Cocamidopropyl Betaine (CAPB) - Mild Amphoteric Surfactant / Articles

Cocamidopropyl Betaine (CAPB) - Properties, Applications, and Safety

Cocamidopropyl betaine (CAPB, CAS 61789-40-0) is a mild, amphoteric surfactant derived from coconut oil and dimethylaminopropylamine. It is widely used in personal care, household cleaning, and industrial formulations as a secondary surfactant, foam booster, viscosity builder, and conditioning agent. Its amphoteric nature – possessing both positive and negative charges depending on pH – enables compatibility with anionic, cationic, nonionic, and other amphoteric surfactants. This versatility, combined with excellent mildness and biodegradability, makes CAPB a preferred ingredient in formulations for sensitive skin, baby care, and eco-friendly products.

Chemical Structure and Properties

CAPB is an organic compound with the molecular formula C₁₉H₃₈N₂O₃ and a molecular weight of approximately 342.5 g/mol. Its structure can be represented as RCONH(CH₂)₃N⁺(CH₃)₂CH₂COO⁻, where R is the fatty acid chain derived from coconut oil. The compound is typically supplied as a pale yellow to clear liquid with an active content of 30–35% solids. Key physical properties include:

Appearance: Clear to pale yellow liquid
pH (1–5% aqueous solution): 4.5–7.0 (depending on grade and dilution)
Viscosity: Approximately 30 cPs at 25°C
Specific gravity: ~1.04 at 25°C
Pour point: ~ –5°C
Flash point: ≥150°C
Cloud point: ≤5°C

CAPB remains stable across a wide pH range (typically 4–9) and exhibits excellent lime-soap dispersing properties, making it effective even in natural soap formulations.

Mechanism of Action

As an amphoteric surfactant, CAPB can function as either a cationic or anionic surfactant depending on the pH of the solution. At acidic pH, it carries a positive charge, while at alkaline pH it carries a negative charge. This dual nature enables it to interact with a wide range of other surfactants and ingredients, dissolving oils and dirt while remaining mild to skin and eyes. CAPB reduces surface tension, enhances foaming, stabilizes foam structure, and contributes to viscosity building in finished formulations.

Applications

Personal Care and Cosmetics: CAPB is widely used in shampoos, body washes, facial cleansers, liquid hand soaps, baby care products, bubble baths, and shaving foams. It functions as a foam booster, viscosity builder, conditioning agent, and mild cleanser. It is also used in hair conditioners and cream rinses. Its gentle nature makes it particularly suitable for sensitive skin and baby care formulations.

Household and Industrial Cleaning: CAPB is used in dishwashing liquids, bathroom cleaners, hard surface cleaners, and institutional cleaning products as a foam stabilizer and mild surfactant.

Pet Care: Shampoos for pets often contain CAPB due to its mildness and effective cleansing.

Other Applications: CAPB is also used as an antistatic agent, emulsifier, and viscosity modifier in various industrial and agrochemical formulations.

Safety and Toxicology

The Cosmetic Ingredient Review (CIR) Expert Panel has evaluated the safety of cocamidopropyl betaine and related amidopropyl betaines. The Panel concluded that these ingredients are safe for use in cosmetics, provided they are formulated to be non-sensitizing. Specifically:

Rinse-off products: CAPB is safe for use in rinse-off cosmetic products at current levels of use.
Leave-on products: The concentration of use for products designed to remain on the skin for prolonged periods should not exceed 3.0% (expressed as a 10% dilution of a full-strength CAPB solution with 30% activity).
Skin and eye irritation: CAPB is considered a mild, non-irritating surfactant at typical use concentrations. It is widely used in baby care and sensitive skin formulations.
Sensitization: When formulated to be non-sensitizing, CAPB does not present significant sensitization risks.
Environmental profile: CAPB is readily biodegradable. In an OECD 301E test, biodegradation exceeded 60% within 28 days, meeting the 10‑day window criterion. It is considered to have very low persistence in the environment.

Storage and Handling

CAPB should be stored in tightly sealed containers at 5–30°C, protected from moisture and direct sunlight. Stainless steel, polyethylene, or glass-lined equipment is recommended for storage to prevent corrosion and contamination. The material may separate on standing or at low temperatures and may require agitation and warming prior to use. Use appropriate personal protective equipment (gloves, safety goggles) when handling concentrated solutions. The shelf life is typically 24 months under recommended storage conditions.

Conclusion

Cocamidopropyl betaine (CAPB) is a mild, versatile, and environmentally friendly amphoteric surfactant derived from renewable coconut oil. Its excellent foam-boosting, viscosity-building, and conditioning properties, combined with its compatibility with other surfactants and favorable safety profile, make it a key ingredient in personal care, household cleaning, and industrial formulations. As consumer demand for gentle, sustainable, and effective products continues to grow, CAPB remains a preferred choice for formulators seeking both performance and safety.