
Stearic acid is the most common saturated fatty acid in nature, a waxy white solid that does not have a characteristic odor. Its chemical formula is CH3(CH2)16COOH. It is most commonly found in vegetable and animal fats. Salts and esters of stearic acid with the general formula C17H35COOR, where R = metal, UV radical, are called stearates. Derived from animal (up to 30%) and vegetable fat (usually <5%), the substance is widely used as a lubricant and as an additive in industrial products. Stearic acid is used in the production of metal stearates, pharmaceuticals, soaps, cosmetics and food packaging.
The molecule of stearic acid: carbon atoms are depicted in black, hydrogen — white, oxygen — red
Properties of stearic acid
It is a colorless and odorless substance. It is insoluble in water, but soluble in esters. It reacts with alkalis to form stearates. Stearic acid undergoes typical acid reduction reactions to alcohols and esterification reactions by a number of alcohols.
Density |
0.9408 g/sm³ (20 °C) 0.847 g/sm³ (70 °C) |
Boiling temperature | 361 °C |
Melting temperature | 69.3 °C |
Solubility | Alkyl acetates, alcohols, methyl formate, phenols, carbon disulfide CS2, carbon tetrachloride CCl4 |
The stearic acid molecule has a bifunctional diphilic structure with a polar COO- group, which can be attached to metal cations, and a nonpolar hydrocarbon chain, which provides solubility in organic solvents. Stearic acid has found its application as a surfactant used to stabilize suspensions and other dispersion media, polymers due to this structure. The polar group of the molecule, due to its ability to interact with water, is immersed in it, and the UV radical is pushed out and lies flat on the water. The stabilization process boils down to the fact that the UV radicals lying on the surface of the particle protect it from sticking to another similar particle stabilized by a surfactant. Usually, a stabilizer is introduced to achieve a better degree of dispersion (grinding) of the system.
The use of stearic acid
Stearic acid is an intermediate component for the production of:
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soaps
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fats
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rubber vulcanization activators
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epoxy resins for surface coatings
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of synthetic rubbers
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emulsifiers (stabilizers) polymerization
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cosmetic formulations
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pharmaceutical creams
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candles
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lubricants in pharmaceuticals
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anti-adhesives in bakery and confectionery products
Stearic acid in the production of lubricants and softening materials
Sodium and lithium stearates have good lubricity due to their soft consistency. Moreover stearate salts of zinc, calcium, cadmium and lead with the general formula C17H35COOR, where R = Zn, Ca, Cd, Pb, are used for plasticization of PVC and its processing, in the production of automobile tires as a dispersing agent, which contributes to better grinding and uniform particle distribution. Stearic acid is used together with castor oil to prepare softeners (plasticizers) when sizing textiles.
Stearic acid in the production of cosmetics and detergents
Stearic acid is obtained from animal fat. The substance is used to produce:
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detergents
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soaps
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cosmetics
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personal care items:
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shampoos
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creams
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shaving foam
Soap is not made directly from stearic acid, but it is an integral component of its production. Soap is obtained by saponification of triglycerides, esters of stearic acid. Molten esters of stearic acid with ethylene glycol, stearate and glycol distearate are used to create a pearlescent effect in shampoos, soaps and other cosmetic products. Detergents are obtained from amides and quaternary alkylammonium derivatives of stearic acid.
Production of niche products from stearic acid
Stearic acid finds application in candle production, is used together with sugar or corn syrup as a hardener in sweets, for the production of food additives being inexpensive and chemically harmless.
In fireworks, the substance is often used to coat metal powders such as aluminum and iron. This prevents their oxidation, allowing the fireworks to be stored for a longer period of time.
A mixture of stearic, palmitic and oleic acids is called stearin and is used to produce candles, paper, rubber and textiles.
Stearic acid in PVC processing
Stearic acid and its compounds in the production and processing of polymers perform the following functions:
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Thermostabilization
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An integral component of greases
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Internal and external lubrication in the processing of PVC and polypropylene
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Plasticizer for plastic processing
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A hydrophobizer that provides water-repellent properties
Thermal stability is an important characteristic of PVC, which determines the destruction (destruction) of the product made from it under the influence of high temperatures. Thermal degradation affects the physical and mechanical properties of PVC and limits the cyclical nature of its use — the possibility of recycling pipes and other PVC products. For this reason, PVC recycling companies use heat stabilizers that prevent the penetration of labile chlorine, replacing them with solid functional groups that can resist its cleavage. Stearic acid is used as an external lubricant for processing rigid PVC.
Metal stearate molecules can also act as stabilizers. For example, calcium stearate acts as an internal lubricant in PVC processing, reducing friction between polymer grains. Calcium stearate is a thermally stable component of the formulation, it has a high softening temperature and does not become greasy when exposed to high temperatures, meeting the necessary criteria. Calcium stearate is also used as a separating (dispersing) agent and hydrochloric acid absorber in PVC processing.