Requirements for flame retardants

Tris(2,3-dibromopropyl)phosphate (Tris), used to treat children s sleepwear to reduce flammability, was banned from use. The chemical was linked to kidney cancer in mice and rats and was mutagenic in bacteria. At the time it was used on 40-60% of children s sleepwear, mostly polyester, to enable it to meet federal requirements for flame retardance. 

After PVC, polyolefin copolymers, predominantly polyethylene copolymers, are the next most widely used material for FR applications in wire and cable. Polyethylenes have very good dielectric strength, volume resistivity, mechanical strength, low temperature flexibility, and water resistance. In contrast to PVC, polyolefins are not inherently FR and thus are more highly formulated, requiring the addition of FRs to meet market requirements for flame retardancy. For this reason, and because of the steady global trend toward halogen-free materials for wire and cable applications, more space will be devoted to this section on FR polyolefins compared with the above discussion of PVC. 

Horrocks AR. Regulatory and testing requirements for flame retardant textile applications. In Alongi J, Horrocks AR, Carosios F, Malucelli G, editors. Update on flame retardant... 

UL 94 is used to measure burning rate and characteristics based on standard samples. The ratings are HB, V-2, V-1 and V-0. HB means that once ignited the sample will continue to bum but at a controlled rate. V-0 is the best rating and is often required for flame retarded pol3rmers in many sectors. PP is HB. 

The requirement for fire retardance in many applications has never been greater. Not only is the requirement for flame retardance increasing, but the control of airborne byproducts has become more important. In small-scale fires, it may be sufficient for a product to be self-extinguishing. There are, however, in the modern building, ship, train... 

In choosing a flame retardant, consideration must be given to the impact on the performance of the resin system and the finished base material. These materials, at the levels required for flame retardancy, can affect the physical properties of the laminate, change rheological properties, and alter cure kinetics of the resin system. Generally, the reactive compounds are preferred since they are bound to the polymer backbone, which prevents release into the environment, and, in comparison to additives or fillers, they seem better suited to obtaining the desired material properties. Table 7.2 summarizes some of the available halogen-free flame retardants. 

Silicone rubber insulated cables have been developed which meet the stringent requirements of the lEC 331 specification, including the all important 3 h flame test. In this test the cable is required to function for 3 h at working voltage in a gas flame of 750 °C. In addition, silicone cable is available which meets BS4066 and IEC332 requirements for flame retardant cables. Silicone rubber also has a low calorific value (3 8 kcal/g) which when combined with the other features described above makes it a natural choice for cable insulation in many other applications. 

Sodium hydroxide is the alkali usually used in conjunction with dithionite. Sodium carbonate is a possible alternative when Cl Solubilised Sulphur dyes are used but is insufficiently alkaline for the Cl Sulphur brands, requiring careful control if over-reduction and the associated lower yields are to be avoided [30]. Typical concentrations are given in Table 12.24. The system of sodium carbonate and sodium dithionite used to reduce blue and black Cl Solubilised Sulphur dyes is particularly suitable for flame-retardant viscose fibres that are sensitive to strong alkalis, since it preserves a satisfactory level of flame retardancy [30]. It is also possible to use a mixture of dithionite with sodium sulphide in alkaline media. 

The development of the different methods for the production of flame retardant grade magnesium hydroxide has recently been reviewed [100]. Although not a common mineral, there are some workable deposits of brucite, especially in the US and China and product obtained by milling high purity brucite deposits is being marketed, but has so far made little impact. This is probably because the high levels needed for flame retardancy can only be tolerated if the particle size and shape are carefully controlled and this requires the use of synthetic methods of production. 

With all the changes underway for flame-retardant technology, sustainability requirements for polymeric materials, and ever-changing fire risk scenarios, it can be quite hard to predict what the future of flame retardancy will be, but there are some trends and information that allow us to make some suggestions about the future. So, our predictions for the future are the following ... 

