Aluminium Stearate - Overview
Aluminium Stearate or (aluminum tristearate) is a white coloured powder, wax – like powder (metallic soap) that dissolves well in vegetable oils upon heating. It is soluble in glycol, alkali, BTX, chlorinated hydrocarbons. If aluminium stearate is in high concentration, gelling can be seen upon cooling. It exhibits the following properties: good gelling and thickening action, excellent water repellence, transparency and a synergistic effect with zinc stearate or calcium stearate. Aluminium stearate exhibits a relatively high solubility in hydrocarbon solvents (such as mineral spirits) when compared to other metallic stearates. It is insoluble in water, alcohol and ether; but when hot, it is readily soluble in benzene, acids and common solvents.
Aluminium distearate is the most commonly used grade of aluminum stearate. It is used as a thickener in paints, inks and greases; a water repellent for leather and rope; and a lubricant in plastics and rope. It is also used in cement production for waterproofing and air entrainment, and in hot-melt paper coating compounds. Because of its unusually heavy bodying properties, aluminum monostearate is used in the manufacture of paints, inks, greases, and waxes. In recent years, hydrophobic aluminum monostearate was tested as a low-solubility denitrification substrate for anaerobic bacteria and a source of aluminum for phosphate precipitation. Aluminum stearate has potential for use in a flow-through container for denitrification of oxidized effluent from home sewage systems. It was also referred that the preheated mixture of metal soaps, along with the costabilizer, delayed the fast blackening of the polymer, but mainly showed a reduction.
Aluminium stearate is synthesised via the precipitation process using high quality stearic acid. This is done by adding aluminium isopropoxide to stearic acid in anhydrous pyridine, inducing the precipitation of the pyridine complex. Pyridine is then removed under vacuum to give the aluminium stearate. Aluminium stearate is a fine, bulky, odourless and colourless powder forming a plastic mass when heated, having the properties both of organic and inorganic matter. It embraces most of the characteristics of other metallic stearates and is regarded as the most important of these. Several studies of the material have already appeared in past years.
The Uses of Aluminium Stearate
Metallic stearates, which have been used primarily as acid scavengers, lubricants and release agents by the plastics industry, are becoming increasingly important in melt processing. In addition to optimizing production, the use of metallic stearates allows the processor to produce finished articles with smoother surfaces and lower friction. Metallic stearates are mainly produced from organic raw materials. Therefore, they tend to degrade to some degree when exposed to excessively high temperatures, resulting in discoloration. Fanchem has developed a range of thermostable metallic stearates, which are highly resistant to discoloration when used in transparent or brightly colored thermoplastics even at high processing temperatures
Aluminium stearate is used as an emulsifier in cosmetics. They are used for their lubricating properties. The stearate salts also increase the thickness of the oil portion of cosmetics and personal care products. Hence, finished cosmetics products are typically not transparent.
Aluminium stearate is used as a thickener in Varnishes/Lacquers, an anti-settling agent for pigmentation, as a pigment suspension, and an agent to improve water resistance and gloss. It is useful as a water repellent agent, a hydrophobic agent, and a waterproof agent in the paint industry.
|IUPAC Name||Aluminium octadecanoate|
|Molecular Weight||844.41 g mol-1|
|Melting Point||°C||150 (min)|
|Free Fatty Acids||%||4.0 (max)|
|Solybility in Water||Insoluble|
|Stability||Stable under ordinary conditions|