Examples of flame retardants

Table 3.15 Examples of flame-retardant grade properties...

Condensed phase. In condensed-phase modification, the flame retardant alters the decomposition chemistry so that the transformation of the polymer to a char residue is favored. This result could be achieved with additives that catalyze char rather than flammable product formation or by designing polymer structures that favor char formation. Carbonization, which occurs at the cost of flammable product formation, also shields the residual substrate by interfering with the access of heat and oxygen. Phosphorus-based additives are typical examples of flame retardants that could act by a condensed phase mechanism. 

Since only two examples of flame retardant systems are currently available, it seems that the technology is still in its commercial infancy. However, even with the significant improvements in properties brought by polymer nanocom-posite technology, it is not always a drop-in replacement for existing materials. Further, there are times when it does not make sense to use a polymer nanocom-posite for these applications, especially when the existing material is far less... 

Other examples of flame retardant applications include incorporation of N3P3CI6 in a fiber-reinforced poly(benzoxazine-co-E-caprolactam) and modified cyclophosphazenes containing a phosphaphenanthrene end groups. ... 

Although phosphine [7803-51-2] was discovered over 200 years ago ia 1783 by the French chemist Gingembre, derivatives of this toxic and pyrophoric gas were not manufactured on an industrial scale until the mid- to late 1970s. Commercial production was only possible after the development of practical, economic processes for phosphine manufacture which were patented in 1961 (1) and 1962 (2). This article describes both of these processes briefly but more focus is given to the preparation of a number of novel phosphine derivatives used in a wide variety of important commercial appHcations, for example, as flame retardants (qv), flotation collectors, biocides, solvent extraction reagents, phase-transfer catalysts, and uv photoinitiators. 

However this solution is not always convenient and may prevent high productivity and/or the production of intricate forms which require high temperature processing. Fortunately, some fire retardants dramatically increase the flowability of fire retardant plastics melts. For example ABS, flame retarded with F-2016 or F-2016M (brominated epoxy) has much higher flowability, melt flow index (MFI), and spiral flow index, than virgin ABS (Fig. 1). 

Let us consider the use of flame retardants in furniture, which has been a standard additive approximately since the 1970s. Flame retardants are added to reduce flammability and therefore to prevent fire. In Sweden there should be some 6 million couches which we will use for this simple example. Each couch needs some 0.5 kg of flame retardant. 

As is seen, this example shows that flame retardants might be good for society (from a socio-economic perspective) even if they cause a number of adverse environmental and human health impacts as long as the value of the avoided mortality impacts is larger. Replacement of flame retardants should only be done (from an economic perspective) if the replacement cost is smaller than the avoided environmental and human health values. 

A significant advantage to performing well with a wide range of flame retardants is formulating flexibility. There are many factors which limit the choice of flame retardants asided from flame retardant performance and compatability. For example, environmental constraints (no antimony to the sewer, no ammonia in the workplace) and compatability constraints (shorter than normal shelf life with certain emulsions) may limit the choice. 

Blends of flame retardant additives have been advocated as an approach to an optimum balance of properties in the finished products. For example, blends of tetrabromophthalate esters with de-cabromodiphenyl oxide or other flame retardants are reported to yield a V-0 rating in modified PPO and in polycarbonate resins without compromising melt processability or performance properties (23a-b). 

Recent developments in the field of flame retardants have been reviewed (27). A combination of flame retardants with other properties, such as antioxidants have been developed. An example of such a compound is shown in Figure 9.4. 

It has been reported that the effectiveness of copolymerized DOPO-type monomers can be further improved if the alcohol-amine derivatives of DOPO, for example, Structure 5.11, are used rather than similar structures not containing nitrogen.30 Of the FR fibers based on P-containing comonomers, it has been found that those based on Structure 5.10 are more hydrolytically stable, presumably because the P-containing group is in a cyclic structure and also should the hydrolysis of the P-0 bond occur, it will not lead automatically to a marked reduction in molecular weight.31 All the P-modified PETs appear to be subject to both the vapor-and condensed-phase mechanisms of flame retardance, with the former predominating.32 33... 

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... 

Figures 15.8 and 15.9 illustrate examples of how cone calorimeter data can be used in the development of flame-retarded materials. PA 66-GF without Pred showed typical fire behavior for noncharring polymers containing inorganic glass fiber as inert filler,69 when high external heat flux is applied. The shape of the HRR curve is divided in two different parts. In the beginning, the surface layer pyrolysis shows a sharp peak, followed by a reduced pyrolysis rate when the pyrolysis zone is covered by the glass fiber network residue layer. When Pred was added, the PA 66-GF samples were transformed into carbonaceous char-forming materials, which led to a...

Polyolefin (PO) foams are tough, flexible, and resistant to chemical and abrasion however, they are characterized by a low inherent fire resistance and hence quite high amounts of flame-retardants are needed to fulfill fire safety requirements. Therefore, when fire requirements are stringent, generally styrene and engineered plastics are used in spite of polyolefin foams because, for example, for complying UL 94 V-0 rating, 30%-40% fire retardant is normally required for PO foams while only 10%-20% FR additives are required for styrenic foams.91... 

The mechanism of action of flame retardants in thermoplastic materials (polyethylene, polypropylene, polystyrene, cellulosics, PMMA, etc.) is unknown and is certainly quite complex. Broido (7) presented a good example in the difficulties of explaining how fire retardants work. He found that materials which were most effective in preventing flaming combustion of cellulose were also effective in causing sugar cubes to support flame ... 

Other types of finishes typically reduce the main effect of a finish type, for example the flame retardant effect is decreased by nearly all other types of chemical finishes as they add flammable components to the fabric. 

Fortunately true antagonistic effects are rare, but true synergistic effects are also rare, where the resnlting effect of a combination is greater than the sum of the single effects of the combined products. Examples of both cases are different types of flame retardants. 

Because reactive types of flame retardants are polymer-specific, their application is limited. There are several reactive flame retardants, specifically produced and all different in composition. For example, there is a 25% pelletized concentrate of antimony pentoxide, bromine and polypropylene resin of various melt flow indices, which is geared to PP fibers for textiles and carpets,... 

In the case of flame retardant silicone elastomer, many ingredients such as silica, platinum, and other flame retardant agents are incorporated into the base siloxane polymer. But there is no need to use the halogenated flame retardant agent, for example, bromine or chlorine compounds. This difference is an advantage of silicones compared with other synthetic polymers in terms of health and safety. 

The EU directives may also motivate manufacturers to work toward the elimination of other substances, besides those banned under RoHS, in the products they make. For example, electronics manufacturers, because they are now required to take back their products and meet recycling targets set by the WEEE Directive, may want to eliminate other chemicals (such as other types of flame retardant) that create impediments to recycling or pose risks to their workers health. 

In just 17 years, the entire field of flame retardancy has taken a giant leap forward and the technology to provide FR synthetic materials has made remarkable progress. Today, flame retardant grades of synthetic polymers have found applications in areas considered impossible a few years ago. One example is the use of polyurethane foam in upholstered furniture for high-risk occupancies such as hotels, prisons and hospitals. Polyurethane foam, which was once described in the press as "solid gasoline" is now formulated to withstand severe fire test exposure without propagating the fire. 

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