One reason magnesium stearate can be used as a lubricant is its platy crystal shape. These platy crystals are layered and are separated during mixing, coating individual particles or equipment surfaces. While layered platy crystal shapes are common, round or even needle shapes exist. The trihydrate is a needle-shaped particle, and its lubricity is significantly reduced compared to other particle morphologies. It should be noted that all forms of magnesium stearate can be converted to trihydrate under high humidity conditions.

　　Commercial batches of magnesium stearate are a mixture of amorphous and crystalline hydrates. After absorbing moisture under ambient humidity, the anhydrous material has a water content of 3%~4%, with most of the water weakly bound within the lattice. The anhydrous material will show significant hygroscopicity at relative humidity above 80%. Pharmacopoeias stipulate that the loss on drying of magnesium stearate is less than 6%, and changes in loss on drying may lead to decreased lubricity.

　　The bulk density of commercial grade magnesium stearate is generally between 0.15g/cm3 and 0.30g/cm3. Using magnesium stearate with a 2-fold difference in this bulk density as a lubricant may result in different final products. You can use the tapped density to determine the particle size and specific surface area of magnesium stearate (generally, the finer the particle size, the larger the specific surface area, and the smaller the tapped density).

　　Another property that affects the lubricating function of magnesium stearate is the specific surface area. The larger the specific surface area, the better the lubricity. Under certain conditions of mixing and tableting, the larger the specific surface area of magnesium stearate, the lower the tensile strength of the tablets, the higher the friability, and the slower the dissolution and disintegration. The specific surface area of magnesium stearate on the market is typically between 5~20m2/g, which is a considerable range. Some variations may be attributed to the method of sample preparation and testing. Specific surface area data should be determined at several different relative pressures (i.e., multipoint method). Suppliers usually set the upper limit of the specific surface area to twice the lower limit (e.g., 6~12m2/g). While variations within this range may not affect all products, they may affect products that are easily over-lubricated.

Magnesium Stearate (MS)

Packaging Specifications:10kg/bag

Quality Standard:CP2020 USP Current Edition

Main Uses:This product has lubricating, anti-adhesive, and flow-aiding properties. In pharmaceutical preparations, it is mainly used as a lubricant, glidant, or anti-adhesive agent for tablets and capsules.

Magnesium stearate, with the chemical formula C36H70MgO4 and a molecular weight of 591.24, is an organic compound. It is a fine, white, non-gritty powder with a slippery feel when in contact with the skin. It is insoluble in water, ethanol, or ether. Magnesium stearate is mainly used as a lubricant, anti-adhesive agent, and glidant. It is particularly suitable for granulation of oily and extract-containing drugs, producing granules with good flowability and compressibility. It is used as a glidant in direct compression. Magnesium stearate can also be used as a filter aid, clarifying agent, and foaming agent, as well as a suspending agent and thickening agent in liquid preparations.

Magnesium Stearate Synthesis Methods

1. Preparation of Sodium Stearate: Dissolve 4.25 parts of sodium hydroxide in 50 parts of water and heat to 85℃. Add 25 parts of stearic acid to the reaction kettle, add 500 parts of water, and dissolve with stirring. Adjust the temperature to 85～90℃. Add the prepared sodium hydroxide solution slowly to the stearic acid aqueous solution with stirring, maintaining the temperature at 75～80℃. React with stirring until the end point. Keep the product sodium stearate solution warm for later use.

Preparation of Magnesium Stearate: Dissolve 15 parts of magnesium sulfate in 150 parts of water, heat to 55℃, and slowly add to the prepared sodium stearate solution. Carry out a metathesis reaction with stirring. The magnesium stearate produced precipitates as a solid. After the reaction is complete, allow to stand to separate the clear liquid, then wash with water, centrifuge to dehydrate, and dry at 80～85℃ to obtain the finished product.

2. Neutralize 46.6g of stearic acid with 164mL of 1mol/L sodium hydroxide solution to obtain 50g of sodium stearate in 2L of water. Heat the obtained sodium stearate solution to 80℃ and add dropwise a solution prepared by dissolving 20g of magnesium chloride in 100mL of water. After continuous stirring, a white precipitate quickly precipitates. After cooling, filter, wash with water until no chloride ions are present, and finally wash with ethanol. Place 10g of the product in a vacuum desiccator containing concentrated sulfuric acid for 4 weeks to obtain the product Mg(C18H35O2)2·2H2O. Dissolve the remaining product in benzene and reflux for 20min. Pour out the upper yellow liquid layer while hot and evaporate to dryness. The solid obtained can be recrystallized from benzene to obtain the product Mg(C18H35O2)2.