Zinc-based flame retardant

DeFenzo,A. Formicola,C. Antonucci,V. Zarrelli,M. and Giordano,M.,Effects of zinc-based flame retardants on the degradation behaviour of an aerospace epoxy matrix, Polym. Degrad. Stab., 94(9), 1354-1363 (2009) DOI 10.1016/j. polymdegradstab.2009.05.020. 

Boron compounds such as borax and boric acid are well-known fire retardants in cellulosic products and coatings.12 However, the use of boron compounds such as zinc borate, ammonium pent-aborate (APB), melamine borate, boric oxide, boron phosphate, and other metal borates in polymers has become prominent only since early 1980s.3 6 This chapter will review the chemical and physical properties, the end-use applications, as well as the mode of actions of major boron compounds as fire retardants in different applications. Since boron-based flame retardants are extensively used and quoted in literature, only those formulations of commercial importance and representative literature examples will be discussed and/or cited in this chapter. 

Polyolefins When used in conjunction with a halogen-based flame retardant, this zinc borate can partially replace antimony oxide (30%-40%) and still maintain the same fire test performance. In addition, it can improve aged elongation properties, increase char formation, and decrease smoke generation. The B203 moiety in zinc borate can also provide afterglow suppression (Table 9.6). 

Organophosphoms compounds, primarily phosphonic acids, are used as sequestrants, scale inhibitors, deflocculants, or ion-control agents in oil wells, cooling-tower waters, and boiler-feed waters. Organophosphates are also used as plasticizers and flame retardants in plastics and elastomers, which accounted for 22% of PCl consumed. Phosphites, in conjunction with Hquid mixed metals, such as calcium—zinc and barium—cadmium heat stabilizers, function as antioxidants and stabilizer adjutants. In 1992, such phosphoms-based chemicals amounted to slightly more than 6% of all such plastic additives and represented 8500 t of phosphoms. Because PVC production is expected to increase, the use of phosphoms additive should increase 3% aimually through 1999. 

Other flame retardants and/or smoke suppressants can also be used such as magnesium hydroxide, magnesium carbonate, magnesium-zinc complexes and some tin-zinc compositions. Zinc oxide is a common ingredient in many rubber base formulations used as part of the curing system. At the same time, the action of zinc oxide is similar to that of antimony trioxide, but less effective. 

Paints are complex formulations of polymeric binders with additives including anti-corrosion pigments, colors, plasticizers, ultraviolet absorbers, flame-retardant chemicals, etc. Almost all binders are organic materials such as resins based on epoxy, polyurethanes, alkyds, esters, chlorinated rubber and acrylics. The common inorganic binder is the silicate used in inorganic zinc silicate primer for steel. Specific formulations are available for application to aluminum and for galvanized steel substrates. 

Zinc in contact with wood Zinc is not generally affected by contact with seasoned wood, but oak and, more particularly, western red cedar can prove corrosive, and waters from these timbers should not drain onto zinc surfaces. Exudations from knots in unseasoned soft woods can also affect zinc while the timber is drying out. Care should be exercised when using zinc or galvanised steel in contact with preservative or fire-retardant-treated timber. Solvent-based preservatives are normally not corrosive to zinc but water-based preservatives, such as salt formulated copper-chrome-arsenic (CCA), can accelerate the rate of corrosion of zinc under moist conditions. Such preservatives are formulated from copper sulphate and sodium dichromate and when the copper chromium and arsenic are absorbed into the timber sodium sulphate remains free and under moist conditions provides an electrolyte for corrosion of the zinc. Flame retardants are frequently based on halogens which are hygroscopic and can be aggressive to zinc (see also Section 18.10). 

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. ... 

Thermal analysis experiments have clearly shown that tin-based fire retardants markedly alter both the initial pyrolysis and the oxidative burn off stages that occur during polymer breakdown These changes have been interpreted as being indicative of an extensive condensed phase action for the tin additive, in which the thermal breakdown of the polymer is altered to give increased formation of a thermally stable carbonaceous char at the expense of volatile, flammable products. The consequent reduction in the amount of fuel supplied to the flame largely accounts for the beneficial smoke-suppressant properties associated with zinc stannates and other tin-based fire retardants. 

Special considerations presence of zinc, copper, iron and nickel compounds accelerated dehydrochlorination combination of basic magnesium carbonate and aluminum hydroxide is used as flame retardant and smoke supressant chlorinated polyethylene adsorbs on the surface of titanium dioxide forming a layer 1-20 nm thick depending on the aciii/base interaction parameter of titanium dioxide ... 

Manufacturers of various fillers continue studies on altemative systems. Most antimony oxide used as a fire retardant can be replaced by a combination of zinc borate without the loss of other properties (in some cases improvements are reported). Another option is to use the same filler systems which are used in polyethylene insulated cables and wires. These are based on magnesium hydroxide and aluminum hydroxide. These systems pcrfoim as flame retardants but require a high filler concentration which affects jacket resistance and mechanical performance. Recently, new coated grades have been developed which can be used at up to 65 wt% without the loss of properties or productivity (extrusion rates 2,500 m/min of cable are possible). ... 