Flame Retardants. Because PVC contains nearly half its weight of chlorine, it is inherently flame-retardant. Not only is chlorine not a fuel, but it acts chemically to inhibit the fast oxidation in the gas phase in a flame. When PVC is diluted with combustible materials, the compound combustibility is also increased. For example, plasticized PVC with > 30% plasticizer may require a flame retardant such as antimony oxide, a phosphate-type plasticizer, or chlorinated or brominated hydrocarbons (145,146). 

The increasing demand for FR PVC-U applications has prompted work in this area. The use of functional fillers can cause a dramatic deterioration of physical properties at the addition levels necessary to achieve the requirements of flame retardancy and smoke emission. An evaluation has shown zinc hydroxystannate to give the best overall FR and SS characteristics without adversely influencing important physical properties (129). The addition of low levels of zinc borate and/or ATH was noted to improve flame retardancy and reduce smoke density in a PVC-U formulation (265). 

Many tests and methods have been developed to study flammability, but only those which are important for flame-retardant styrenic polymers will be considered here. Some of these tests are regulatory requirements for specific applications, while others are more for research purposes. The flame retarding of styrenic polymers is often done to pass a specific test, and the formulation needed to pass one test may be completely different to that required for another test. 

Flame-retardant finishes provide textiles with an important performance characteristic. Protection of consumers from unsafe apparel is only one area where flame retardancy is needed. Firefighters and emergency personnel require protection from flames as they go about their duties. Floor coverings, upholstery and drapery also need protection, especially when used in public buildings. The military and the airline industry have multiple needs for flame-retardant textiles. 

The toxicity of some flame-retardant components and of their combustion gases is a particular concern for flame-retardant finishes, especially if based on halogens and several heavy metals. Therefore, aircraft textile equipment has to fulfil special requirements, for example, smoke density and toxicity tests. Toxicity problems include ... 

PROPERTIES REQUIRED OF MAGNESIUM HYDROXIDE FOR FLAME-RETARDANT APPLICATIONS... 

Wool has been regarded as a relatively safe fiber from the flammability point of view. However, it could be flame retarded to a higher degree if required. Hendrix et al. (26) suggested a large improvement in fire resistance of wool by treatment with 15% H PO. Beck et al. (27) showed that weak acidic materials, such as boric acid and dihydrogen phosphate, are effective additives for flame retarding wool by the condensed-phase mechanism (increased char residue). 

This listing of chain extenders or cross-linkers is obviously incomplete since many other types of chain extenders may be used where special end use requirements may have to be met, for example, for flame retardance. In this case, halogenated diols, for example, 2,3-dibromo-2-butane-l,4-diol (GAF Corp.), or phosphate or phosphonate group-containing diols, for example, Fyrol 6 (Stauffer Chemical Co.), may be used. 

Chem. Descrip. Ethylene-vinyl chloride copolymer latex Uses Coating binder and saturant for paper and paperboard applies. binder for flame retardant fabrics, heat sealable nonvirovens useful in heat seal adhesive appiics. or where a moisture barrier is required binder for nonwovens and textiles imparts flexibility and water resist, to caulks, mastics, barrier coats in building applies., low MTVR coalings Features Inherently flame retardant... 

What are the current trends and innovations First of all, demand for flame retardants will rise worldwide on account of stricter fire-safety levels. It will be spurred on inter alia by the harmonisation of fire protection requirements for products in the constmction industry and for railway rolling stock within Europe, as well as through the introduction and implementation of fire regulations in newly industrialised countries, especially in Asia, with particular focus on China. The 42V power supply in cars and UL94 V-0 television sets in Europe will similarly contribute towards this trend. Over the medium term, US fire safety requirements could be imposed on upholstered furniture in the private sphere throughout the entire country, which would ensure a boom in the demand for flame retardants. 

Of particular importance is the SBI test, which will be used to test building products in future. In many cases, the fire safety requirements imposed on combustible materials will be more stringent than those of existing national tests, a fact that should well lead to greater demand for flame retardants of one sort or another. 

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