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Basics of the HLB System

by | Nov 10, 2015

The HLB System: Basic Nonionic Surfactant Evaluation

Creating new formulations to meet today’s cleaning and regulatory challenges requires careful selection of surfactant ingredients.

Given the breadth of surfactants available in today’s specialty chemical market, formulators need efficient tools to narrow down their choices.

One of the most practical and effective tools is the HLB system.

The HLB system provides a framework for predicting how surfactants will behave in emulsion systems.

This article provides a basic overview of the HLB system and how it can be used to optimize formulations with nonionic surfactants.

What is the HLB System (and why does it matter)?

Surfactant molecules have both hydrophilic (water loving) and lipophilic (oil loving) groups. The HLB system, which stands for “Hydrophilic Lipophilic Balance”, indicates how the proportion of those groups will affect surfactant behavior in emulsions.

HLB numbers correspond to the degree of water or oil solubility of a particular surfactant.

Lower HLB numbers indicate better oil (non-polar) solubility. Higher HLB numbers indicate better water (polar) solubility.

Surfactants with low HLB values are more suited for water-in-oil emulsions (W/O), and higher HLB values are better for oil-in-water emulsions (O/W).

HLB Numbers By Application

Surfactant HLB values are proportional to the polarity of the hydrophilic head group.

For example, with alcohol ethoxylates, the HLB value is directly proportional to the surfactant’s ethylene oxide (EO) chain length.

More specifically, a linear alcohol ethoxylate with 8 moles EO will have a higher HLB value, and better water solubility, than a linear alcohol ethoxylate with 3 moles EO.

Calculating HLB values of Nonionic Surfactants

William C. Griffin of the Atlas Paper Company introduced the HLB system in 1949.

Understanding the importance of these hydrophilic-lipophilic proportions, Griffin devised a method to calculate HLB values of nonionic surfactants within a range of 1 – 20.

The HLB method is based on the premise that “all surfactants combine hydrophilic and lipophilic groups in one molecule and that the proportion between the weight percentages of these two groups for nonionic surfactants is an indication of the behavior that may be expected from that product.”

 

Calculation of HLB Values of Nonionic Surfactants¸ William C. Griffin, Atlas Powder Company, New York City, May 14, 1954.

Using the Griffin method, an HLB value is equal to the molecular weight percent of the hydrophilic portion divided by 5.

With our linear alcohol ethoxylate example, the hydrophilic portion of the surfactant is the ethylene oxide (EO) chain.

Our data sheet indicates that EO content is 69.7%. Therefore, the HLB value of this molecule would be 13.9 (69.7/5).

How is the HLB system used?

The HLB system is used by formulators to narrow down potential surfactant candidates for use in an emulsion system.

In our case, this often involves selecting nonionic surfactants to incorporate into oil-in-water systems.

Just as nonionic surfactants have HLB values, oils have HLB requirements.

HLB Requirements for Oils

A formulator will begin the surfactant selection process by matching surfactant HLB values with the HLB requirement of the oil(s)* to be emulsified.

Blended HLB Values

Because oil HLB requirements do not always directly correspond to nonionic surfactant HLB values, it is usually most effective to blend surfactants with high and low HLB values at varying ratios.

Blending enables formulators to target different HLB requirements and provide a wider range of solubility for cleaning and degreasing performance.

The HLB value of a surfactant blend is the weighted average of HLBs of the individual surfactants.

For example, to target a petroleum-based oil with an HLB requirement of 10, a formulator may choose a 50/50 blend of two surfactants: Surfactant A with an HLB of 12 and Surfactant B with a lower HLB of 8.

In this example, the blended HLB value would be 10.

Of course, this is a very simplified example, but the blending of surfactants is often critical to finding an effective and efficient surfactant component for formulated solutions.

The ultimate goal is to find the optimal ratio of surfactants to achieve performance goals and maintain emulsion stability, rheology and other desired characteristics, while controlling raw material costs.

Optimized Surfactants

In addition to testing different ratios of high and low HLB components in a solution, formulators can test surfactants with broader solubility characteristics to make the task more efficient.

For example, many surfactants are available with mid-range HLB values (i.e. approximately 11) for a wider range oil solubility.

Semi-formulated concentrates, containing multiple surfactant components, can often accommodate the full spectrum of HLB ranges from 0 – 20.

Conclusion

The HLB provides a rough guide to choosing optimal surfactants for an emulsion system.

Building emulsion systems can be accomplished with varying ratios of low and high HLB surfactants, mid-range HLB surfactants, or multi-component concentrates for formulating and cleaning efficiency.

* Like blended HLB values of surfactants, the HLB requirement of multiple oil components is the weighted average of the HLB requirements of the individual oil components (i.e. HLB requirement for 50/50 blend of petroleum [10] and fatty acid [14] would be 12)

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