Some of the inorganic compounds, snch as antimony trioxide (Sb203), or boron-based componnds, snch as zinc borate, fnnction as synergists rather than directly as flame retardants bnt enhance the effectiveness of the latter. Antimony trioxide is used mainly with halogenated flame retardants. 

Flamtard S Tin zinc oxide (SnZnOs). Flame retardant for PVC, polychloroprene, chlorosulfonated polyethylene, polypropylene, other halopolymers. White powder d = 3.4 dec 180° soluble in strong acids and bases LDso (rat orl) > 5000 mgikg, (rat der) > 2466 mg/kg. Alcan Chem. Atomergic Chemetals Blythe, Williams Ltd, Joseph Storey. 

Uses Pigment, corrosion inhibitor, tannin stain blocker, flame retardant, UV stabilizer for use In water- and solv.-based coatings stabilizer for metals and metal salts, esp. zinc, for formulation in zinc-rich coatings food-contact paper/paperboard Features Multifunction ... 

Wang, D.-Y., Leuteiitz, A., Wang, Y.-Z. et al. (2010) Preparation and burning behaviors of flame retarding biodegradable poly(lactic acid) nanocomposite based on zinc aluminum layered double hydroxide. 

Traditionally, Zirpro -finished wool meets the above requirements and decabro-modiphenyl ether/antimony oxide-acrylic resin-fmished cotton fabrics (originally marketed as Caliban, White Chemical) have also been found to be suitable for workers in the aluminium industry. However, as discussed in Chapter 8, this latter finish is currently being withdrawn on environmental grounds and this whole area has recently been reviewed by Makinen, who lists more recent fabrics based on a variety of blends with flame retardant wool, viscose, and inherently flame retardant aramid fibres, for example. However, these factors are all different for molten iron or steel, copper, tin, lead, zinc, or aluminium and so protective aprons and overalls have to be tailored to fit the threat. Examples listed by Makinen for molten aluminium resistance include ... 

The active species in fire retarding are the halogens, chlorine and bromine, phosphorus, and water. The performance of these primary flame retardants is enhanced by synergists antimony, zinc and other metal salts. Some help to develop a protective char (e.g., phosphorus-based systems), separating the unbumed polymer from the flame and heat source. 

CHARMAX LS are zinc-molybdenum complexes targeted as smoke suppressants in PVC wire and cable, PVC plastisols and rigid PVC products. LS Z4A is used in a simple PVC jacket formulation. Aroimd 5% of such additives can replace up to 20% of AOM and reduce the afterglow sometimes seen with antimony oxide containing formulations. Also CHARMAX products are cheaper by weight than primary molybdenum and tin-based additives, AOM and zinc starmate, and lower loadings provide the required level of flame retardancy or smoke suppression that may be specified. The complexes may be used as partial of complete replacements for antimony oxides, whose price and supply has been unpredictable in recent times. 

DuPont have patented a flame retardant composition based on melamine pyrophosphate, with or without zinc borate, for use in a number of thermoplastic resins (US Patent 5859099). 

In the present chapter, we report some of om study on both raw and surface-modified Grewia optiva fiber-reinforced UPE matrix-based composites, which possess enhanced mechanical and physico-chemical properties when compared with UPE matrix. In addition to the effect of flame retardants, i.e., magnesium hydroxide and zinc borate, on flame resistance, the behavior of resulted Grewia optiva fiber-reinforced composites have also been evaluated and was foimd to be improved. A significant discussion on the work of other researcher s work has also been added in the chapter. 

For instance, the effect of smoke reduction and flammability performance of zinc-based compounds (i.e. zinc borate and zinc hydroxystannate) in epoxy resin composites used in the aerospace and aeronautical industries have been analyzed (Formicola et al., 2011). The flammability performance of neat and loaded systems was analyzed by using micro-combustion calorimetry, while smoke generation, in terms of CO and CO2 production, was analyzed under dynamic conditions by using cone calorimetry. The experimental results have shown that the dispersion of zinc borate and zinc hydroxystannate within epoxy matrices leads to a significant variation in flame retardant properties in particular the total heat release is reduced by about 25% and 30%, respectively, and the heat release capacity by about 30% and 50%, respectively. The system containing zinc hydroxystannate shows an enhancement in all smoke reduction properties, and both compounds lead to a reduction of the CO2/CO ratio. 

Fillers may promote char magnesium hydroxide, zinc borate, antimony oxides require high loadings and can degrade mechanical and other properties. Toxicity of antimony-based retardants is a concern. Can be used with other flame retardants synergistically. 

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