Chemistry name: Magnesium stearate

CAS No.: 557-04-0

EINECS No.: 209-150-3

Chemical formula:  C36H70MgO4

Molecular mass: 591.24 g/mol

Definition:

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EXCfiller®Magnesium stearate is a compound formed from the combination of stearic acid and magnesium ions, and is a type of fatty acid salt. Appearing as a white, odourless and tasteless fine powder with a typical particle size of 1-10 μm, it has a slippery texture. It is the most widely used multifunctional excipient in the food, pharmaceutical and cosmetics industries, with its core functions centred on three primary areas: lubrication, anti-caking and emulsification.

■ Source

TThe core raw materials used to produce EXCfiller®Magnesium stearate are stearic acid and magnesium salts. The purity of these raw materials directly affects the quality of the finished product. Stearic acid is a long-chain saturated fatty acid (C18). In industry, it is often used in the form of 'mixed fatty acids' (containing a small amount of palmitic acid (C16), typically with a stearic acid content of at least 40% and a palmitic acid content of no more than 60%). Based on its source, stearic acid can be categorised into three types. Plant-based stearic acid (the most common choice) is derived from vegetable oils, such as palm oil, coconut oil and soybean oil, via hydrolysis and fractionation. Animal-derived stearic acid uses fats from animals, such as butterfat, lard and tallow, as raw materials which are processed through hydrolysis and refining. Blended stearic acid combines plant-based and animal-derived stearic acids in a specific ratio (e.g. 7:3) to balance cost and performance. With a stearic acid content of at least 50%, it is suitable for mass-market products without specific sourcing requirements. Magnesium salts used in the production of food/pharmaceutical-grade magnesium stearate must meet requirements for high purity and low impurity levels. Common types include magnesium hydroxide, magnesium oxide, and magnesium carbonate.

Particularities of EXCfiller®Magnesium stearate:

Product Specifications:

EXCfiller®Magnesium stearate is available in the following specification and contents:

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☑ EXCfiller®Magnesium stearate ≥45.0% (Stearic Acid), ≥90.0%(Relative Content of Stearic Acid and Palmitic Acid)

Product quality standards:

● USP, EP, BP, CP, Food grade, In-house

EXCfiller®Magnesium stearate Applications:

EXCfiller®Magnesium stearate is the most widely used lubricant excipient in pharmaceutical formulations. It is distinguished by its superior lubricity, excellent biocompatibility, stable physicochemical properties and non-allergenic nature. It provides anti-caking and flow-enhancing properties, making it suitable for various dosage forms, including oral solid preparations and topical formulations. It is particularly indispensable in direct compression tableting processes.

Oral solid dosage forms, including tablets, capsules and granules, are the most critical application scenario. In tablets, the core functions are lubricants (primary function), anti-caking agents (secondary function) and flow aids (synergistic function). These reduce friction between drug particles and between particles and tableting punch dies, minimising the risk of sticking, cracking and delayed disintegration. They prevent drug powders from adhering to punch surfaces, ensuring smooth tablet surfaces and consistent weight. They also enhance powder flowability, improve mixing uniformity and boost tableting efficiency. For capsules (hard and soft), the core functions include flow aids and lubricants for hard capsules, and emulsifying stabilisers for soft capsule fillings. Hard capsule filling requires ≥95% uniformity when mixing the drug powder with magnesium stearate, a filling rate of ≥1000 capsules per minute and fill weight variation of ≤±3% (with an average fill weight of ≤0.3 g). For soft capsule fillings, the contents are prepared by mixing magnesium stearate with drug particles and vegetable oil. High-speed stirring (1000-1500 rpm) ensures the mixture is uniformly suspended (settling volume ratio ≥0.95) and prevents stratification within the capsule. The core functions of granules (oral granules) are anti-caking agents and flow enhancers. Blended externally after granule drying. Post-blending, the flowability of the granules increases by ≥30% and the angle of repose is ≤35°, with no significant caking observed after six months of storage. Topical formulations (ointments, creams, suppositories) primarily function as emulsifying stabilizers + emollients.

​​​​​​​The core application of food-grade EXCfiller®Magnesium stearate is its multifunctional adaptability. By adjusting parameters such as particle size, magnesium content and acid value, it can be used as an anti-caking agent, lubricant, emulsifier and release agent. It also aligns with clean label trends, such as being derived from natural sources and being residue-free, and it can be used in various food forms, including powders, solids, and semi-solids. In powdered foods, its primary functions are as an anti-caking agent and a flow enhancer. In baked goods, its primary roles are release agent, lubricant and anti-staling agent. In confectionery and chocolate, its key functions are emulsifying stabiliser, release agent and anti-caking agent. In dairy products, its core functions are an anti-caking agent for milk powder and a stabiliser for yoghurt and ice cream.

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■ Production technology characteristics

There are two main production processes for magnesium stearate: the aqueous method (wet process) and the dry method (melting process). The aqueous method is the mainstream process for food/pharmaceutical-grade products due to its high product purity and low impurity levels. The dry method is predominantly used for industrial-grade products or lower-end food-grade products. The aqueous method is the predominant process (preferred for food and pharmaceutical grades) and involves stearic acid undergoing a neutralisation reaction with magnesium salts in an alkaline environment to form magnesium stearate precipitation. The product is then purified, dried and milled to obtain the final material. The secondary process is dry-method production (for industrial-grade or low-end food-grade applications). This involves mixing solid powdered stearic acid with solid powdered magnesium salt in a specific ratio, then subjecting the mixture to a melt reaction at a high temperature (120-150 °C) to form magnesium stearate. The resulting product is then cooled, ground and processed into its final form.