Water + fats + NaHCO3 = ? = moisturizer

In science class we make a simple moisturizing cream by melting stearine, mixing it with warm oil, hot water and adding a little sodium bicarbonate.

The curriculum says the students should learn about common components in cosmetics, and make a cosmetic product themselves, but the chemical knowledge we focus on is emulsifiers, and I have yet to get a conclusive answer on what really happens in the “experiment” we actually do.

I can do some qualified guessing, and hardly any of the students will ever discover if I’m wrong, and even fewer will attempt to use that wrong knowledge for anything practical, but I hate when I’m not imparting perfect truths to them.

I’d like to be able to say: “This is what happens, and then these compounds act as emulsifiers.” Anyone able to tell me the answer, or at least offer a more qualified guess?

I’m sorry, but “stearine” doesn’t really mean anything (rather, it means too many things). Did you use stearic acid, glyceryl (mono- and di-) stearate, or glyceryl tristearate?

Stearic acid will combine with bicarbonate to form sodium stearate, which is a classic emulsifier (well, it’s soap), but I’d imagine the yield would be very low. OTOH, it only takes a tiny percentage of sodium stearate to stabilize an emulsion containing glyceryl monostearate. It’s more usual to use sodium carbonate in such an application.

I’m sorry I can’t be more help, but this isn’t much information. Did you really just mix them like that? Or did you melt the oil ingredients together, dissolve the bicarbonate in water, and add water to oil, as I would expect?

In Norwegian stearin is Glyceryl tristearate, and wikipedia gave me the impression stearine had the same single meaning in English. The ingredient, however, is a chunk of candle, labled 100% stearin, and I suppose candle making standards don’t necessarily stand up to chemical scrutiny.

The process followed is to melt a piece of candle (about 16 grams) in an 80 C waterbath, mix it with .5 dl of oil (olive and soy) heated in the same bath, add 1.5 dl of boiling water, and then a quarter teaspoon of “Natron”, which according to the lable is NaHCO[sub]2[/sub], and then stir until you have a cream.

I meant NaHCO[sub]3[/sub] of course.

“Stearin” most commonly refers to glyceryl tristearate, yes, but to avoid confusion we also call that “tristearin.” Candle-makers, however, almost always use the word “stearin” to refer to stearic acid; they call tristearin “tallow.” Stearin candles are much harder, shinier, longer burning, and easier to make than tallow candles.

And I can see how this works now. Boiling water will allow stearic acid to mix readily with all ingredients, and using bicarbonate instead of carbonate will (I think) limit the reaction so you don’t need to worry so much about stoichiometry and safety (pH is around 9 instead of 11+).

Incidentally, a common ingredient in commercial creams and lotions is “glyceryl monostearate SE” – the SE means “self-emulsifying,” and indicates the addition of stearic acid and sodium stearate.

Sheesh, I just looked this up in my dictionary, both the dead tree version and online and it confirms what you say, with one listing for “stearin (chemistry) - tristearin”, and one for “stearin (technical) - a mix of stearic and palmitic acid”.

At least now I won’t misinform the kids with my own false assumption that candles are made from glyceryl tristearate. Also I can inform the other teachers, although they probably already know, or won’t be as excited as me. :smiley: