Retarders, vapour phase

Antimony trioxide (SbaOj). It is produced from stibnite (antimony sulphide). Some typical properties are density 5.2-5.67 g/cm- pH of water suspension 2-6.5 particle size 0.2-3 p,m specific surface area 2-13 m-/g. Antimony trioxide has been the oxide universally employed as flame retardant, but recently antimony pentoxide (SbaOs) has also been used. Antimony oxides require the presence of a halogen compound to exert their fire-retardant effect. The flame-retarding action is produced in the vapour phase above the burning surface. The halogen and the antimony oxide in a vapour phase (above 315 C) react to form halides and oxyhalides which act as extinguishing moieties. Combination with zinc borate, zinc stannate and ammonium octamolybdate enhances the flame-retarding properties of antimony trioxide. 

New photoreactive polymers with dimethylmaleimide side groups have been prepared, "" and co-polymers of methyl methacrylate with oligourethanes have tensile properties superior to those of the separate homopolymer systems."" New monomers have been prepared for fire-retardant u.v.-curable polymers " and trimethylolpropane has been photopolymerized in the vapour phase. Diphenylsulphoniumbis(methoxycarbonyl)methylide photoinitiates the polymerization of styrene and methyl methacrylate through the formation of... 

Polymerization Studies. Anionic Polymerization of Caprolactam (the use of (CFs C0)20 (ca. 2 mole %) enabled a lower reaction temperature to be employed and higher yiel and polyamide molecular weights to be obtained]. Soil-retardant Finishing of Cotton Ooth by Vapour-phase Graft Polymerization of Fluoroalkyl Acrylates. Radical Polymerization of a-Fluoroacrylic Acid and -Vinylpyrrolidone in an Aqueous Solution. Perfluoropolyether Esters of Quinones [the preparation of the title compounds by reaction of 1.5-dihydroxyanthraquinone with per-fluoropolyetheracyl fluorides, e.g. CFj-CFi-CF -O-CF(Ci )-CaPj-O-CF(CF,)-C50F, is... 

The presence of a liquid phase is essential to the reaction of low volatility reactants in the other cases, it allows to save the high temperature energy related to the vaporization of the reactant and to the operation in the vapour phase. It makes possible the optimization of the selectivity by an appropriate choice of the solvent. It allows also some kind of prevention or retardation of catalyst poisoning and it provides a good help for temperature control. 

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. 

ACTION OF FLAME RETARDANTS Inhibition of vapour phase combustion... 

Steps (iv) and (v) are thought to be the main chain branching steps in combustion. Several flame retardants act by inhibiting this vapour phase combustion. They produce decomposition products (at the same temperature as the polymer substrate decomposes) which interfere with the chain branching steps in combustion. Less reactive radicals are formed, which inhibit the combustion process. 

Zinc borate in halogenated systems, such as flexible PVC, is known to increase markedly the amount of char formed during polymer combustion whereas the addition of antimony, a vapour phase flame retardant, has little effect on char formation. The hydrogen chloride released from PVC thermal degradation can react with the zinc borate [6] to form zinc hydroxychloride and zinc chloride as well as boric oxide and boron trichloride (equation 5). 

There are three essential conditions to be met if a polymer, once ignited, is to continue burning. There must be a supply of heat to the bulk polymer, a generation of fuel (typically volatile decomposition products) and there must be a flame. Halogen-based systems act by a well-documented flame poisoning mechanism in the vapour phase. The alternative halogen-free systems, which encompass a wide variety of additives, tend to act by mechanisms which disrupt heat flow and the supply of fuel to the flame. Here the mechanisms are not always understood in great detail but two broad types of flame retardant action can be defined. 

Besides the use of melamine as a component of intumescent systems it has also been advocated as a flame retardant in its own right. It has the advantages of being inexpensive, readily dispersible in most thermoplastics and is commercially available in grades of varying particle size. The flame retardant effect is largely due to a combination of heat sink effects and vapour phase dilution effects so in these respects it has some similarities with the hydrated filler flame retardants. 

Although much work has been carried out on the mode of action of flame retardants generally, the mechanisms associated with tin additives are only partially understood. It is clear that tin-based fire retardants can exert their action in both the condensed and vapour phases, and that the precise action in any particular system depends on a number of factors, including incorporation level, the amount and chemical nature of other additives present and, indeed, the nature of the polymer itself. 

The tin additives exert their fire-retardant action in both the condensed and vapour phases, by promoting the formation of a thermally stable carbonaceous char and (in halogen-containing polymer formulations) by generating volatile metal halide species which assist in free radical scavenging reactions in the flame. 

The oxidation that occurs in the vapour phase is a free radical process and additives that can trap radicals such as H , O, HO2 and OH may be useful as flame retardants. Halogen-containing compounds are an example of particularly good radical scavengers and thus halogenated organic compounds find extensive use in flame retarded compound formulations. 

The reaction mechanisms are quite complicated in these syntheses, the kinetics depending on inter-diffusion rates in neighbouring particles, the formation of transient liquid phases, and in some cases, the vapour transport of a reactant. The presence of the latter can be detected by dre retarding effect of increased pressure in an inert surrounding atmosphere. 

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