An o/w cream contains 9.5% (w/w) of emulsifier and has a required HLB of 11. Thesurfactants in the cream are sorbitan tristearate (Span 65) and polyoxyethylenesorbitan monopalmitate (Tween 40). If you prepare 120 g of the o/w cream,estimate the mass of each surfactant required to prepare the cream. [HLB (Span 65)= 2.1; HLB (Tween 40) = 15.6.
Question
An o/w cream contains 9.5% (w/w) of emulsifier and has a required HLB of 11. Thesurfactants in the cream are sorbitan tristearate (Span 65) and polyoxyethylenesorbitan monopalmitate (Tween 40). If you prepare 120 g of the o/w cream,estimate the mass of each surfactant required to prepare the cream. [HLB (Span 65)= 2.1; HLB (Tween 40) = 15.6.
Solution
To solve this problem, we first need to understand that the Hydrophilic-Lipophilic Balance (HLB) is a measure of the degree to which a surfactant is hydrophilic or lipophilic. The required HLB of the cream is given as 11.
The HLB of the surfactants are given as: HLB (Span 65) = 2.1 HLB (Tween 40) = 15.6
We can use these values to create a weighted average to find the ratio of the two surfactants that will give us the required HLB of 11.
Let's denote the weight fraction of Span 65 as 'x' and the weight fraction of Tween 40 as '1-x'.
We can set up the following equation:
2.1x + 15.6(1-x) = 11
Solving for 'x' gives us:
x = (11 - 15.6) / (2.1 - 15.6) = 0.35
So, the weight fraction of Span 65 is 0.35 and the weight fraction of Tween 40 is 0.65.
The total mass of the emulsifier in the cream is 9.5% of the total mass of the cream, which is 120g. So, the total mass of the emulsifier is 0.095 * 120g = 11.4g.
Therefore, the mass of Span 65 required is 0.35 * 11.4g = 3.99g and the mass of Tween 40 required is 0.65 * 11.4g = 7.41g.
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