Mineral flame retardants

Every year in the United States alone there are approximately 5000 deaths as a direct result of fire. Aside from the loss of life, the cost associated with fire damage approaches 0.3% of the gross national product (GNP). These facts illustrate the importance of efficient fire protection and for mineral flame retardants, which play an important role in this issue. The European and North American market for mineral flame retardants are both approximately 340,000 tons per annum, with projected growth rates of 3 and 5%, respectively (Weber, 2000 Hornsby and Watson, 1989, 1990). 

In both Europe and the United States, aluminum trihydrate, or ATH [Al(OH)3)], has by far the largest share of the mineral flame-retardant market however, magnesium hydroxide presently has the highest growth rate. To date, most of the research using magnesium hydroxide has focused on thermoplastics, including ethylene-vinyl acetate copolymer (EVA), polypropylene, acrylonitrile-butadiene-styrene (ABS) copolymer, and modified polyphenylene oxide (Hornsby and Watson, 1986). 

Considering that plastic often takes 40-50% w/w of flame retardants, there is no room for wood filler in WPC, which will not be WPC anymore but rather a mineral-filled plastic. At any rate, replacement of wood fiber of 3-5 0/lb with mineral flame retardant of 20-30 0/lb would significantly increase the cost of the resulting material. All these questions pose a great challenge to WPC manufacturers aiming at fireproof composite deck boards. 

A common disadvantage of chlorine-containing flame retardants is that they have to be added in quantities, which in turn decrease mechanical properties of the polymer materials. The same sitnation in terms of large amount that should be added into the base material holds for mineral flame retardants as well (ATH, Mg(OH)2) however, minerals typically improve both flexural modulus (stiffness) and flexural strength of composites. 

Mineral flame retardants for polyolefins. Technical presentation (www.special-chem4polymers.com). Albemarle Corp. 2008 (downloaded 9 August 2008). 

Severe Resins containing up to 30% glass, mineral, flame-retardant and other filler material Poor (3ood Excellent... 

Physical Dilution. The flame retardant can also act as a thermal sink, increasing the heat capacity of the polymer or reducing the fuel content to a level below the lower limit of flammabiHty. Inert fillers such as glass fibers and microspheres and minerals such as talc act by this mechanism. 

Flame retardants (qv) are incorporated into the formulations in amounts necessary to satisfy existing requirements. Reactive-type diols, such as A/ A/-bis(2-hydroxyethyl)aminomethylphosphonate (Fyrol 6), are preferred, but nonreactive phosphates (Fyrol CEF, Fyrol PCF) are also used. Often, the necessary results are achieved using mineral fillers, such as alumina trihydrate or melamine. Melamine melts away from the flame and forms both a nonflammable gaseous environment and a molten barrier that helps to isolate the combustible polyurethane foam from the flame. Alumina trihydrate releases water of hydration to cool the flame, forming a noncombustible inorganic protective char at the flame front. Flame-resistant upholstery fabric or liners are also used (27). 

Pellets for injection-molding, extmsion, and blow-molding appHcations include mineral-filled, glass-filled, pigmented, and flame-retarded grades. 

A large number of grades is available, one supplier alone offering about 40, including unreinforced, glass- and carbon-fibre reinforced, mineral filler reinforced, impact modified, elastomer modified, flame retardant and various combinations of the foregoing. 

Hydrolysis of polyamide-based formulations with 6 N HC1 followed by TLC allows differentiation between a-aminocaproic acid (ACA) and hexamethylenedi-amine (HMD) (hydrolysis products of PA6 and PA6.6, respectively), even at low levels. The monomer composition (PA6/PA6.6 ratio) can be derived after chromatographic determination of the adipic acid (AA) content. Extraction of the hydrolysate with ether and derivatisa-tion allow the quantitative determination of fatty acids (from lubricants) by means of GC (Figure 3.27). Further HC1/HF treatment of the hydrolysis residue, which is composed of mineral fillers, CB and nonhydrolysable polymers (e.g. impact modifiers) permits determination of total IM and CB contents CB is measured quantitatively by means of TGA [157]. Acid hydrolysis of flame retarded polyamides allows to determine the adipic acid content (indicative of PA6.6) by means of HPLC, HCN content (indicative of melamine cyanurate) and fatty acid (indicative of a stearate) by means of GC [640]. Determination of ethylene oxide-based antistatic agents... 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

These can be inorganic materials such as calcium silicate, mineral wool, diatomaceous earth or perlite and mineral wool. If provided as an assembly they are fitted with steel panels or jackets. These are woven noncombustible or flame retardant materials the provide insulation properties to fire barrier for the blockage of heat transfer. 

