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Tuesday, December 22, 2009

The Hydrophile-Lipophile Balance (HLB Scale)

1. Surfactant possess both hydrophilic and lipophilic portions, so there must be some scale to measure the balance between these two opposing tendencies.

2. Griffin (1949) developed an arbitrary scale to serve as a measure of hydrophilic-lipophilic balance (HLB) of surface active agents.

3. This HLB scale is numerical scale extending from 1 to 20.

4. The more hydrophilic surfactants have a high HLB number > 10, while surfactants with an HLB < 10 are considered to be lipophilic.

5. The HLB value helps in the selection of a proper surfactant for a particular application.

6. The HLB of a number of polyhydric alcohols and fatty acid esters such as glyceryl monostearate, can be calculated by using the formula:

HLB = 20(1 - S/A)

where S is the saponification number of the ester and A is the acid number of the fatty acid.

7. But the saponification number for many substances like bees-wax and wool-fat derivatives cannot be easily estimated.

8. In such cases, the following relation is used,

HLB = (E + P)/5

where E is the percent by weight of oxythelene chains and P is the percent by weight of polyhydric alcohol groups in the molecules.

9. obviously, when the molecule consist only of oxyethylene groups, equation becomes

HLB = E/5

10. Davies calculated the HLB values for surface active agents by splitting the various surfactant molecules into their component groups, to each of which is assigned a group number.

11. The summation of the respective group number permits the calculation of the HLB value according to the equation

HLB = ∑ (hydrophilic group numbers) - (lipophilic group numbers) + 7

1 comment:

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