What is magnesium stearate?

Magnesium stearate, also known as magnesium octadecanoate, is the magnesium salt of stearic acid fatty acid. It is often used as a lubricant in tablets, capsules, and powders.
Stearic acid, the raw material for the production of magnesium stearate, is a mixture of stearic acid and palmitic acid. The ratio of the content of these two substances will affect the quality of magnesium stearate.
Magnesium stearate has a significant role in the production of formulations, although in small quantities. Its properties include the following 3: anti-adhesive, flow-enhancing, and lubricating. Many products with the use of magnesium stearate may need better particle flow, sticky punch, and astringent punch when pressing tablets.
In some research and production, people found that, in addition to serving as a lubricant, the addition of magnesium stearate also produces a particular softening effect on tablets, which is mainly manifested as a substantial reduction in the hardness of tablets.
Precautions for the use of magnesium stearate precautions for the use of magnesium stearate
Magnesium stearate is a widely used pharmaceutical excipient in the pharmaceutical industry and is usually considered non-toxic when taken orally. However, large oral doses can cause diarrhea or mucosal irritation. Magnesium stearate adheres easily to the skin, so you should take care to protect yourself in daily experiments by wearing gloves, masks or goggles, and lab coats. Excessive inhalation of magnesium stearate dust will cause upper respiratory discomfort, coughing, and asphyxiation, so it should be operated in a ventilated place, and dustproof respiratory equipment should be worn.
Magnesium stearate is contraindicated with strong acids, strong bases, and iron salts. Mixing with substantial oxides should be avoided. Magnesium stearate should not be used in products containing aspirin, some vitamins, and most alkaloid salts.
 

Lubricating Mechanisms of Magnesium Stearate

Typically, there are four lubrication mechanisms: hydrodynamic lubrication, elastohydrodynamic lubrication, mixed lubrication, and boundary lubrication. The first three lubrication mechanisms are related to the use of liquid lubricants to some extent. In the pharmaceutical industry, the most commonly used mechanism is the boundary lubrication mechanism.
Boundary lubrication usually means that the lubricant forms a film between two particle surfaces to reduce friction.
Structurally, the lubricants that produce boundary lubrication are usually long chain molecules with reactive end groups, such as stearic acid and its metal salts.
From a microscopic point of view, it is generally believed that the lubricating effect of magnesium stearate is due to the polar metal portion of the molecule adhering to the surface of the powder or particle. In contrast, the non-polar hydrocarbon portion of the molecule directionally discharges from the surface of the particle to the surface of the neighboring powder, particle, or piece of equipment (e.g., a press punch or capsule-filling machine punching rod), thereby achieving lubrication.
From a macroscopic point of view, one of the reasons magnesium stearate can be used as a lubricant is because of its lamellar crystal structure, where the layers are separated from their overlapping state during mixing, and due to its small particle size, it can be semi-continuously applied to individual particles or equipment surfaces. In the process of tablet pressing or filling, the magnesium stearate on the surface of the particles can be combined with the surface of the mold to form a film between the drug particles and the mold, reducing the friction between the mold and the drug particles and tablets in the process of moving to achieve the effect of lubrication.

Magnesium stearate affects the material compressibility of a variety of factors.

Magnesium stearate affects the compressibility of excipients by a variety of factors, such as mixing time, magnesium stearate dosage, excipient particle size, magnesium stearate particle size, mixing shear force, and other factors that affect the excipient's tableting properties.

1) Dosage, mixing time

A mixing time of magnesium stearate that is too long will lead to excessive lubrication and reduce the compressibility of the material. In contrast, the hydrophobic magnesium stearate will affect the capillary action of water, preventing water from penetrating the core of the tablets and leading to slower disintegration and dissolution. In some cases, the reduced dissolution rate caused by the action of magnesium stearate can be resolved by adding a high swelling disintegrant to the prescription.
During the mixing of solid particles with magnesium stearate, the magnesium stearate powder first forms a uniform adsorbed film on the surface of the particles in an adsorption-like manner.
Upon continued mixing, the magnesium stearate that is uniformly distributed on the surface of the particles may then delaminate or de-agglomerate, breaking up the magnesium stearate particles adsorbed on the surface of the particles and resulting in an increase in the coverage of the surface of the particles by the magnesium stearate.
With increasing mixing time, the coverage will be maximized when the magnesium stearate particles are monolayered on the surface of the particles.
The amount of magnesium stearate coverage on the surface of the particles can change the properties of the surface of the particles, which in turn can affect the apparent and intrinsic properties of the particles.
In subsequent tableting or capsule filling processes, since magnesium stearate is hydrophobic, more excellent surface coverage will result in greater hydrophobicity for the particles, and therefore, increased mixing time will result in delayed dissolution and disintegration when magnesium stearate is used as a lubricant.
In the development of the prescription process, it is necessary to choose the appropriate type of magnesium stearate, dosage, mixing time, and optimal mixing speed to protect the lubrication effect while preventing excessive lubrication so that the product is safe, effective, and quality-controlled.

2) Particle size and specific surface area

As the primary mechanism of magnesium stearate is to form a film on the surface of the particles, the coverage of magnesium stearate on the surface of the particles affects the lubrication effect. Also, it affects the nature of the particles and the subsequent process.
The specific surface area of magnesium stearate in the range of particle sizes below 10um shows a clear trend of increasing as the D50 (median particle size) decreases, and this trend is even more pronounced as the mixing concentration increases.
The specific surface area has a significant influence on the distribution of magnesium stearate on the particle surface. The larger the specific surface area of magnesium stearate, the stronger its polarity and the more excellent its adhesion, which can form a thin but uniform layer of magnesium stearate on the surface of the particles, while magnesium stearate with a lower specific surface area is easy to enrich on the surface of the particles.
This significant correlation between the particle size and specific surface area of magnesium stearate leads to the fact that the particle size of magnesium stearate affects the particular surface area of magnesium stearate, which affects the lubrication effect and, ultimately, the properties of the particles and the final product.

Magnesium stearate supplier

Luoyang Trunnano Tech Co., Ltd (TRUNNANO) is a professional Magnesium stearate powder supplier with over 12 years experience in chemical products research and development. 
We accept payment via Credit Card, T/T, West Union and Paypal. Trunnano will ship the goods to customers overseas through FedEx, DHL, by air, or by sea.

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