Fire-safe polymers

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Fire-safe polymers are

insulation for electronics,[3] and in military materials such as canvas tenting.[4]

Some fire-safe

polymers was begun in 1995. The Center for UMass/Industry Research on Polymers (CUMIRP) was established in 1980 in Amherst, MA as a concentrated cluster of scientists from both academia and industry for the purpose of polymer science and engineering research.[1]

History

Early history

Controlling the

acids. These early attempts found application in reducing the flammability of wood for military materials, theater curtains, and other textiles, for example. Important milestones during this early work include the first patent for a mixture for controlling flammability issued to Obadiah Wyld in 1735,[4] and the first scientific exploration of controlling flammability, which was undertaken by Joseph Louis Gay-Lussac in 1821.[4]

Developments since WWII

Research on fire-retardant

polymers are usually more efficient at deterring combustion.[4]

Polymer combustion

General mechanistic scheme

Traditional polymers decompose under heat and produce combustible products; thus, they are able to originate and easily propagate fire (as shown in Figure 1).

Figure 1: A general scheme of polymer combustion.

The

flammability limits, and at a temperature above the ignition temperature, then combustion proceeds. As long as the heat supplied to the polymer remains sufficient to sustain its thermal decomposition at a rate exceeding that required to feed the flame, combustion will continue.[7]

Purpose and methods of fire-retardant systems

The purpose is to control heat below the critical level. To achieve this, one can create an

endothermic environment, produce non-combustible products, or add chemicals that would remove fire-propagating radicals (H and OH), to name a few. These specific chemicals can be added into the polymer molecules permanently (see Intrinsically Fire-Resistant Polymers) or as additives and fillers (see Flame-Retardant Additives and Fillers).[7]

Role of oxygen

polymers exhibit a structural-dependent relationship with oxygen. Some structures are intrinsically more sensitive to decomposition upon reaction with oxygen. The amount of access that oxygen has to the surface of the polymer also plays a role in polymer combustion. Oxygen is better able to interact with the polymer before a flame has actually been ignited.[7]

Role of heating rate

In most cases, results from a typical heating rate (e.g. 10°C/min for mechanical

thermal degradation studies) do not differ significantly from those obtained at higher heating rates. The extent of reaction can, however, be influenced by the heating rate. For example, some reactions may not occur with a low heating rate due to evaporation of the products.[7]

Role of pressure

Volatile products are removed more efficiently under low pressure, which means the stability of the polymer might have been compromised. Decreased pressure also slows down decomposition of high boiling products.[7]

Intrinsically fire-resistant polymers

The

hydrogen bonding between the polymer chains can all enhance fire-resistance.[8]

Linear, single-stranded polymers with cyclic aromatic components

Most intrinsically fire-resistant

polymers.[10]

Ladder polymers

insoluble
.

Inorganic and semiorganic polymers

Inorganic and semiorganic

inorganic polymer that can be thermally stable up to temperatures of 1300-1400 °C.[12]

Flame-retardant additives and fillers

Additives are divided into two basic types depending on the interaction of the additive and

covalently bound to the polymer; the flame retardant and the polymer
are just physically mixed together. Only a few
aluminum, phosphorus, nitrogen, antimony, chlorine, bromine, and in specific applications magnesium, zinc and carbon. One prominent advantage of the flame retardants (FRs) derived from these elements is that they are relatively easy to manufacture. They are used in important quantities: in 2013, the world consumption of FRs amounted to around 1.8/2.1 Mio t for 2013 with sales of 4.9/5.2 billion USD. Market studies estimate FRs demand to rise between 5/7 % pa to 2.4/2.6 Mio t until 2016/2018 with estimated sales of 6.1/7.1 billion USD.[13]

