Stearates as lubricants

Cellulose powder is now stirred into the cooled solution until the mass can still just be stirred.The contents of the flask are then transferred to a large beaker and more cellulose powder is kneaded in by hand (wear rubber gloves ) until a total of 35 g has been added.The crumbled mixture is dried for 24 h at 50 °C in the vacuum oven. Finally, the dried product is finely ground in a mortar, mixed with 1% of ammonium chloride and 1 % of zinc stearate (as lubricant) and crosslinked (cured) by heating to about 160 C for 10 min in a simple press at 300-400 bar. A thin transparent plate is obtained that is no longer soluble in or attacked by water this is more convincing if a small piece is allowed to stand overnight in a beaker of water. 

NIR was used to determine the effects of changes in magnesium stearate concentration and variations in compression pressure on tablet analysis. Various types of Avicel (microcrystalline cellulose), varying mostly in particle size, were compressed into tablets with or without magnesium stearate as lubricant by using various compression pressures. Various mathematical treatments were used to either measure the differences or obviate their effects on the analysis. 

The Novolak obtained is used to fabricate a molding by mixing with sawdust and hexamethylenetetramine as follows 12.5 g of finely ground Novolak, 12.5 g of dry sawdust, 1.75 g of hexamethylenetetramine, 0.5 g of magnesium oxide (to trap residual acid from the condensation), and 0.25 g of calcium stearate (as lubricant) are thoroughly mixed (best in a ball mill or analytical mill) and then heated in a mold at 140 bar for 5 min at 160°C. The resulting molding is infusible and insoluble. 

The packing density may be sharply raised by adding zinc stearate as lubricant (0.3-1% of the mass of the powder) [450]. 

More than half the metal stearates produced in the United States are appHed as lubricants and heat stabili2ers (qv) in plastics, particularly in the processing of poly(vinyl chloride) (PVC) resins. 

Normal and dibasic lead stearate have a stabilising effect but their main uses are as lubricants (see section 12.5.4). Lead silicate is sometimes used in leathercloth formulations but is today of little importance. Other lead compounds now of negligible importance are coprecipitated lead orthosilicates and lead salicylate. 

Stearic acid and metal stearates such as calcium stearate are generally used as lubricants at a rate of about 1-3% on the total compound. Waxes such as camauba and ceresin or oils such as castor oil may also be used for this purpose. 

Metal stearates such as zinc, magnesium or aluminium stearates are commonly used as lubricants at about 1 % concentration. Other materials that have been used successfully include oxidised paraffin wax and sulphonated castor oil. 

Metallic soaps such as zinc stearate or calcium stearate are used as lubricant, which reduces the friction coefficient of the surface of the thermosensitive layer resulting in smooth running on recording machines. 

In the mid-70s, it was a generally expressed opinion that there could be as many as 100 formulation factors that might affect bioavailability or bioequivalence. In fact, most of the documented problems centered around the use of the hydrophobic magnesium stearate as a lubricant or use of a hydrophobic shellac subcoat in the production of sugar-coated... 

A major use is as hthium stearate for lubricating greases. It makes a sohd grease that can withstand hard use and high temperatures. 

Hanssen, D., Ftihrer, C., and Schaefer, B. (1970), Evaluation of magnesium stearate as tablet lubricating agent by electronic pressure measurements, Pharm. lnd., 32(2), 97-101. 

Disintegration time, crushing strength, and friability of tablets, produced from Cop-MC using magnesium stearate as a lubricant, were found to be independent of the particle size of the prepared granules (Fig. 2.46). 

Metal stearates, such as magnesium or calcium stearate that serve as lubricants in conventional tablets, are seldom used as intrinsic lubricants in connection with effervescent tablets due to their insolubility in water. Use of stearates results in an undissolved, foamy, soapy-tasting layer on the surface of the cloudy solution. In addition, normal lubricant concentrations of metal stearates make the tablets hydrophobic, which entails a slow dissolution of the effervescent tablet in the water. However, very low concentrations of metal stearates can be used to improve the rate of solution of effervescent tablets as the tablet will remain immersed in the water during dissolution and not float to the surface the way a tablet without metal stearate would. A floating tablet presents a smaller surface area to the water than a tablet immersed in the liquid. 

Johansson ME. Granular magnesium stearate as a lubricant in tablet formulations. Int J Pharm 1984 21 307—315. 

Fatty acid esters, because of the great variety of molecular structures that are possible, offer great versatility to the plastics compounder. Liquid fatty acid esters of short-chain monofunctional alcohols have a distinct secondary plasticizer action, whereas fatty acid esters of long-chain fatty alcohols like stearyl stearate or cetyl palmitate are well known as wax esters and because of their thermal stability, good flow properties and resistance to plate out are broadly used as lubricants for PVC and other polar plastics. 

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