be alkyl or aryl phosphates. The best appear to be phenyl phosphate derivatives. 

Dow has produced a polycarbonate grade for liquid crystal display monitors, incorporating a silicone flame retardant. Formulations containing the silicone additive are said to have better impact strength and temperature resistance than those protected by phosphorus based flame retardants, and better heat and light stability than those containing brominated FRs. 

Albemarle s combined net sales rose from US 941 M in 2000 to US 1110 M in 2003, despite very difficult trading conditions. Net income fell in the same period from US 102 M to US 72 M, and long-term debt rose from US 97 M to US 228 M These figures are partly explained by the fact that several acquisitions have been made. They included Akzo Nobel s refinery catalysts, the Korean distributor Taerim, Arkema s fine chemicals bromine business, Rhodia s phosphorus based flame retardants business for polyurethanes, the fuel and lubricant antioxidants business of Ethyl, the fine chemicals business of ChemEirst, and Martinswerk. 

Phosphorus containing flame retardants are used as phosphates, phosphonates, phosphines and phosphinic oxides. Halogen-containing phosphate esters such as bromine and chlorine in the form of tris (halogen alkyl) phosphates are popular [33]. The effects of phosphorus and brominated additives on flexible PU foam were compared [179]. Melamine has broad utility as a flame retardant additive in flexible PU foams [180]. 

For more than a decade potential environmental problems associated with organo-bromine flame retardant systems have motivated the search for non-halogen-based approaches to reduce polymer flammability. Initially, research focused on development of new phosphorus-based flame retardants, and numerous publications and patents have been issued in this area. Similarly motivated research has also produced nonhalogen flame retardant approaches based on other elements, such as boron and sihcon. At the same time, work on the use of additives, or flllers, with nanometer-scale primary particle sizes, produced polymer nanocomposites. These materials exhibit enhancement in a variety of physical properties at one-tenth the loading required when micrometer-size additives are used. ... 

With a recent push toward non-brominated flame retardants, phosphorus-based alternatives, such as phosphate esters, are used more frequently for various applications. Their use as plasticizers is also well known. However, their function as environmental stress crack agents of various thermoplastics is less well recognized. Two case studies, one - in which a triaryl phosphate was a component of the formulation, the other - in which it was migrating from an adjacent component illustrate some of the problems with their use. Fractographic analysis and various analytical techniques were used to determine a root cause of each of the two failures. 

Reduction in flammability is achieved by the incorporation of flame retardants into the polymer. Two possible approaches to this are available either the use of additives blended into the polymer at processing stage (additive type) or the use of alternative monomers which confer reduced flammability on the final product (reactive type). A number of elements have been found to assist with conferring flame retardancy on polymers, the main ones being bromine, chlorine, nitrogen, and phosphorus. 

Phosphorus/bromine combinations are perhaps the most effective flame retardant combination (ref. 3) and claims have been made for synergy. The formation of phosphorus trichloride or oxychloride has been postulated by analogy to that of the formation of antimony trichloride and oxychloride but there is no evidence for this mechanism. Some reports of synergy appear to be a result of a nonlinear response to the flame retardant concentration. 

A mixture of bromine and phosphorus compounds was shown to be more effective in ABS resin than anticipated by the results obtained with the individual flame retardants. When bromine and phosphorus are in the same compound even higher oxygen indices were obtained. The data convincingly shows... 

Convincing evidence for phosphorus/bromine synergy has now been found in a 2/1 polycarbonate/polyethylene terephthalate blend. Phosphorus and bromine blends were studied as well as compounds which have both elements in the same compound. The relative flame retardant efficiencies of phosphorus and bromine are also reported. 

A 2/1 blend of polycarbonate and polyethylene terephthalate (PC/PET) was flame retarded with bromine, phosphorus, a blend of bromine and phosphorus, and compounds containing both phosphorus and bromine in the same molecule. All compositions contained 0.5 % Teflon 6C as a drip inhibitor and where specified 5 % of an impact modifier. 

In Figure 3 where the BrPC and TPP are compared, the bromine concentration increases from left to right and the phosphorus concentration increases from right to left. The two curves intersect at 5 % bromine and 0.5 % phosphorus, indicating that phosphorus is ten times more effective as a flame retardant. At the extremes 1 % phosphorus is equivalent to about 9 + % bromine. 

Commercially available flame retardants include chlorine- and bromine-containing compounds, phosphate esters, and chloroalkyl phosphates. Recent entry into the market place is a blend of an aromatic bromine compound and a phosphate ester (DE-60F Special) for use in flexible polyurethane foam (8). This paper describes the use of a brominated aromatic phosphate ester, where the bromine and phosphorus are in the same molecule, in high temperature thermoplastic applications. 

Three flame retardants were compared in this study, namely, a brominated polycarbonate oligomer (58% bromine), a brominated polystyrene (68% bromine), and a brominated triaryl phosphate ester (60% bromine plus 4% phosphorus). These are described in Table I. Figures 1 and 2 compare the thermal stability of the brominated phosphate with commercial bromine-containing flame retardants by thermogravimetric analysis (TGA) and by differential scanning calorimetry (DSC). The brominated phosphate melts at 110°C and shows a 1% weight loss at 300°C. Brominated polycarbonate and brominated polystyrene are polymeric and are not as volatile at elevated temperatures as the monomeric flame retardants. 

Flame retardants, 11 447-454, 459-479. See also Fire retardant entries Halogenated flame retardants Phosphorus flame retardants antimony compounds in, 3 54 brominated and chlorinated additive, 11 461-470... 

Generally, flame retardants for engineering PET compositions are based on bromine-containing compounds (such as brominated polycarbonate, decabro-modiphenyl oxide, brominated acrylic, brominated polystyrene, etc.). Such compounds are available commercially (such as from the Ethyl Chemical Corporation, Great Lakes Chemical Corporation, Dead Sea Bromine Company, etc.) In addition, the flame-retardant package generally contains a synergist, typically sodium antimonate. PET may also be flame-retarded with diarylphosphonate, melamine cyanurate or red phosphorus. 

Flame Retardants. Bromine compounds make up an important segment of the market for flame retardants used in polymers. Additive flame retardants are added to polymers during processing reactive flame retardants react chemically to become part of the polymer chain itself In addition to the compounds listed in Table 3, a number of proprietary mixtures and phosphorus—bromine-containing flame retardants are also sold (see Flame retardants, HALOGENATED, FLAME RETARDANTS). 

---