Calculating Emulsifier Ratio for Target HLB

To determine the ratio of two emulsifiers needed to achieve a specific required HLB (RHLB), you can use a simple formula based on their individual HLB values.

You have:

• Required HLB (RHLB) for your oil phase = 8.5
• HLB of Polysorbate 20 (Tween 20) = 16.7
• HLB of Sorbitan Oleate (Span 80) = 4.3

Let's calculate the percentage of the high-HLB emulsifier (Polysorbate 20) in the blend first. The formula is:

% High HLB Emulsifier = ((RHLB - HLB of Low HLB Emulsifier) / (HLB of High HLB Emulsifier - HLB of Low HLB Emulsifier)) * 100

Plugging in your values:

% Polysorbate 20 = ((8.5 - 4.3) / (16.7 - 4.3)) * 100
% Polysorbate 20 = (4.2 / 12.4) * 100
% Polysorbate 20 ≈ 0.3387 * 100
% Polysorbate 20 ≈ 33.87%

Once you know the percentage of Polysorbate 20, you can find the percentage of Sorbitan Oleate by subtracting from 100%:

% Sorbitan Oleate = 100% - % Polysorbate 20
% Sorbitan Oleate = 100% - 33.87%
% Sorbitan Oleate ≈ 66.13%

So, to achieve a combined HLB of 8.5 using Polysorbate 20 (Tween 20) and Sorbitan Oleate (Span 80), your emulsifier blend should consist of approximately 33.87% Polysorbate 20 and 66.13% Sorbitan Oleate.

Keep in mind that this calculation determines the ratio of the two emulsifiers within the emulsifier blend itself, not the total percentage of the emulsifier blend in your final formulation. The total percentage of the emulsifier blend needed in your formulation will depend on the percentage of the oil phase you are emulsifying. A common starting point is to use 10-20% of the oil phase weight as the total emulsifier blend weight, but this may need adjustment based on your specific formula and desired stability.