Flame retardant compounds intumescent

Protective Coatings. Some flame retardants function by forming a protective Hquid or char barrier. These minimize transpiration of polymer degradation products to the flame front and/or act as an insulating layer to reduce the heat transfer from the flame to the polymer. Phosphoms compounds that decompose to give phosphoric acid and intumescent systems are examples of this category (see Flame retardants, phosphorus flame retardants). 

Ammonium polyphosphates, on the other hand, are relatively water insoluble, nonmelting solids with very high phosphorus contents (up to about 30%). There are several crystalline forms and the commercial products differ in molecular weights, particle sizes, solubilities, and so on. They are also widely used as components of intumescent paints and mastics where they function as the acid catalyst (i.e., by producing phosphoric acid upon decomposition). They are used in paints with pentaerythritol (or with a derivative of pentaerythritol) as the carbonific component and melamine as the spumific compound.22 In addition, the intumescent formulations typically contain resinous binders, pigments, and other fillers. These systems are highly efficient in flame-retarding hydroxy-lated polymers. 

A series of compounded flame retardants, based on finally divided insoluble ammonium phosphate together with char-forming nitrogenous resins, has been developed for thermoplastics.23 These compounds are particularly useful as intumescent flame-retardant additives for polyolefins, ethylene-vinyl acetate, and urethane elastomers. The char-forming resin can be, for example, an ethyle-neurea-formaldehyde condensation polymer, a hydroxyethyl isocyanurate, or a piperazine-triazine resin. Commercial leach-resistant flame-retardant treatments for wood have also been developed based on a reaction product of phosphoric acid with urea-formaldehyde and dicyandiamide resins. 

Lewin, M. and Endo, M. 2003. Catalysis of intumescent flame retardancy of polypropylene by metallic compounds. Polymers for Advanced Technologies 14 3-11. 

The so-called intumescents form another class of flame retardants. These are low smoke release flame retardants which combine nitrogen and phosphorus. They are more costly than many halogenated compounds but are used in a.o. wire-and-cable and electronic housing uses where toxic smoke poses an immediate threat [7]. 

Flame retardant polyurethanes are mostly manufactured with compounds of phosphorus, such as ammonium phosphate or polyphosphate. Aluminum hydroxide alone or in combination with melamine is an alternate approach. In intumescent applications, graphite is frequently used. Calcium carbonate is useful as a flame retarding additive, in combination with other flame retarding materials, because of its large endothennic peak found in DTA curves. ... 

The three main types of flame-retardant paints are intumescent paints, antimony oxide/chlorinated resin compounds, and silicate paints. ... 

Flame-retardant properties are exhibited by (tris methyl salicyl) phosphate (12.210a) and cross-linkable derivatives such as (12.210b). Compound (12.210c) is used with polycarbonates, and melamine phosphate (12.210d) is utilised in intumescent paint formulations [42]. Intumescent flame retardants also include [(NH iPOj] and compound (20.210e) [43],... 

Bis(2-chloroethyl)vinylphosphonate, CH CH P(0)(0CH2CH2C1)2 can be used to form emulsion copolymers with vinyl halides, or it may be used on its own and mechanically incorporated into textile fibres. Compound (12.212a) when dispersed in rayon is an effective retardant additive [44], while (12.212b), when copolymerised with a suitable monomer, will act as an intumescent flame retardant. 

Work based in Hungary and France has been examining the claims for a siloxane compoimd to act as a synergist for the protection of polyolefins. Organoboroxo-siloxane (OBSi) is added with APP and pentaerythritol to polypropylene. The material appears to increase the viscosity of the polymer composition and provide some plasticity to the resultant intumescent char. The plasticity allows for better prevention of char cracking and so provides improved flame retardancy. The increased melt viscosity is created by the product of BSi-pentaerythritol, formed during the compound preparation, and the improved char plasticity is the result of products formed at high temperatures from BSi and APP. 

Ethylene-vinyl acetate copolymers, usually known as EVA, are used in many applications, but especially for low voltage cables. These polymers are easily flammable and flame retardants are added to reduce their flammability. The classic solution is to incorporate aluminium hydroxide or magnesium hydroxide that develop endothermic reactions when heated. Nevertheless, large amounts have to be incorporated, often around 60% and this can lead to a loss of mechanical properties in the compound. Intumescent technology that works well with polypropylene has also been tried for EVA polymer systems. 

These are often melamine and derivatives or polyphosphate compounds such as APP. The mode of action of melamine appears to involve endothermic sublimation, acting as a heat sink, vapour-phase dissociation and also self-condensation under suitable conditions. APP achieves its flame retardant effect by intumescence and char formation acting as a barrier to combustion reactions. 

Work in China has shown the synergistie effect of silicotungistic acid (SiW ) on pol q)ropylene flame retarded by an intumescent FR (NP28 phosphorus-nitrogen compound). The tungsten compound increased the thermal stability of the PP formulation at temperatures above 500 °C. The SiWi2 could efficiently promote the formation of compact intumescent charred layers with phosphocarbonaceous structures. 

Intumescent flame retardants (IFR) that contains phosphorus are also used in halogen-free flame-retardant systems. Most reported IFRs are mixtures of the three ingredients, an acid source, a polyol, and a nitrogen-containing compound (Halpem et al. 1984). Since processing of ABS resin requires that the additives withstand temperatures in excess of 200 °C, the commonly used intumescent system, ammonium polyphosphate, pentaerythritol, and melamine, which do not have sufficient thermal stability, cannot be incorporated into ABS resin under normal processing conditions they are usually used in polyolefins. 

Currently, nitrogen compounds are not very widely used as flame retardants, but some growth is now expected. The best known is melamine, although benzoguanamine and acetoguanamine are possible alternatives. Melamine phosphate is used in conjunction with phosphorus compounds in intumescent compositions. Melamine diborate has been used in epoxy polymers, and melamine cyanurate in polyamides. 

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