Design of flame retardants

We note at the outset that our objective is not immediately to design flame retardants, rather it is to build up enough information that will permit the design of flame retardants. None of the materials that are described in this paper would be suitable additives, however the detailed reaction information that becomes available through this work will permit flame retardants to be designed. 

A detailed understanding of the course of a reaction between a polymer and an additive will permit one to use that information to design new flame retardants. The reaction between poly(methyl methacrylate), PMMA, and red phosphorus is described and that information used to determine that CIRh(PPh3)3 should be used as a flame retardant. The results of this investigation are then used to choose the next additive. A recurring theme is the efficacy of cross-linking as a means to impart an increased thermal stability. 

A. Szabo, B. Marosfoi, P. Anna, and Gy. Marosi, Complex micro-analysis assisted design of fire retardant nanocomposites—Contribution to the nano-mechanism, to be published in Flame Retardancy of Polymers New Strategies and Mechanisms, T.R. Huh and B.K. Kandola (eds.), The Royal Society of Chemistry, Cambridge, U.K., 2009, pp. 74—91. 

Drysdale DD. Fire safety design requirements of flame-retarded materials. In Fire Retardant Materials. Horrocks AR, Price D, Eds. Woodhead Publishing Cambridge, U.K., 2001 chap. 13, pp. 378-397. 

Velsicol Chemical LLC, formerly Velsicol Chemical Corporation, designs, manufactures, markets and distributes high performance specialty chemicals and industrial intermediates, primarily based on benzoic acid and the organic compound cyclopentadiene. Its products include chlorendic anhydride and hexachlorocyclopentadiene (HEX). Chlorendic anhydride is corrosion resistant, fire resistant and has high UV stability, and is used in the synthesis of flame retardant polymers such as polyurethanes, unsaturated polyester and epoxy resins. HEX, a reactive intermediate used in the manufacture of agricultural pesticides in the production of flame retardants for the wire and cable industry and in the preparation of chlorendic anhydride. The company s products are produced primarily at a plant in Memphis, Tennessee Velsicol also maintains the Memphis Environmental Center (MEC), which focuses on managing legacy environmental liabilities. The firm is owned by Arsenal Capital Partners, a private equity firm. 

Ammonium zirconyl carbonate, (NH4)3[ZrOH(COj)3] 2H2O is a constituent of flame-retarding systems used for cotton fabrics designed for outdoor use, such as tenting. It is also employed as a water repellent in floor polishes and paper coatings, for the production of zirconium oxide films and as an adhesive in lithography. The anion has a polymeric, hydroxide-bridged structure (5). 

Condensed phase. In condensed-phase modification, the flame retardant alters the decomposition chemistry so that the transformation of the polymer to a char residue is favored. This result could be achieved with additives that catalyze char rather than flammable product formation or by designing polymer structures that favor char formation. Carbonization, which occurs at the cost of flammable product formation, also shields the residual substrate by interfering with the access of heat and oxygen. Phosphorus-based additives are typical examples of flame retardants that could act by a condensed phase mechanism. 

A special grade, FR-372 has been designed for PP fibre and textiles. The usual method of application is via a masterbatch containing 30-40% of flame retardant. This concentrate is then diluted in the PP to reach around 3-5% of FR-372 in the final composition. 

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. 

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