Flame Retardants and Smoke Suppressants

Most commercial plastics are readily combustible, and some evolve dark smoke on binning. This smoke is indirectly responsible for most fire fatalities. The cost of fire damage to buildings and contents has been estimated at up to 30 billion euros/year in Europe. 

There are two ways to reduce polymer flammability. A few (mostly thermosetting) polymers can have their synthesis modified by replacing part of the starting materials with chemically reactive halogenated analogues. 

The effectiveness of flame retardant additives can be ascertained by a wide variety of methods. Some are only appropriate for laboratory comparisons between materials, whereas standard fire tests are designed to give regulatory approval. 

None of the tests can be guaranteed to give an accurate representation of what happens in a fire, because the flammability of plastics formulations is a very complex matter, and factors like sample size and geometry, proximity of other combustible materials, prevailing temperatures, wind speed and direction, and the scope for rapid heat dissipation vary with the circumstances. 

Test procedures used in recent years include  

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Alumina trihydtate is also used as a secondary flame retardant and smoke suppressant for flexible poly(vinyl chloride) and polyolefin formulations in which antimony and a halogen ate used. The addition of minor amounts of either zinc borate or phosphoms results in the formation of glasses which insulate the unbumed polymer from the flame (21). 

In halogen-free polymers, the zinc borate in combination with ATH at high loadings can also function as a flame retardant and smoke suppressant by releasing water and forming a porous ceramic residue, which acts as a thermal insulator. 

At the present time, inorganic tin compounds find a relatively small use in natural polymers, particularly as flame-resist treatments for woollen rugs and sheepskins (8,9). Although certain other metal derivatives have received more attention, there has been much interest recently in the potential use of tin chemicals as flame retardants and smoke suppressants for synthetic polymers (10). 

Hence, it is apparent that certain inorganic tin compounds are very effective flame retardants and smoke suppressants for halogenated polymer formulations. Since these additives are generally non-toxic, their potential use as partial or total replacements for existing commercial flame retardants, such as antimony trioxide, is thought to merit serious consideration. 

Goethite is used in flame retardants and smoke suppressants. Both laboratory and large scale pilot tests showed that goethite is the most active smoke suppressant when polymers and plastics are burned (Carty and White, 1999 Carty et al., 1999). It reduces the amount of smoke produced during pyrolysis in air of chlorinated PVC plasticized with dioctylphthalate, by changing the decomposition pathway followed by phthalate, so that benzene, which is produced in the absence of the smoke suppressant, is not formed (Carty et al., 1999). 

Green J (1989) Flame retardants and smoke suppressants. In Katz HS, MUewski JV (eds) Handbook of fiUers for plastics. Van Nostrand, New York, chapter 4, p93 Hornsby PR, Watson CL (1986) Plast Rubber Process Appl 6 169 Rothon RN (1995) Effects of particulate fiUers on flame retardant properties of polymers. In Rothon RN (ed) Particulate-fiUed polymer composites. Longman, Harlow, Chap 6,p207... 

Molybdenum compounds can act as flame retardants and smoke suppressants in textiles and in plastics233,275. Heteropoly compounds have been found to act as... 

D. Price, Y. Liu, G.J. Milnes, T.R. Hull, B.K. Kandola, and A.R. Horrocks, An investigation into the mechanism of flame retardancy and smoke suppression by melamine in flexible polyurethane foam. Fire Mater., 26, 201-206 (2002). 

By reacting aluminum hydroxide with oxalic acid, basic aluminum oxalate can be produced, which is thermally stable to 330°C, losing 51% of its mass on decomposition at temperatures above 450°C. It is reported to have a flame-retarding and smoke-suppressing action similar to ATH, but because of its increased thermal stability, it can be used in polyamides and thermoplastic polyesters. However, unlike magnesium hydroxide, in these polymers it does not cause hydrolytic degradation.2... 

Wan Hanafi, W.Z.A., A study of magnesium hydroxide as a flame retardant and smoke suppressant for unsaturated polyesters, MPhil thesis, Brunei University, London, U.K., July, 1988. 

Hornsby, P.R. and Watson, C.L., A study of the mechanism of flame retardancy and smoke suppression in polymers filled with magnesium hydroxide, Polym. Deg. Stab., 30, 73-87,1990. 

Cusack, P.A. and Hornsby, P.R., Zinc hydroxystannate/zinc stannate-coated fillers Novel flame retardants and smoke suppressants for polymeric materials, J. Vinyl Additive Technol., 5, 21-30, 1999. 

