Comparison Table of the Performance of different Amino Acid Based Surfactants

Basic Concepts of Amino Acid-Based Surfactants

Amino acid surfactants are a group of surfactants that use amino acids or amino acid derivatives as their structural element. Amino acids, the protein's building blocks, are hydrophilic and hydrophobic, which make them perfect candidates for surfactants. Such surfactants are often produced by reacting amino acids with fatty acids, alcohols or other hydrophobic molecules to create amphiphilic molecules.

The main feature of amino acid surfactants is their biodegradability. But, unlike traditional petroleum-based surfactants, amino acid surfactants disperse naturally into harmless byproducts that help minimize environmental contamination. Additionally, amino acids are naturally occurring, non-toxic, and coming from renewable resources, which makes these surfactants a sustainable and green option. Comparing to conventional surfactants (anionic/nonionic surfactants), amino acids provide superior safety and environmental performance.

Performance Characteristics of Amino Acid-Based Surfactants

Amino acid surfactants have some major performance properties, which make them useful for applications everywhere:

Surface Activity

Amino acid surfactants are particularly good at lowering surface tension, which is critical for emulsification, foaming and cleaning. They also have lower critical micelle concentration (CMC) so they work well at low concentrations.

Biodegradability

Biodegradability is one of the main features of amino acid surfactants. Because they're naturally derived, these surfactants dissociate into inert molecules with low environmental footprints and therefore are safe in aquatic environments.

Low Toxicity and Safety

Amino acid surfactants are not toxic, and are safe for personal care, medicine, and food. They are generally preferable to older surfactants, which can irritate or destroy humans and the environment.

Compatibility

These surfactants are very compatible with other ingredients in formulations, including personal care and cleaning products. Their robustness and pliability in many conditions makes them suitable for a variety of uses.

Composition of Amino Acid-Based Surfactants

Surfactants containing amino acids and hydrophobic chains. Their molecular structure is usually made up of polar hydrophilic bonds and nonpolar hydrophobic chains. Below is an overview of their typical composition and main characteristics:

Basic Composition of Amino Acid-Based Surfactants

1. Hydrophilic Group

Provided by amino acids, typically including the following structures:

• Amino Group (-NH₂): Contributes hydrophilicity and facilitates hydrogen bonding with water molecules.
• Carboxyl Group (-COOH): Extremely polar, increases water affinity.
• Side Chain Functional Groups: Like hydroxyl (-OH), carboxyl (-COOH), amino (-NH₂) or aromatic rings, also to manage hydrophilicity and solubility.

The structural diversity of amino acids allows for the design of surfactants with varying hydrophilic properties.

2. Hydrophobic Chain

Supplied by long-chain fatty acids or fatty alcohols:

• Saturated Fatty Chains: For example lauric acid (C12) and stearic acid(C18) which provides stable hydrophobicity.
• Unsaturated Fatty Chains: (Like oleic acid, C18:1) gives the texture elasticity and lowers surface tension.

Longness of the fatty chain plays an important role in hydrophobicity and CMC.

3. Linkage Group

Connects the amino acid to the hydrophobic chain through specific chemical bonds, primarily including:

• Ester Bond (-COO-): Commonly formed from reactions between amino acids and fatty alcohols, easily degradable and environmentally friendly.
• Amide Bond (-CONH-): Produced from reactions between amino acids and fatty acids or acyl chlorides, offering higher stability.
• Ether Bond (-O-): Less common, typically used in surfactant designs for specific applications.

Examples of Typical Amino Acid-Based Surfactant Compositions

• Glycine-based surfactants: Featuring -NH₂ and -COOH functional groups, combined with fatty acids like lauric acid.
• Glutamic acid-based surfactants: Containing two carboxyl groups, offering enhanced hydrophilicity and compatibility with diverse applications.
• Lysine-based surfactants: With a second amino side group that adds a specific feature, like antimicrobial.

Combining amino acids and fatty chains, amino acid surfactants can be configured for any property and any application, and are highly polyvalent and sustainable.

Table 1. Composition of Amino Acid-Based Surfactants

Design Features and Flexibility

1. Amino Acid Diversity:

These amino acids (e.g., glutamic acid, glycine, lysine) confer special properties to surfactants like water solubility, foaming and biodegradability.

2. Fatty Chain Modulation:

The length and saturation of the fatty chain determine hydrophobicity and functional applications, allowing optimization for specific needs.

3. Environmental Friendliness:

Since amino acids and fatty acids are natural compounds, amino acid surfactants are highly biodegradable and toxic – in accordance with green chemistry.

Surfactants with amino acids are a hydrophilic amino acid unit and a hydrophobic fatty chain unit bonded together chemically to linkage groups. They are also a versatile class of green surfactants with very high performance.

