Sodium Stearate, Sodium Octadecanoate, Sodium Soap, 822-16-2

SODIUM STEARATE

Sodium Stearate / Sodium Octadecanoate / Sodium Soap
CAS Number: 822-16-2
EC Number: 212-490-5

1. PRODUCT IDENTIFICATION AND CHEMICAL IDENTITY

Sodium stearate is the sodium salt of stearic acid (octadecanoic acid). It is a white, odorless powder, flake, or granule classified as a metal salt (fatty acid salt) and is commonly known as a "sodium soap." As one of the most common soap compounds, sodium stearate is a key ingredient in traditional bar soaps and a versatile surfactant. It is produced by the saponification of stearic acid with sodium hydroxide or by the neutralization of stearic acid with sodium carbonate. Sodium stearate is highly soluble in water and exhibits excellent emulsifying, stabilizing, and thickening properties. Its versatility and mildness make it widely used in soaps, detergents, cosmetics, pharmaceuticals, food processing, plastics, rubber, and many other industrial applications. Sodium stearate is a white powder or flake that is odorless and has a slightly soapy, bitter taste.

2. PHYSICAL AND CHEMICAL PROPERTIES

Sodium stearate is a white, odorless powder, flake, or granule with a slightly soapy, bitter taste. Its true density is approximately 1.02-1.05 g/cm³, while its bulk density ranges from 0.2-0.5 g/cm³ depending on the form. The melting point is approximately 245°C, at which decomposition begins. At 25°C, it is soluble in water (150-200 g/L), slightly soluble in alcohol, and insoluble in hydrocarbons and oils. The pH of a 1% aqueous solution is approximately 10-11, indicating basic character. As an amphiphilic compound, it has a hydrophilic head and a hydrophobic tail, giving it surfactant properties. Heavy metals are typically ≤ 20 ppm (as Pb). Free fatty acid content is ≤ 0.5%, loss on drying is ≤ 2.0%, and sodium oxide (Na₂O) content is approximately 10-12%. It is stable under normal conditions but sensitive to light. It is incompatible with strong acids, strong oxidizing agents, and hard water ions (Ca²⁺, Mg²⁺), which can form insoluble calcium and magnesium stearates.

3. CHEMICAL PROPERTIES AND REACTIONS

Sodium stearate is a sodium metal salt and a fatty acid soap (sodium soap). Its chemical behavior is determined by the properties of the stearate anion and the sodium cation.

Reaction with Acids:

Sodium stearate reacts with strong acids to form stearic acid and the corresponding sodium salt:

C₁₇H₃₅COONa + HCl → C₁₇H₃₅COOH + NaCl

Reaction with Hard Water Ions:

Sodium stearate reacts with calcium and magnesium ions in hard water to form insoluble calcium and magnesium stearates (soap scum):

2 C₁₇H₃₅COONa + Ca²⁺ → (C₁₇H₃₅COO)₂Ca↓ + 2 Na⁺

2 C₁₇H₃₅COONa + Mg²⁺ → (C₁₇H₃₅COO)₂Mg↓ + 2 Na⁺

Hydrolysis:

As a salt of a weak acid (stearic acid) and a strong base (sodium hydroxide), sodium stearate undergoes hydrolysis in water to form a basic solution:

C₁₇H₃₅COONa + H₂O ⇌ C₁₇H₃₅COOH + NaOH

Saponification:

Sodium stearate is itself a product of saponification (fat + NaOH → glycerol + sodium stearate).

Thermal Decomposition:

At temperatures above 245°C, sodium stearate decomposes to form sodium carbonate, carbon dioxide, and hydrocarbons.

Surfactant Properties:

As a surfactant, sodium stearate reduces surface tension and interfacial tension, enabling emulsification, wetting, and foaming.

Micelle Formation:

In aqueous solution above the critical micelle concentration (CMC), sodium stearate forms micelles, which are spherical aggregates of surfactant molecules with the hydrophobic tails inward and the hydrophilic heads outward.

4. PRODUCTION METHODS

Sodium stearate is produced industrially primarily by the saponification of stearic acid with sodium hydroxide or by the neutralization of stearic acid with sodium carbonate.

Detailed Production Process (Saponification - Most Common):

1. Raw Material Preparation: Stearic acid (typically > 95% purity) and sodium hydroxide (caustic soda) are prepared. Stearic acid is typically melted.

