Polymeric system, fire retarded

Chlorinated paraffins are versatile materials and are used in widely differing appHcations. As cost-effective plasticizers, they are employed in plastics particularly PVC, mbbers, surface coatings, adhesives, and sealants. Where required they impart the additional features of fire retardance, and chemical and water resistance. In conjunction with antimony trioxide, they constitute one of the most cost-effective fire-retardant systems for polymeric materials, textiles, surface coatings, and paper products. Chlorinated paraffins are also employed as components in fat Hquors used in the leather industry, as extreme pressure additives in metal-working lubricants, and as solvents in carbonless copying paper. 

Borates, through their ability to act as glass network formers, can act as excellent char formers and drip suppressants in fire retardant applications. In many cases this involves processing into polymeric materials, leading to specific requirements for thermal stability and particle size. Most common borate materials, however, exhibit relatively low dehydration temperatures and may be unsuitable for use in many polymer systems. Zinc borates are often used because they have unusually high dehydration onset temperatures and can be produced as small particle size powders. 

An extensive study was conducted on the effect of chemical and structural aspects of zeolites on the fire performance of the intumescent system, ammonium polyphosphate-pentaerythritol (APP-PER), where a marked improvement of the fire-retardant properties within different polymeric matrices has been observed.56 58 The synergistic mechanism of zeolite 4A with the intumescent materials was investigated using solid-state NMR. Chemical analysis combined with cross-polarization dipolar-decoupled magic-angle spinning NMR revealed that the materials resulting from the thermal treatment of the APP-PER and APP-PER/4A systems were formed by carbonaceous and phosphocarbonaceous species, and that the zeolite enhances the stability of the phosphocarbonaceous species. 

Duquesne, S., Le Bras, M., Jama, C., Weil, E.D., and Gengembre, L. 2002. X-ray photoelectron spectroscopy investigation of fire retarded polymeric materials Application to the study of an intumescent system. Polymer Degradation and Stability 77(2) 203-211. 

Design of Interlayers for Fire-Retarded Polymeric Systems... 

In addition to the basic plastics in liquid and bead forms with foaming agents, fillers, additives that include cell controllers and fire-retardants, catalysts, surfactants, styrene monomer, systems that vary viscosity from liquid to paste form, and other additives are used. The gas can be put directly in to the plastic before the plastic solidifies. Reactant chemicals can be put in the plastic formulation that during polymerization will release a gas and produce the foam. 

The externally applied physical and chemical measures of affecting a polymeric system are used in practice to extinguish a fire already under way. However, the problem of flame retardance of polymers actually impUes using any measures to preclude or retard the development of fire. In other words, the physical and chemical factors must be effective within the system itself. 

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... 

Most fire-retardant formulations are not resistant to leaching by water. Therefore, there have been increased efforts to develop leach-resistant chemicals that can be impregnated into wood products for use in exterior or high humidity applications. Some of the proposed leach-resistant systems include chemical combinations that form insoluble complexes, amino-resin systems, and monomers that polymerize in the wood. 

Much literature discusses the flame retardation of various polymeric materials (10-15). The techniques of reducing the flammability of polymers, in principle, are based on one or more of the three fundamental approaches described earlier. This section deals with the concept of synergism and its application in reducing flammability, selection of fire-retardant additives, and flame retarding some specific polymer systems. 

In any given fire retardant one or more above methods may be used. The effect of a fire-retardant strongly depends on the basic chemical structure of the polymeric material. Owing to complexity of the processes and the experimental limitations, it is difficult to predict which mechanism is most important or operative for any system. A list of commercially available fire-retardants is given in Appendix-1. These materials are classified as organic, inorganic and reactive types. A fact to be kept in mind is that for blends or alloys, the fire retardancy behavior is usually between those of the base resins for example, consider Arylon and Kydene (acrylic/PVC) [Landrock, 1983]. 

It is also possible to build into the chemical systems other properties that are desired in the treated wood. Fire retardancy, chemical resistance, or resistance to ultraviolet radiation can be built into the bonding or polymerizing systems. Thus, serious problems can be solved while stability, strength, and integrity are improved. 

First of all, halogen-based fire retardant additives (especially bromin-ated compounds associated with the antimony trioxide) are widely used. These systems release obscuring, corrosive and toxic smoke when they perform their fire retardant action. More, some of them release super toxic compoimds ( dioxins and polybrominated dibenzofurans) when exposed to heat during manufacturing or in fire. A continuous trend is the development of polymeric materials with reduced fire hazard, in order to meet the requirement of the international regulations (5th OECD Draft Status report (04/1993) and UN Environmental Program 1st Draft Report (01/1993)). 

Weil, E.D. Synergists, adjuvants and antagonists in flame retardant systems, in A.F. Grand and C.A. Wilkie, Eds., Fire Retardancy of Polymeric Materials. Marcel Dekker, New York, 1999, pp. 115-145. 

In this section we have demonshated that intumescent systems provide efficient fire retardant properties to polymeric materials, both in bulk and as a coating. The mechanisms of action have been discussed and we have seen that the chemistry of such systems offers some flexibility in the synthesis of the char (e.g., potential reactivity of phosphates and oxidized functions). We can then expect to enhance the performance of the intumescent char by the addition of other reactive compounds in the formulation, which is the purpose of the next section. 

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