Magnesium hydroxide thermal stability

Reasons for use abrasion resistance, cost reduction, electric conductivity (metal fibers, carbon fibers, carbon black), EMI shielding (metal and carbon fibers), electric resistivity (mica), flame retarding properties (aluminum hydroxide, antimony trioxide, magnesium hydroxide), impact resistance improvement (small particle size calcium carbonate), improvement of radiation stability (zeolite), increase of density, increase of flexural modulus, impact strength, and stiffness (talc), nucleating agent for bubble formation, permeability (mica), smoke suppression (magnesium hydroxide), thermal stabilization (calcium carbonate), wear resistance (aluminum oxide, silica carbide, wollastonite)... 

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... 

There are a number of different origins for this product.3 First, there is a limited use of milled natural product (known as brucite), which is impure, less thermally stable than refined magnesium hydroxide and, depending on purity, is generally colored. This is suitable for some applications, where low cost is a requirement and color, and thermal stability are not critical. 

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. 

The water solubilities of M(OH)2 (M = Mg, Ca, Sr, Ba) increase down the group, as do their thermal stabilities with respect to decomposition into MO and H2O. Magnesium hydroxide acts as a weak base, whereas Ca(OH)2, Sr(OH)2 and Ba(OH)2 are strong bases. Soda lime is a mixture of NaOH and Ca(OH)2 and is manufactured from CaO and aqueous NaOH. Soda lime is easier to handle than NaOH and is commercially available, being used, for example, as an absorbent for CO2, and in qualitative tests for [NUi] salts, amides, imides and related compounds which evolve NH3 when heated with soda lime. 

Oyama HT, Sekikawa M, Shida S. Effect of the interface structure on the morphology and the mechanical, thermal, and flammability properties of polypropylene/poly(phenylene ether)/magnesium hydroxide composites. Polym Degrad Stabil 2012 97(5) 755-65. 

The main sectors for magnesium hydroxide use are in elastomers and thermoplastics, since they cause excessive thickening in the main thermoset application of unsaturated polyester systems. It is also much more expensive than ATH with which it shares comparable properties and flame retardancy, and so ATH will be preferred by processors wherever possible. As a result the principle opportunities are in applications where the extra thermal stability is essential, mainly in PP and polyamides. 

Martinswerk of Germany said that its Magnifm flame retardants have been specifically created for applications as flame retardant additives, compared with other magnesium hydroxides that have been manufactured from seawater with the pharmaceutical industry in mind. Magnifin is especially recommended for situations where low smoke emission and a high thermal stability are required from a halogen-free retardant. 

Several FR systems have come to the market from various sources. 58% are halogenated products preferred for their better thermal stability. 42% are non-halogenated t5q)es used when a high CTI is specified these can be broken down into 22% red phosphorus products, 16% melamine cyanurate and the remaining 4% of magnesium hydroxide. 

It has been observed from the above discussion that mechanical, physico-chemical and fire retardancy properties of UPE matrix increases considerably on reinforcement with surface-modified natural cellulosic fibers. The benzoylated fibers-reinforced composite materials have been found to have the best mechanical and physico-chemical properties, followed by mercerized and raw Grewia optiva fibers-reinforced composites. From the above data it is also clear that polymer composites reinforced with 30% fibers loading showed the best mechanical properties. Further, benzoylated fibers-reinforced composites were also found to have better fire retardancy properties than mercerized and raw fibers-reinforced polymer composites. Fire retardancy behavior of raw and surface-modified Grewia optiva/GPE composites have been found to increase when fire retardants were used in combination with fibers. This increase in fire retardancy behavior of resulted composites was attributed to the higher thermal stability of magnesium hydroxide/zinc borate. 

Magnesium hydroxide is a white crystalline material, with similar flame-retardant properties to ATH but with superior thermal stability. Until recently, commercial interest in its use as a flame-retardant filler was minimal outside Japan. This is because the only products generally available were either of poor quality or expensive. 

The use of magnesium hydroxide in polyamides is restricted by the low degradation temperature and the low hydrolytic stability of polyamides. Polyamide 6 and 6.6 begin to degrade at around 350°C whereas magnesium hydroxide releases water between 320 and 440°C. In situ production of water lowers the thermal stability of polyamides. The addition of 60 wt% magnesium hydroxide produced a flame... 

L. Haurie, A. Ferndndez, J. Velasco, J. Chimenos, J. Lopez Cuesta, and F. Espiell, Thermal stability and flame retardancy of LDPE/EVA blends filled with synthetic hydromagnesite/aluminium hydroxide/montmorillonite and magnesium hydroxide/ aluminium hydroxide/montmorillonite mixtures. Polymer Degradation and Stability, 92 (2007), 1082-7. 

P. R. Hornsby, J. Wang, R. Rothon, G. Jackson, G. Wilkinson, and K. Cossick, Thermal decomposition behaviour of polyamide fire-retardant compositions containing magnesium hydroxide filler. Polymer Degradation and Stability, 51 (1996), 235-49. 

Additives used in final products Fillers aluminum hydroxide, calcium carbonate, clay, carbon nanotubes, magnesium hydroxide, montmorillonite, red phosphorus, quartz, silica, wood fiber, zinc oxide, zinc powder Plasticizers EVAC is used as plasticizer in PVC and PLA therefore it seldom requires plasticization Antistatics 2-methyl-3-propyl benzothiazolium iodide, alkylether triethyl ammonium sulfate, organic amide Antiblocking tty amide, laponite, silica Release methylstyryl silicone oil Slip eru-camide, oleamide, stearamide Thermal stabilizer BHT ... 

The thermogravimetric analysis was conducted in order to determine the effect of surface modification of magnesium hydroxide on the thermal stability and the depending function on the magnesium hydroxide mass loss with increasing temperature (Table 4.3... 

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