This zinc borate is a more effective flame retardant and smoke suppressant than barium metaborate (Busan 11M1).43 For example, in flexible PVC, a combination of antimony trioxide and the zinc borate results in much better fire test performances than the antimony trioxide and barium metaborate combination (Table 9.4). In contrast to flexible PVC, this zinc borate alone improves both fire retardancy and smoke suppression in rigid PVC.48... 

Shen, K.K. 2006. Overview of flame retardancy and smoke suppressant in flexible PVC. Society of Plastics Engineering Vinyltech Conference, Atlanta, GA, October 18. 

Shen, K.K. and Sprague, R.W. 1982. Zinc borate as a flame retardant and smoke suppressant in epoxy systems. J. Fire Retardant Chem., 9, 161. 

Shi, L. Li, D., Wang, J., Li, S., Evans, D.G., and Duan, X. 2005. Synthesis, flame retardant and smoke-suppressant properties of a borate-intercalated layered double hydroxide. Clays Clay Miner., 53(3), 294-300. 

Bonsignore, P.V. Levendusky, T.L. Alumina trihydrate as a flame retardant and smoke suppressive filler in rigid high density polyurethane foams. J. Fire Flammability 1977, 8, 95-114. 

Qu, H. Wu, W. Wie, H. Xu, J. Metal hydroxystannates as flame retardants and smoke suppressants for semirigid poly(vinyl chloride). J. Vinyl Addit. Technol. 2008, 14, 84-90. 

Levchik, S.V. and Weil, E.D., Review Overview of the recent literature on flame retardancy and smoke suppression in PVC, Polym. Adv. Technol., 2005, 16, 707-716. 

Use for magnesium hydroxide is in pulp and paper, Epsom salts, waste water treatment, flame retardants, and smoke suppressants. 

PVC-U formulations have low flammability due to the chlorine content. The addition of plasticiser in PVC-P formulations necessitates the use of flame retardant and smoke suppressant additives. These additives are known as functional fillers and a correct balance is necessary to achieve all the end-use specification requirements. They are predominately used in cable, conveyer belting and roofing membrane formulations to give resistance to fire initiation and propagation. It is also important to reduce dripping in a fire situation and that as little smoke as possible is generated. Antimony trioxide has been used extensively, usually in combination with phosphate ester plasticisers, giving excellent fire performance and mechanical properties. 

The results are reported of a study of the effect of various polymeric additives and metal oxides on the thermal degradation, flame retardancy and smoke suppression of rigid PVC carried out using a cone calorimeter at an incident heat flux of 25 kW sq.m. Polymeric additives... 

Details are given of the addition of flame retardant and smoke suppressant additives to PVC to meet specifications such as oxygen index, heat release, smoke evolution or extent of burning in cable tests. Data are presented for synergistic combinations of additives in PVC formulations. 31 refs. 

Journal of Applied Polymer Science 77, No. 14, 29th Sept.2000, p.3119-27 FLAME-RETARDANT AND SMOKE-SUPPRESSANT PROPERTIES OF ZINC BORATE AND ALUMINIUM TRIHYDRATE-FILLED RIGID PVC... 

Journal of Fire Sciences 14, No.6, Nov/Dec.1996, p.426-42 MECHANSIMS FOR FLAME RETARDANCY AND SMOKE SUPPRESSION - REVIEW... 

Flame retardant and smoke suppressant fillers in a variety of organic coatings used for textile products. 

By far the most important tin-based fire retardants are the zinc stannates - zinc hydroxystannate (ZHS) and its anhydrous analog, zinc stannate (ZS). Originally developed at ITRI during the mid-1980s, these additives are now being marketed worldwide as non-toxic flame retardants and smoke suppressants for use in a wide range of polymeric materials. ... 

Apart from ZHS and ZS, little work has generally been undertaken on tin-based Are retardants in nonhalogen polymer systems. However, certain tin(II) compounds have shown excellent flame-retardant and smoke-suppressant properties when incorporated at levels of 20-30% into aromatic polyesters, specifically polybutylene terephthalate (PBT). Hence, tin(ll) oxide, tin(II) oxalate, and tin(II) phosphate have been shown to markedly increase flame retardancy in PBT, whereas, interestingly, tin(IV) oxide is almost totally ineffective in the same polymeric substrate. 

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