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Lactic acid emulsion not stable
I am having a stability problem with emulsions made with lactic acid.Details of the emulsion:pH: 4.5 - 5Oil Phase:20-25%Lactic acid 1%Sodium Lactate 2%Emulsifiers, (4 – 5 weight %)tried: Olivem 1000, Glycerin Monostearate, Emusan IIOther solid organics: Cetyl Alcohol 1 - 3%Cetyl Palmität 1- 3%Plus various humectantsThis is for a natural cosmetic and so the emulsifiers need to fall into that category. The emulsion is stable for a few days then turns watery.I did produce a sample with 9% Olivem as the emulsifier the other day and I am seeing what it will do. So far it is not watery…but so were the others in this time frame.Any suggestions?Mike -
7 Replies
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Well, the type of oils you use matters for calculating the HLB.
Also, can you tell us what you consider a Natural emulsifier? There isn’t a legal definition for it so you can pretty much call any emulsifier “natural” if you want. -
You’ll need an emulsifier that can cope with high salt content. For these type of products typically Acid Stable GMS (usually glyceryl stearate with PEG-100 Stearate), Polawax GP200 or the phosphate esters are used. Good luck finding ‘natural’ alternatives.
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You may use a mix of those emulsifiers. Try to mix a high HLB emulsifier with a low HLB one. That helps stabilizing even if you didn’t calculate the required HLB. But the ideal is to calculate your oil phase required HLB and then pick the emulsifiers most fittable to your formula.
Make clear what does natural mean to your company. Because PEG-40 hydrogenated castor oil is natural BUT it is excluded from some lists due to the EO portion. -
Thanks for the feedback Fellows,The oil mixture is Sheabutter, sunflower oil, aprocot kernal oil and almond oil, Without the lactic acid there is not a stability Problem with this mixture. The stability Problem does not arise until lactic acid is also included into the formula.Excuse me for not being clearer on the term “natural” emulsifier. I do realize that this tends to be a vague area and open to a bit of interpertation.The defination that I can put forward to this term is an emulsifier that is derived from a plant based substance that occures in nature …such as Glycerin Monostearate. One finds the Steric acid bound up in a triglycerid often in oils. Remove the other two fatty acids and there is Glycerin Monostearate. Such a molecule can often be found in nature.Polyethyleglycol (PEG) emuslifiers would be something that I would not considered a natural emulsifier because, to the best of my knowledge (please correct me if I am wrong), The PEG series is not a species that occures in nature.As far as the HLB for the emulsifier, There is only 20 something % oil in the mixture and a O/W emulsion has the better feel. An emulsifier with a HLB under 7 starts toward the W/O mixture and I begin to notice that “Watery” feeling in the creams. Olivem 1000 is about HBL 9 and gives a nice feeling when the creams are applied. I have not yet found a “natural” ( there is that loosly defined word again) higher HLB emulsifier such as Tegomuls ( Which I really like and use in unpreserved creams) that will work with the preservative Rokonsal that I use.
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Mike, have you considered the use of sodium lactoyl lactate? This is an entriely different animal, so to speak, with entirely more powerful emulsifying properties than “sodium lactate”.
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Hi chemicalmatt ,Thanks for the suggestion. I did not consider that.The sodium lactate is in the mix because it and the lactic acid form a buffer system to keep the pH in the acidic region. There is also urea in the mixture. Should the mixture be warmed up to much…like left on or near a radiator… it might reach a temperature where the urea breaks down and forms ammonia. If the system is not buffered, this can cause a rise in the pH and render the preservative, Rokonsal, ineffective.The lactoyl lactate would not be the conjugate base to the lactic acid. However perhaps it can be included as part of the emulsifier and see how it behaves under these conditions. I need to find it for sale first.
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Makes sense, Mike. I thought Stepan made this creature, Even better might be the Pationic lactylate surfactants from R.I,T.A., which work well as primary emulsifiers, though the R.I.T.A. literature strangely doesn’t mention that. Pationic SSL is what I remember using (stearoyl lactylate). I can also tell you I remember an article years ago noting that lactic acid and its salts actually stabilize urea from hydrolytic decomposition, so you are probably in good shape here. The old 10% Urea skin-care creams used that trick.
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