The most important flame retardants systems used act either in the gas phase where they remove the high energy radicals H and OH from the flame or in the solid phase, where they shield the polymer by forming a charred layer and thus protect the polymer from being attacked by oxygen and heat.[14] Flame retardants based on bromine or chlorine, as well as a number of phosphorus compounds act chemically in the gas phase and are very efficient. Others only act in the condensed phase such as metal hydroxides (aluminum trihydrate, or ATH, magnesium hydroxide, or MDH, and boehmite), metal oxides and salts (zinc borate and zinc oxide, zinc hydroxystannate), as well as expandable graphite and some nanocomposites (see below). Phosphorus and nitrogen compounds are also effective in the condensed phase, and as they also may act in the gas phase, they are quite efficient flame retardants. Overviews of the main flame retardants families, their mode of action and applications are given in.[15][16] Further handbooks on these topics are [17][18] A good example for a very efficient phosphorus-based flame retardant system acting in the gas and condensed phases is aluminium diethyl phosphinate in conjunction with synergists such as melamine polyphosphate (MPP) and others. These phosphinates are mainly used to flame retard polyamides (PA) and polybutylene terephthalate (PBT) for flame retardant applications in electrical engineering/electronics (E&E).[19]

Natural fiber-containing composites

Besides providing satisfactory mechanical properties and renewability, natural fibers are easier to obtain and much cheaper than man-made materials. Moreover, they are more environmentally friendly.[20] Recent research focuses on application of different types of fire retardants during the manufacturing process as well as applications of fire retardants (especially intumescent coatings) at the finishing stage.[20]

Nanocomposites

flammability.[21]

Problems with additives and fillers

Although effective at reducing

polymers. Besides, addition of many fire-retardants produces soot and carbon monoxide during combustion. Halogen-containing materials cause even more concerns on environmental pollution.[1][22]

See also

References

  1. ^ a b c d e f Zhang, H. Fire-Safe Polymers and Polymer Composites, Federal Aviation Administration technical report; U.S. Department of Transportation: Washington, D.C., 2004.
  2. ^ Sarkos, C. P. The Effect of Cabin Materials on Aircraft Postcrash Fire Survivability. Technical Papers of the Annual Technical Conference 1996, 54 (3), 3068-3071.
  3. ^
    doi:10.1002/pola.1993.080311109
  4. ^
    ISSN 0097-6156
  5. doi:10.1021/ie50536a034
  6. ^ Connolly, W. J.; Thornton, A. M. Aluminum Hydrate Filler in Polyester Systems. Mod. Plastics 1965, 43 (2), 154-202.
  7. ^
    doi:10.1016/0141-3910(91)90014-I
  8. doi:10.1002/app.1969.070130822
  9. doi:10.1002/(SICI)1097-4628(20000411)76:2<240::AID-APP13>3.0.CO;2-A
  10. doi:10.1016/S0032-3861(96)00778-1
  11. ISSN 0003-3146
  12. doi:10.1016/S1466-6049(00)00041-6
  13. ^ Troitzsch, J.H. Flame retardants. Demands and innovations. 5th International SKZ Conference on Flame Retardant Plastics, Shanghai, China, 21 March 2014
  14. ^ Lewin, M., Weil, E. Mechanisms and modes of action in flame retardancy of polymers, p. 31 f., in Fire retardant materials, Horrocks, R., Price, D. Ed., Woodhead Publishing, 2004
  15. ^ Bourbigot, S., Le Bras, M. Flame retardants, p. 133 f. and Eckel, T. Flame retarded plastics, p. 158 f. in Plastics flammability handbook, 3rd Ed., Troitzsch, J. Ed., Hanser Publishers, Munich, 2004
  16. ^ Weil, E., Levchik S. Flame retardants for plastics and textiles. Practical applications. Hanser Publishers, Munich, 2009
  17. ^ Wilkie, C., Morgan, A. Fire retardancy of organic materials, 2nd Ed., CRC Press, 2010
  18. ^ Morgan, A., Wilkie, C. Non halogenated flame retardant handbook, Scrivener Publishing, Wiley, 2014.
  19. ^ Huang, K.J., Hörold, S., Dietz, M., Schmitt, E. Phosphinates as flame retardants for plastics in electronics. 1st International SKZ Conference on Flame Retardant Plastics, Shanghai, China, 21 September 2009
  20. ^
    doi:10.1002/pat.1135
  21. ^
    doi:10.1002/masy.200650123
  22. doi:10.1002/(SICI)1099-1018(200001/02)24:1<45::AID-FAM719>3.0.CO;2-S

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