In modern industries, surfactants are indispensable components. They appear in coatings, cosmetics, food, pharmaceuticals, and many other dispersion systems. To choose the right type, the HLB index is always the leading criterion. It is a key measure that reflects the balance between the hydrophilic and lipophilic parts of the molecule.
WHAT IS HLB?
HLB stands for Hydrophilic-Lipophilic Balance. It refers to the balance between water-loving and oil-loving parts. The index usually ranges from 0 to 20. Lower numbers indicate a stronger lipophilic nature, while higher values show stronger hydrophilic behavior.
In every surfactant molecule, there are two ends: one hydrophilic and one lipophilic. The balance between these ends defines the property and usage of the surfactant. By using HLB, one can predict if a surfactant is suitable for O/W or W/O emulsions, for dispersing pigments, or for defoaming purposes.
THE MEANING OF HLB INDEX
HLB is not just a theoretical number. It carries clear and practical value. Surfactants with HLB from 1 to 3 are suitable for antifoaming agents. Those with HLB from 3 to 6 are used for water-in-oil emulsions. Surfactants around 7 to 9 help disperse pigments and stabilize solid particles.
When HLB is in the range of 8 to 12, the surfactant acts as a wetting agent and improves adhesion. Values from 10 to 15 are suitable for oil-in-water emulsions, which are common in waterborne coatings. If HLB is above 15, the surfactant is strongly hydrophilic, widely used in detergents and foaming agents.
PRACTICAL APPLICATIONS
Emulsification
In the coatings industry, emulsification is a crucial step. Waterborne paints require surfactants with HLB from 10 to 15 to disperse resins into water. If the index is chosen wrongly, the emulsion will be unstable and prone to separation. Choosing the right HLB ensures both durability and appearance of the coating. In cosmetics and food, the same principle applies to creams or stable emulsified sauces.
Pigment dispersion
Pigments and colorants are often difficult to disperse in liquid phases. Surfactants with HLB between 6 and 9 stabilize pigments, prevent sedimentation, and reduce paint viscosity. As a result, coatings show high coverage and uniform color. With better stability of dispersion, HLB also helps save raw materials and extend product lifetime. This creates clear economic benefits in large-scale paint production.
Wetting
In many applications, adhesion to metal, wood, or plastic substrates is critical. Surfactants with HLB values of 8 to 12 reduce surface tension and improve spreading. This leads to smooth coatings with fewer defects. In printing and plastics, proper HLB surfactants also enhance adhesion and improve the quality of the final products.
Foam control
During mixing or spraying, foam is often generated and can damage coating quality. Surfactants with very low HLB values, from 1 to 3, act as defoamers and stabilize the process. Controlling foam ensures a smoother film and prevents surface defects. In industries such as paper or food, antifoaming surfactants are equally essential to maintain efficiency.
HOW TO CALCULATE HLB
The HLB index can be calculated from the molecular structure of the surfactant. The general formula is:
HLB = 20 × (Mh / M)
Where Mh is the molecular mass of the hydrophilic part, and M is the total molecular mass. This formula helps predict the value from chemical structure. However, in practice, manufacturers usually provide HLB data, making it easier for users to apply accurately
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