2. Reaction: Melted stearic acid is added to a solution of sodium hydroxide in water at 80-100°C with stirring:

C₁₇H₃₅COOH + NaOH → C₁₇H₃₅COONa + H₂O

3. Cooling: The resulting sodium stearate solution is cooled to solidify the product.

4. Drying: The solid sodium stearate is dried to reduce moisture content to ≤ 2.0%.

5. Milling and Sieving: The dried product is milled to the desired particle size (powder, flake, or granule) and sieved.

6. Packaging: The final product is packaged in 25 kg bags, drums, or FIBCs.

Reaction Equation (Saponification with Sodium Hydroxide):

C₁₇H₃₅COOH + NaOH → C₁₇H₃₅COONa + H₂O

Reaction Equation (Neutralization with Sodium Carbonate):

2 C₁₇H₃₅COOH + Na₂CO₃ → 2 C₁₇H₃₅COONa + CO₂ + H₂O

5. COMPARISON WITH OTHER METAL STEARATES

Sodium stearate is highly soluble in water and has excellent foaming properties, making it ideal for bar soaps and other cleansing products. Potassium stearate is also water-soluble and used in liquid soaps. Calcium stearate and magnesium stearate are insoluble in water and are primarily used as release agents, lubricants, and stabilizers in plastics, rubber, and pharmaceutical applications.

6. APPLICATIONS AND INDUSTRIAL USES

Sodium stearate is a versatile compound with a wide range of applications across various industries due to its excellent emulsifying, stabilizing, thickening, and surfactant properties.

6.1. Soaps and Detergents (Most Important Application)

Sodium stearate is one of the most common soap compounds and is the primary ingredient in traditional bar soaps. It provides excellent cleansing, foaming, and lathering properties. In soaps, sodium stearate is produced by the saponification of fats and oils (triglycerides) with sodium hydroxide. It is also used in synthetic detergent bars (syndet bars) as a binder and structurant. In laundry detergents, dishwashing detergents, and industrial cleaners, sodium stearate functions as a surfactant and builder, helping to remove dirt and grease.

6.2. Cosmetics and Personal Care Products

Sodium stearate is widely used in cosmetics and personal care products as an emulsifier, stabilizer, thickener, binder, and consistency agent. It is found in creams, lotions, makeup products, deodorants, shampoos, conditioners, sunscreens, toothpaste, and shaving creams.

6.3. Food Industry

Sodium stearate is used as a food additive (E 470a) as an emulsifier, stabilizer, and anti-caking agent. It is used in baked goods as a dough conditioner and emulsifier, in confectionery products, in margarine and spreads, and in ice cream as a stabilizer and emulsifier.

6.4. Pharmaceutical Industry

Sodium stearate is used in the pharmaceutical industry as a binder, lubricant, emulsifier, and stabilizer, although it is not as common as magnesium stearate.

6.5. Plastics and Rubber Industry

Sodium stearate is used in the plastics and rubber industry as a release agent, lubricant, stabilizer, anti-blocking agent, dispersing agent, and antistatic agent. It is used in the processing of PVC, polyethylene, polypropylene, and other polymers.

6.6. Paper Industry

Sodium stearate is used in the paper industry as a coating agent, sizing agent, and release agent.

6.7. Textile Industry

Sodium stearate is used in the textile industry as a softener, lubricant, antistatic agent, and emulsifier.

6.8. Other Applications

7. SAFETY AND HEALTH INFORMATION

Sodium stearate is generally considered to have low toxicity and is widely used in food, cosmetics, and pharmaceutical applications.

7.1. Toxicological Data

7.2. Health Effects

8. FIRST AID MEASURES

9. SAFETY INFORMATION (GHS CLASSIFICATION)

Sodium stearate is not classified as a hazardous substance under GHS. However, fine powder may cause respiratory irritation.

Signal Word: WARNING

Hazard Statements (H-Codes):

Precautionary Statements (P-Codes):

10. FIREFIGHTING MEASURES

11. ACCIDENTAL RELEASE MEASURES

12. STORAGE AND HANDLING

Sodium stearate should be stored in cool, dry, well-ventilated areas in tightly closed original containers. It is slightly hygroscopic and should be protected from moisture. It should be protected from light and heat. Contact with strong acids and strong oxidizing agents should be avoided. Proper grounding should be used to prevent static electricity accumulation.

Handling Notes:

• Avoid dust generation (use enclosed systems, local exhaust ventilation)

• Avoid contact with skin and eyes (use protective gloves and goggles)

• Avoid breathing dust (use dust mask or respirator)

• Keep away from ignition sources

• Do not allow material to become wet (may cake and become difficult to handle)

13. TRANSPORT INFORMATION

Sodium stearate is not classified as a dangerous good for transport. It is shipped in 25 kg bags, drums, or FIBCs. During transport, protect from moisture, impact, and excessive heat.

