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Stearic acid is a common saturated fatty acid, chemically known as "octadecanoic acid", with the molecular formula C₁₈H₃₆O₂. At room temperature, it appears as a white or pale yellow waxy solid with no distinct odor. It is soluble in organic solvents such as oils, alcohols, but insoluble in water.

It is widely found in nature (such as in animal fats, vegetable oils, and cocoa butter), and can also be extracted or synthesized through industrial processing. Its core application lies in serving as a functional component, playing roles such as stabilization, lubrication, and emulsification in fields like daily chemicals, medicine, food, and industry.

In the field of daily chemical and skin care: It is a core matrix component of skin care products such as face cream, lotion, and hand cream. Its property of melting upon heating and solidifying upon cooling helps the products form stable and uniform paste or emulsion forms, preventing oil and water from separating. It can also adjust the skin feel, forming a light film layer on the skin surface when applied, providing a smooth and non-sticky usage experience and reducing the heavy feeling. In soap manufacturing, it can undergo saponification reaction with alkali to generate cleaning components, making the soap harder and more durable, and assisting in cleaning skin oil and dirt.

In the field of medicine: It mainly functions as a pharmaceutical excipient. When making tablets or capsules, it can adhere to the surface of drug powder particles, reducing particle friction and facilitating the smooth pressing and shaping of the powder, preventing adhesion to the mold, and making the tablet surface smoother. In topical ointments, as an oil phase matrix, it helps evenly disperse the active ingredients of the drug and forms a closed layer on the skin surface, reducing water evaporation and assisting in the penetration and absorption of the drug. In some sustained-release tablets, it can also serve as a sustained-release material to control the dissolution rate of the drug and extend the duration of the drug effect.

In the field of food (mostly used in the form of stearates): It is commonly used as an anti-caking agent, added to powdered foods such as milk powder, protein powder, coffee powder, and seasonings, adhering to the surface of the powder particles to reduce adhesion, prevent food from clumping due to humidity or pressure, and facilitate pouring and mixing. It can also be used as an emulsifier in foods such as chocolate, ice cream, and margarine, helping to evenly mix oil and water components, preventing chocolate from developing a white film on the surface and ice cream from separating after melting, and enhancing the smooth and delicate texture of the food.

In the industrial field: In rubber production, it can accelerate the vulcanization reaction of rubber (helping liquid rubber transform into elastic solid), reduce the friction between rubber and molds for easier demolding, and also soften rubber to improve its flexibility. In the processing of PVC plastics (such as pipes, films, and toys), it can absorb harmful gases produced at high temperatures to prevent plastic degradation and brittleness, and act as a lubricant to reduce the friction between plastic melt and equipment, facilitating molding and making the surface of the finished product smoother. In the textile industry, it can adhere to the surface of cotton, synthetic fibers, and other fibers, reducing fiber friction and making the fabric softer and smoother, and can also be used as a finishing agent to enhance the luster and stiffness of the fabric.