Uses Component of fire extinguisher fluids solvent for waxes, fats, and resins degreaser flame retardant heavy liquid for mineral and salt separations chemical intermediate laboratory use. 

Decabromodiphenyl ether (BDE-209) is a major industrial product from the polybrominated diphenyl ethers used as flame retardants derivatives of this product have been detected in the environment. After exposure to the land surface, these contaminants adsorb on soil materials and may reach the atmosphere as particulate matter these particulates are subsequently subject to photolytic reactions. In this context, Ahn et al. (2006) studied photolysis of BDE-209 adsorbed on clay minerals, metal oxides, and sediments, under sunhght and UV dark irradiation. Dark and light control treatments during UV and sunlight irradiation showed no disappearance of BDE-209 during the experiments. Data on half-lives and rate constants of BDE-209 adsorbed on subsurface minerals and sediments, as determined by Ahn et al. (2006) and extracted from the literature, are shown in Table 16.6. 

The technical suitability of insulation materials is described by a series of technical parameters relating to the material (heat conductivity and heat storage capacities, damp protection, fire protection class, noise-insulating effect, properties related to building biology, e g. content of hazardous substances such as flame retardants and insecticides). Mineral wools have certain advantages over other insu-... 

Antimony trioxide occurs in nature as minerals, valentinite [1317-98-2] and senarmontinite [12412-52-1]. It is used as a flame retardant in fabrics as an opacifier in ceramics, glass and vitreous enamels as a catalyst as a white pigment in paints as a mortar in the manufacture of tartar emetic and in the production of metallic antimony. 

Lead dichloride occurs in nature as the mineral cotunnite. The compound is used in making many basic chlorides, such as Pattison s lead white. Turner s Patent Yellow, and Verona Yellow, used as pigments. Also, it is used as a flux for galvanizing steel as a flame retardant in nylon wire coatings as a cathode for seawater batteries to remove H2S and ozone from effluent gases as a sterilization indicator as a polymerization catalyst for alpha-olefins and as a co-catalyst in manufacturing acrylonitrile. 

Zinc oxide occurs in nature as mineral zincite. It is the most important zinc compound and has numerous industrial applications. Zinc oxide is the pigment in white paints. It is used to make enamels, white printing inks, white glue, opaque glasses, rubber products and floor tiles. It is used in cosmetics, soaps, pharmaceuticals, dental cements, storage batteries, electrical equipment, and piezoelectric devices. Other applications are as a flame retardant, as a UV absorber in plastics, and a reagent in analytical chemistry. A major application of zinc oxide is in the preparation of most zinc salts. In medicine, the compound is used as an antiseptic, an astringent and a topical protectant. 

One of the emerging technologies that is showing great promise is the use of hydrated mineral fillers such as aluminium and magnesium hydroxides, as such materials can provide high levels of flame retardancy without the formation of smoke or corrosive and potentially toxic fumes. The use of fillers as flame retardants has recently been reviewed by Rothon [23]. Essentially the key features are an endothermic decomposition to reduce the temperature, the release of an inert gas to dilute the combustion gases and the formation of an oxide layer to insulate the polymer and to trap and oxidise soot precursors. 

It is self evident that mineral fillers need to be stable at the temperatures (up to 350 °C) experienced in processing thermoplastics. Most fillers are stable to much higher temperatures and so this is not usually an issue. However, it is a very important topic for flame retardant fillers which function by decomposing endothermically with the release of inert gasses. To be effective, this decomposition must occur near to the temperature at which the polymer begins to decompose and release flammable volatiles. This is usually not too much above the processing temperature in the case of thermoplastics and hence the exact temperature at which decomposition commences is of great importance. The size and position of the endotherm and the rate at which the inert gas is released are also of importance to the flame retardant effect itself [23]. 

Magnesium hydroxide occurs in nature as the mineral brucite. It has a Moh hardness of about 3 and a specific gravity of 2.4. It starts to decompose endothermically with the release of water at about 300 °C and the principal interest in it is as a flame retardant filler for thermoplastics such as polyolefins and polyamides, where the processing temperature is too high for aluminium hydroxide to be utilised effectively. For thermoplastic appHcations low aspect ratio particles are favoured with a particle size of about 1 micron and a specific surface area in the range 4-10 m2 g ... 

The development of the different methods for the production of flame retardant grade magnesium hydroxide has recently been reviewed [100]. Although not a common mineral, there are some workable deposits of brucite, especially in the US and China and product obtained by milling high purity brucite deposits is being marketed, but has so far made little impact. This is probably because the high levels needed for flame retardancy can only be tolerated if the particle size and shape are carefully controlled and this requires the use of synthetic methods of production. 

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