Amino Acid-Based Surfactants vs. Other Surfactants

The most eco-friendly, efficient and toxicity-low surfactants among all surfactants are amino acid surfactants. Below you can see the complete comparison to other popular surfactants like petroleum-based, sugar-based, and protein-based surfactants.

Table 2. Comparison of Amino Acid-Based Surfactants vs. Other Surfactants

Comparative Analysis

1. Environmental Friendliness:

Organic surfactants like amino acids are more eco-friendly and biodegradable than petroleum surfactants.

They have better manufacturing flexibility and raw material sources than sugar and protein surfactants.

2. Performance and Application Scope:

Amino acid-based surfactants have comparable performance to petroleum-based surfactants but are better suited for mild applications (e.g., personal care products).

They demonstrate higher compatibility and stability across diverse applications compared to sugar-based and protein-based surfactants.

3. Economics and Market Potential:

Amino acid surfactants are getting cheaper, and demand for them is rising as green chemistry becomes more prevalent and as consumers become more environmentally aware.

Oil-based surfactants dominate because they are cheap and mature, but their market share can shrink with environmental legislation.

Performance Comparison of Different Amino Acid-Based Surfactants

Performance of amino acid surfactants differ greatly depending on amino acid sequences, chain lengths and substituent compositions. Below is a comparative analysis of the performance of several common amino acid-based surfactants.

Table 3. Comparison of Foaming Performance Across Different Amino Acids with the Same Salt

Conclusion

Glycine salt-based and alanine salt-based surfactants generally exhibit superior foaming performance, with high foam height and good stability.

Glutamate salt-based surfactants have good foam stability and moderate generation rate, but the foam height is relatively low.

Aspartate salt-based surfactants show poor foaming performance, with slow foam generation and low stability, requiring optimization for specific applications.

Table 4. Comparison of Foaming Performance Across Different Fatty Acids with the Same Amino Acid

Conclusion

Glycine-laurate salt and glycine-palmitate salt both feature high foam height and stability for use where durable foam is needed.

Glycine-stearate salt has an equal foam quality that sits somewhere between foam stability and foam generation.

Glycine-oleate salt has poor foam stability, and the generated foam tends to collapse, necessitating improvement for better performance.

Glycine-myristate salt maintains good foam stability at high concentrations, making it suitable for applications requiring rapid foam generation.

Table 5. Comparison of Foaming Performance Across Different Salts with the Same Amino Acid

Conclusion

Glycine-sodium chloride and glycine-ammonium chloride are both good foam height, stability, and genrate, which is great for uses where fast and durable foam is required.

Glycine-sodium sulfate and glycine-potassium chloride have relatively good performances that would be acceptable for most use cases.

Glycine-sodium acetate quickly foams but it's unstable, so in many uses it's not practical.

Table 6. Comparison of Foaming Performance Using Different Manufacturing Processes

Conclusion

The esterification and solvent methods for glycine-sodium chloride surfactants exhibit higher foam height and stability, making them suitable for applications requiring rapid foam formation and prolonged stability.

The amination method shows moderate foam height and good stability, ideal for balanced foam formation and stability.

Temperature control and mild condition methods, while less stable than other processes, may offer better stability at specific concentrations, especially under mild operating conditions.

Table 7. Comparison of Surfactants with Different Preservatives

Conclusion

Glycine-sodium chloride with benzoic acid demonstrates high foam height and stability, suitable for applications requiring rapid and stable foam formation.

p-Hydroxybenzoic acid-based surfactants offer good stability for balanced foam generation and stability.

Ethyl p-hydroxybenzoate produces fast foam but with lower stability, which may be less suitable for certain applications.

Methylisothiazolinone-based surfactants show good stability and foam formation rates but may be sensitive to concentration changes.

Formaldehyde-based surfactants exhibit lower stability at higher concentrations but perform well at low concentrations, fitting specific niche applications.

Table 8. Solubility Comparison of Amino Acid-Based Surfactants

Conclusion

Surfactants derived from polar amino acids (e.g., glutamic acid, lysine) have excellent water solubility, making them ideal for water-based personal care products and detergents.

Surfactants derived from non-polar or hydrophobic amino acids (e.g., leucine, isoleucine) exhibit better solubility in organic solvents, suitable for solvent-based coatings and oil-based cleaners.

The polarity of amino acid side chains and the length of the fatty chain are key parameters influencing solubility. Optimizing these structures can help design surfactants tailored to various solvent requirements.

Reference

1. Bordes, R., et al. "Amino acid-based surfactants–do they deserve more attention?." Advances in Colloid and Interface Science 222 (2015): 79-91.