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Stearate base emulsion
I made one fairness cream with stearate soap.
I used Stearic acid and Potassium hydroxide and made stearate soap based cream.In that i observed that when i add little amount of citric acid solution in my formulation the stearate soap is totally separate i don’t know why it could happen if any body know kindly share with me. -
12 Replies
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First of all why would you add citric acid to the emulsion, secondly check the pH before and after the addition of the carboxylic acid and you would know why its happening. If you want to keep the pH low then use less neutralizer or add more stearic acid.
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Stearate based creams are the soaps, which could exist only at alkiline pH range.
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@ milliachemist for example if u add excess KOH then for decreasing pH u can not use stearic acid cause ur emulsion is prepared and it doesnt work, so u have to add citric acid.
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@nasrins To avoid these situations SAP values were created and are used in such situations. Its very rare that these carboxylic acids are employed as buffers for such kind of emulsions, rare means very very rare.
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so ur emulsion is prepared and the pH after neutrolizing is high. whats ur suggestion?
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If I have a similar problem and citric acid isnt working I would add a partially neutralized carbomer gel to adjust the viscosity and pH both at the same time. But this is my opinion, my perception about trouble shooting, every individual would have a different take on it.
cheers
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@vjay Try lactic acid instead of citric acid, guess monoprotic acid would work much better compared to triprotic. Although I have had no such situation till now but you can do this trial and let us all know how it goes.
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vjay, try milliachemists suggestions or you might find it easier to use a non-ionic modern emulsification system
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@nasrins, the answer is, next time, use less base, and/or use enough co-emulsifiers that destroying the Potassium Stearate with acid won’t crash the emulsion.
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@Bobzchemist Bingo!!!!!!!!!
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@nasrins, I am always careful to calculate formulas using the SAP values of the specific grade of fatty acid I will be using, in order to make sure that I don’t have to adjust the pH downward. In my experience, adjusting the pH of a finished stearic, oleic, and/or palmitic emulsion downwards has a good possibility of breaking at least some of the emulsion, due to localized acid effects.
In other words, when you add acid to a batch, unless you are adding acid diluted in a great deal of water, the area of the batch where the acid has been added has a temporarily lower pH until the acid is diluted and dispersed through out the batch. This can lead to problems if your emulsifier(s) are pH sensitive.Below a certain pH (empirically about 8.5 - 9.0) fatty acid soaps separate back into fatty acid and base. As the batch regains an equilibrium pH, you’d expect the fatty acids to re-saponify. This would not have to be a problem, except for three things:1) The acid that you’ve added is now competing for the base in the batch.2) Rapid saponification depends on heat - if your batch is too cool, it won’t happen. This is especially true with stearic acid, which needs to be molten to saponify.3) You have based your stability around the emulsification power of the fatty acid soaps, so when the soaps fall apart, so does the emulsion. Even if the fatty acid soaps re-saponify, you are going to have to go back to your original emulsification conditions to restore the batch to it’s original emulsified condition.There is one way to cope with this, and I have done it several times - you have to pH adjust your batch while it is still emulsifying. To do this, you pull a small sample, cool it down, and titrate the pH. Using the small batch amount as a guide, scale up the adjustment and add it to the larger batch. Only then can you start cooling.Hope this helps,Bob -
Dear All thanks for your suggestion i will definitely try lactic acid.
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