14. REGULATORY INFORMATION

Regulatory Status:

15. OTHER NAMES AND DATABASE IDENTIFIERS

Database Identifiers:

16. ENVIRONMENTAL INFORMATION

17. APPLICATION SUMMARY TABLE

18. PHYSICAL FORMS

19. COMPARISON WITH OTHER SODIUM SOAPS

Sodium stearate is the primary component in traditional hard bar soaps. Sodium palmitate is also a common component in bar soaps, while sodium oleate is more common in liquid soaps and soft soaps.

20. SUMMARY AND CRITICAL WARNINGS

SUMMARY:

Sodium stearate (C₁₈H₃₅NaO₂, CAS 822-16-2) is the sodium salt of stearic acid (octadecanoic acid). It is a white, odorless powder, flake, or granule classified as a metal salt (fatty acid salt) and is commonly known as a "sodium soap." The molecular weight is 306.47 g/mol, and the melting point is approximately 245°C. It is soluble in water (150-200 g/L at 25°C), slightly soluble in alcohol, and insoluble in hydrocarbons and oils. It is produced by the saponification of stearic acid with sodium hydroxide or by neutralization with sodium carbonate. As one of the most common soap compounds, sodium stearate is a key ingredient in traditional bar soaps and a versatile surfactant. It is widely used in soaps and detergents, cosmetics, food processing, pharmaceuticals, plastics, rubber, paper, and textiles. It has low toxicity and is not classified as a hazardous substance under GHS. It is stored in cool, dry, well-ventilated areas, protected from light, heat, and moisture. Packaging: 25 kg bags, drums, or FIBCs.

Key Properties:

Major Application Areas:

Key Safety Points:

• LOW TOXICITY: GRAS by FDA; approved as food additive

• SLIGHTLY HYGROSCOPIC: Protect from moisture; store in tightly closed containers

• MILD IRRITANT: May cause mild skin and eye irritation

• RESPIRATORY IRRITANT: May cause respiratory irritation from dust at high concentrations

• STORAGE: Store in cool, dry, well-ventilated area, protected from light, heat, and moisture

• PPE REQUIRED: Dust mask, safety goggles, protective gloves (for handling powder)

• FOOD ADDITIVE: Approved as E 470a for use in food products

• REACTION WITH HARD WATER: Reacts with calcium and magnesium ions to form insoluble soap scum

CRITICAL WARNINGS:

Soap and Detergent Application: Sodium stearate is one of the most common soap compounds and is the primary ingredient in traditional bar soaps. It provides excellent cleansing, foaming, and lathering properties. In soaps, sodium stearate is produced by the saponification of fats and oils with sodium hydroxide. It is also used in synthetic detergent bars as a binder and structurant.

Surfactant Properties: As a surfactant, sodium stearate reduces surface tension and interfacial tension, enabling emulsification, wetting, and foaming. This makes it valuable in a wide range of cleaning, personal care, and industrial applications. In aqueous solution, sodium stearate forms micelles, which are spherical aggregates of surfactant molecules that help solubilize oils and dirt.

Food Additive: Sodium stearate is approved as a food additive (E 470a) as an emulsifier, stabilizer, and anti-caking agent. It is used in baked goods, confectionery, margarine, spreads, and ice cream. The FDA has approved it as Generally Recognized as Safe (GRAS).

Reaction with Hard Water: One of the limitations of sodium stearate is its reaction with calcium and magnesium ions in hard water to form insoluble calcium and magnesium stearates (soap scum). This reduces its cleansing efficiency and can leave residues on surfaces. This is why synthetic detergents (syndets) were developed as alternatives to traditional soaps.

Cosmetic Use: Sodium stearate is widely used in cosmetic products as an emulsifier, stabilizer, thickener, and binder. It is found in creams, lotions, makeup products, deodorants, shampoos, conditioners, and toothpaste. Its mildness and compatibility with skin make it suitable for personal care applications.

Plastic and Rubber Use: In plastics and rubber, sodium stearate is used as a release agent, lubricant, stabilizer, anti-blocking agent, and dispersing agent. It is used in the processing of PVC, polyethylene, polypropylene, and other polymers. It improves flow properties, prevents sticking, and stabilizes the polymer against heat degradation.

Environment: Sodium stearate is readily biodegradable due to its fatty acid component. It has low toxicity to aquatic organisms. However, large discharges to water bodies can cause foam formation and oxygen depletion due to biodegradation. Proper waste management practices should be followed.

Important Disclaimer: This Technical Data Sheet (TDS) is for informational purposes only. The information provided is based on available data and is believed to be accurate. However, the user is solely responsible for determining the suitability of the product for their specific application and for complying with all applicable regulations and safety requirements. For complete safety, handling, storage, and regulatory compliance information, always refer to the official Safety Data Sheet (SDS/MSDS) provided by the manufacturer/supplier. Users are responsible for testing the product in their own processes and applications. All local, national, and international regulations must be followed when working with sodium stearate.