Tuesday, July 7, 2009

Better crafting through chemistry: Stearic acid

Oh, stearic acid, how we love you as a thickener! Inexpensive and multi-functional, you make a lotion become a decadent cream!

Stearic acid is a saturated, long chain fatty acid with 18 carbon molecules, which is to say it is a chain of carbons and hydrogens with a carboxyl group (that COOH you see at the end of the chain) at the head. It's called an acid because this carboxyl group is called a carboxylic acid. 

You might remember a picture of a similar molecule in the esters (IPM) post. An ester is a chain with a carboxyl group where the H of the OH joins up with the OH of an alcohol to create an ester and water. If you bring an alcohol to stearic acid and they undergo esterification, you get an ester called glycol stearate or glycol distearate!

Is stearic acid an emulsifier? No, but it can help to stabilize an emulsion and it's a great thickener for our lotions. It is considered as part of the oil phase in the HLB system - its HLB value is 15.5 - and it has a melting point of 69.6˚C, which is why we must heat and hold our lotions at 70˚C or higher when using stearic acid. (We should do this all the time, but it's especially important when we're using stearic acid or a butter or oil that contains stearic acid!)

You're probably quite familiar with how to use stearic acid in lotions...it's suggested up to 5%, but I like to use it at 2 to 3%. The more you use, the thicker the product will be. You can add it to shampoo and conditioner bars to make it more solid, although cetyl alcohol is probably a better choice as it works in conjunction with the cationic quat compounds to offer more conditioning. Because it is saturated, it is considered resistant to rancidity, so it's got a long shelf life.

A lot of people note stearic seems to offer more drag than cetyl alcohol, and it feels waxier. The more you add, the more of this effect you're going to find in your lotions.

You will also find stearic acid in our butters, like shea and mango butter. It has the same qualities in that butter as it does as a stand alone ingredient. 

Join me Thursday for more fun with fatty acids and alcohols when we meet cetyl alcohol!

34 comments:

pearlyn said...

stearic acid is only meant to be use in conjunction with polawax, it can't be used in conjunction with btms or cationic stuff?

Susan Barclay-Nichols said...

You can use stearic acid with cationic emulsifiers, but the cationics work better with cetyl alcohol. Cetyl alcohol boosts the substantivity of the BTMS on your hair or skin when used at 50% of the BTMS amount.

So you can use stearic in conjunction with any emulsifier you wish, but if you're using a cationic emulsifier, cetyl alcohol is the better choice if you want substantivity.

alicia said...

Would stearic acid be enough of a co-emulsifier in combination with the soy lecithin or glyceryl stearate or sorbitan stearate.. for a stable cream?

Anonymous said...

I have tried lecithin with stearic acid and it works nice. You can also try lecithin and cetyl alcohol.

jenna said...

Do you HAVE to use steric acid or cetyl alcohol when making lotions or creams? Even though I already use btms?

Susan Barclay-Nichols said...

Hi Jenna. No, but you can see the difference when you do!

jenna said...

Have you ever heard of anyone being allergic to stearic acid or the cetyl alcohol?

Anonymous said...

which emulsifer to be used for stearic acid which doesnot generate foam,

Susan Barclay-Nichols said...

Hi Anonymous. Could you please review your comment to include a name or I will have to delete it?

The classic combination is TEA and stearic acid, which creates a soap. It will always foam. Stearic acid has to be used with TEA to be an emulsifier, so not using it with TEA means it isn't an emulsifier.

Anand Mandhane said...

Hi Susan. You are doing a great work by writing this blog. It is simply divine as you are sharing such a great knowledge literally free.
I am struggling with Stearic/TEA combination. With little variation in TEA proportion, the appearance and consistency of cream changes drastically. I also use GMS in my recipes.. Is it compulsary to use TEA whenever stearic acid is there ??? Can I skip TEA and use other emulsifiers like Cetareth 20 etc ??
Thanks a Lot !!!

Heather said...

Can Stearic Acid be substitued for Cetyl alcohol in a shampoo bar?

Susan Barclay-Nichols said...

Hi Heather! Take a look at this post...
Road Trip essentials: Shampoo bars.

Starr said...

