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Neutralized Stearic Acid and HLB
Hi Everyone,
Please excuse the ignorance with this question but I am wanting to know how one uses the HLB equation if you are using neutralized stearic acid as the secondary emulsifier?
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13 Replies
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(primary emulsifier)/(primary + secondary emulsifier)*HLB primary emulsifier + (secondary emulsifier)/(primary + secondary emulsifier)*HLB secondary emulsifier = HLB of mixture. Primary and secondary emulsifier are in grams or alternatively weight-% of total emulsifier (i.e. % primary*HLB primary + % secondary*HLB secondary = final HLB).HLB of stearates are around 18-20 depending on counter ion. -
you don’t - salts of stearic acid are ionic, and HLB is only relevant to non-ionic emulsifiers
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@Bill_Toge i thought that was probably the case. What is the best way of working out how much of the secondary surfactant is needed then? Or is that just trial and error?
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@Pharma thanks for the formula. I do know how to work out HLB but have found Stearic Acid particularly confusing.
How would one balance the HLB when using a coemulsifier like Ceteareth 20 which has a high HLB?
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Bill_Toge said:you don’t - salts of stearic acid are ionic, and HLB is only relevant to non-ionic emulsifiers
Says how? Sure, with SLS & co. having apparent HLB values of 20-40 it doesn’t make much sense but salts of weaker fatty acids with HLB between 15 and 20 it does make sense depending on what you’re going to formulate.
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Jamjar said:@Pharma thanks for the formula. I do know how to work out HLB but have found Stearic Acid particularly confusing.
How would one balance the HLB when using a coemulsifier like Ceteareth 20 which has a high HLB?
What is confusing about stearic acid? You don’t have to determine its HLB but simply look it up. The maths afterwards is the same for all.What do you mean by balancing HLB? BTW HLB doesn’t care about high or low or co-emulsifier or primary or whatever definition we print on them. HLB is just numbers. -
@Pharma basically the confusing part is that there many cream products or formulas that are using Stearic Acid as a co Emulsifier are using a secondary emulsifier with a high HLB value such as Ceteareth 20. From my calculations I haven’t seen one where it would balance. Or am I missing something totally here?
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Stearic acid when used as coemulsifier is just added up to the oil phase (Pharma’s formula). When you use TEA-stearate as an emulsifier there’s no sense to calculate HLB, because it’s anionic. HLB system is only useful for non-ionic emulsifiers. Post an entire formula and it will be easier to comment on qualities of emulsifiers.
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In the formulas you are looking at … are they adding a base such as NaOH to create Sodium Stearate as the co-emulsifier?
If not, then Stearic Acid is more likely just being used as a thickener. If a base is listed on the LOI, then it is being used as a co-emulsifier.
And, what is the HLB of the oils in the formula?
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@MarkBroussard @ngarayeva001 I am talking about in general. What I mean is if you use a base to create TEA Stearate or Sodium Stearate, which is anionic as has been mentioned, how would you calculate the quantity of a secondary non-ionic emulsifier? Would that be trial and error? Also would the HLB of that non-ionic emulsifier even matter when being paired with an anionic emulsifier?
thanks for all the comments and help.
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As a rule of thumbs, use 1/10 anionic with regard to non-ionic. The non-ionic does most of the work, the negative charge simply adds to stability (negative charge of oil droplets causing repulsion and hence reduced coalescence).
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I understand this is not what was asked but if you want to add something negatively charged to stabilise the formula, make a non-ionic emulsion with conventional emulsifiers and add polymeric emulsifiers (Sepinov, Zen etc). The most of them are anionic and the difference in texture will be very noticeable.
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Depending on what you want to do, stearate salts can be part of an HLB calculation. Just because they are negatively charged doesn’t mean they don’t have an HLB. They may however be out of the original range which, due to the arbitrary definition by Griffin, the inventor of the system, is set at 20. The HLB system has since been evolved, alternate formulas without an upper limit are available like Davies’ approach, which is the main one used in pharmacy, or even computer models (e.g. add-on for MarvinSketch). Hence, HLB values above 20 are absolutely possible and can be used for calculations without limits. Because stearate salts aren’t, from a practical point of view, fully dissociated like SLS, they would even comply with Griffin’s method. HLB values for salts such as SLS, because of near absolute dissociation, have to be determined using alternative biphasic systems. Remember, the HLB system is based on observation and the original formula was deduced from practical experiments (hence the restriction to emulsifiers which were originally used). But then again, half the originally published HLB values weren’t even calculated but only experimentally determined. Most HLB values of today’s emulsifiers are determined the same way. Depending on the model used, different values can be obtained.There is no practical application in cosmetics for final HLB values above 20 or rather, there is no noticeable difference between a product with an HLB of 20 and one of 40. If a combination is used which has an HLB below 20, there is no reason not to apply the same formula for co-emulsifiers with an HLB >20.One limitation of calculating HLB values for stearate salts is their pH dependency in acidic formulas.
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