Flame retardants magnesium

One of the shortcomings most adversely affecting the utilization of PP filled with flame retardant magnesium hydroxide (Mg(OH)2) is the steep reduction of subambient fracture toughness compared with that of neat polypropylene. Generally, an increase in the resistance to crack initiation and growth can be achieved... 

Flame letaidancy can be impaited to plastics by incorporating elements such as bromine, chlorine, antimony, tin, molybdenum, phosphoms, aluminum, and magnesium, either duriag the manufacture or when the plastics are compounded iato some useful product. Phosphoms, bromine, and chlorine are usually iacorporated as some organic compound. The other inorganic flame retardants are discussed hereia. 

F. Molesky in Recent Advances in Flame Retardamy of Polymeric Materials, Stamford, Coim., 1990 F. Molesky, "The Use of Magnesium Hydroxide for Flame Retarded Low Smoke Polypropylene," Polyolefins IHInternational Conference, Feb. 24,1991, Houston, Tex. 

Uses. The principal use of magnesium hydroxide is in the pulp (qv) and paper (qv) industries (52). The main captive use is in the production of magnesium oxide, chloride, and sulfate. Other uses include ceramics, chemicals, pharmaceuticals, plastics, flame retardants/smoke suppressants, and the expanding environmental markets for wastewater treatment and SO removal from waste gases (87). 

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. 

The performance of aluminium hydroxide/magnesium hydroxide-filled systems can be enhanced by incorporation of zinc hydroxystannate in halogen-free rubbers giving reduced smoke and toxic gas emission, coupled with higher flame retardancy. This action will be complimentary to the water release and endothermic effects of aluminium hydroxide/magnesium hydroxide filler systems. 

Hitachi Cable Ltd. (35) has claimed that dehydrogenation catalysts, exemplified by chromium oxide—zinc oxide, iron oxide, zinc oxide, and aluminum oxide—manganese oxide inhibit drip and reduce flammability of a polyolefin mainly flame retarded with ATH or magnesium hydroxide. Proprietary grades of ATH and Mg(OH)2 are on the market which contain small amounts of other metal oxides to increase char, possibly by this mechanism. 

Magnesium hydroxide is very basic (high pH) and will degrade PET and PBT if it is used as a flame retardant [39],... 

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. 

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. 

The traditional flame retardant is based on organobromine compounds together with antimony trioxide as a synergist. Magnesium hydroxide is a good flame retardant due to its high decomposition temperature and smoke suppression properties. It is widely used in thermoplastic materials. However, magnesium hydroxide must be added in portions of some 60% to achieve a reasonable effect. 

S. Chang, T. Xie, and G. Yang, Effects of polystyrene-encapsulated magnesium hydroxide on rheological and flame-retarding properties of HIPS composites, Polym. Degrad. Stab., 91(12) 3266-3273, December 2006. 

Flame retardant - [ALUMENUMCOMPOUNDS - ALUMINUM SULFATE AND ALUMS] (Vol 2) - [AMMONIUMCOMPOUNDS](Vol2) - [VINYL POLYMERS - VINYL CHLORIDE POLYMERS] (Vol24) -ethyleneimines [IMINES, CYCLIC] (Vol 14) -filler for [LEAD COMPOUNDS - LEAD SALTS] (Vol 15) -iron compounds as [IRON COMPOUNDS] (Vol 14) -magnesium hydroxide as filler [MAGNESIUMCOMPOUNDS] (Vol 15)... 

Aluminum bromide AlBr3 is used as a catalyst and parallels AICI3 in this role. Strontium and magnesium bromides are used to a limited extent m phamiacentical applications. Ammonium bromide is nsed as a flame retardant in some paper and textile applications potassium bromide is used in photography. Phosphorus tribromidc PBr3 and silicon tetrabromide SiBi4 are nsed as intermediates and catalysts, notably in the production of phosphite esters. 

To improve the fire retardancy of polypropylene, beyond the UL 94 V-2 level, it is necessary to use blends of aromatic bromine fire retardants with antimony trioxide as a synergist. The usual loading is between 35% and 40% fire retardant however, the additional cost may prohibit commercialization. Moreover, the presence of aromatic bromine increases the photooxidation of polypropylene67 69 inactivating hindered amines. To reduce the cost without losing in efficacy the combination of brominated flame-retardant/antimony trioxide system with magnesium hydroxide... 

Montenzin, F. Lopez-Cuesta, J. M. Crespy, A. Georlette, P. Flame retardant and mechanical properties of a copolymer PP/PE containing brominated compounds/antimony trioxide blends and magnesium hydroxide or talc, Fire and Materials, 1997, 21(6), 245-252. 

By reacting aluminum hydroxide with oxalic acid, basic aluminum oxalate can be produced, which is thermally stable to 330°C, losing 51% of its mass on decomposition at temperatures above 450°C. It is reported to have a flame-retarding and smoke-suppressing action similar to ATH, but because of its increased thermal stability, it can be used in polyamides and thermoplastic polyesters. However, unlike magnesium hydroxide, in these polymers it does not cause hydrolytic degradation.2... 

These are a series of magnesium aluminum hydroxycarbonates with varying magnesium to aluminum ratios between 1.5 and 3.0g-atoms of magnesium to 1 g-atom of aluminum. They have layers of magnesium hydroxide interspersed with aluminum cations and carbonate anions. They show similar flame-retardant activity and thermal stability to ATH, but their higher cost currently limits their potential use. 

Metal hydroxides in combination with various silicon-containing compounds have been used to reduce the amount of additive required to achieve a required level of flame retardancy in a variety of polymeric materials, including polyolefins.62-63 Systems that have been used contain a combination of reactive silicone polymers, a linear silicone fluid or gum, and a silicone resin, which is soluble in the fluid, in addition to a metal soap, in particular magnesium stearate. However, there is little insight given into how these formulations work. 

The combination of melamine with hydrated mineral fillers can improve the fire retardancy behavior of PP, eliminating at the same time the afterglow phenomenon associated with these fillers used in isolation.70 Similarly in EVA copolymer, antimony trioxide used in combination with metal hydroxides has been reported to reduce incandescence.56 Chlorinated and brominated flame retardants are sometimes used in combination with metal hydroxides to provide a balance of enhanced fire-retardant efficiency, lower smoke evolution, and lower overall filler levels. For example, in polyolefin wire and cable formulations, magnesium hydroxide in combination with chlorinated additives was reported to show synergism and reduced smoke emission.71... 

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