Pamela Crenshaw
Dear Susan I am just starting out making my own body butters ect so thank you for all this awesome info. My question-I need some stearic acid today so can I find it in any craft store or like whole foods I can order it online but I don't have time to wait for delivery?

Susan Barclay-Nichols said...

Hi Starr. I don't think you can get stearic acid at hobby stores or whole foods. You will want to order if you want to use it.

Teri Pearman said...

Have you ever had issues with stearic acid causing tiny lumps in finished products? It doesn't show up immediately but after a week or so...Using it with coconut oil and almond oil

Susan Barclay-Nichols said...

Hi Teri. No, I have never had this problem. I'd need to know more about your recipe in percentages and the process you followed to be able to help further.

Teri Pearman said...

I'm trying to create a creamy facial cleanser that doesn't have water and is the consistency of cold cream. I used 2 oz of palm oil and 2 tbs of almond oil. I added a 3 tbs stearic acid 1 tbs of emulsifying wax and 1 tbs of candellia wax. I was just experimenting but the texture was perfect for a week then is developed little lumps. The lumps dissolve when you rub the product in your hands but I would like to figure out what's causing the lumps - which are about the size of the stearic acid before it melts. Thanks for your help!

Teri Pearman said...

My process was to heat until the waxes melted the as it cooled I mixed with a mixer. Turned ou nice and creamy

vamsi ghf said...

can some one explain me how to mix lecithin and stearic acid to form a pourable solution

Susan Barclay-Nichols said...

Check out the posts on the HLB to learn how to combine these two ingredients as an emulsifier.

debi rosin said...

Hello, I have a question about Stearic Acid in lotion. Not doing my homework/research, I found a recipe that used SA, I liked the recipe, so I thought, and I ordered a lot of SA. I have since read your article on SA and Cetyl Alcohol. Now I know why my lotion is heavier than I want. Can I alter the amount of water and or BTS and still use the SA? I am including the formula for your review. I would also like to eliminate the Citic Acid if possible. . . Thanks for all you do. .
Recipe in grams
1.25 citric acid
5 hydrovance
10 stearic acid
21 BTMS-50
7 mango butter
16 avocado oil
19 apricot kernel oil
10 jojoba oil
5 shea butter
16 macadamia oil
388 water
3.5 Germall plus
8 fragrance oil/essential oil

Susan Barclay-Nichols said...

Could you please write up your recipe in percentages and repost this? You don't need the citric acid, so feel free to leave it out.

debi rosin said...

0.2% Citric Acid
1% Liquid Glycerin
2% Stearic Acid
4.2% Emulsifying Wax
Sure. . . and thanks for the tools to do this. . .

1.4% Mango Butter
3.2% Avocado Oil
3.8% Apricot Kernel Oil
2% Colorless Jojoba Oil
1% Shea Butter, Refined
3.2% Sunflower Oil
76.9% Distilled Water
0.7% Germaben II
0.2% Pixie Dust Fragrance Oil
0.1% Jasmine Fragrance Oil
0.2% Vanilla Cream Fragrance Oil

debi rosin said...

OOps, I hit the enter button in the wrong place. . . also I subbed the glycerine for the hydrovance and the sunflower oil for avocado oil.

0.2% Citric Acid
1% Liquid Glycerin
2% Stearic Acid
4.2% Emulsifying Wax
1.4% Mango Butter
3.2% Avocado Oil
3.8% Apricot Kernel Oil
2% Colorless Jojoba Oil
1% Shea Butter, Refined
3.2% Sunflower Oil
76.9% Distilled Water
0.7% Germaben II
0.2% Pixie Dust Fragrance Oil
0.1% Jasmine Fragrance Oil
0.2% Vanilla Cream Fragrance Oil

debi rosin said...

oops again. . . I subbed the sunflower oil for macadamia oil, not avocado oil as stated above. . . I think I got it right this time.

Susan Barclay-Nichols said...

A few thoughts...
Why are you using tiny bits of so many oils? Pick one or two that offer qualities you like and use them. You aren't getting the benefit of any oil at 2%.

What are you going for here? This really is all over the map. Pick a goal and an end skin feel and work towards that. If you want it thinner, take out the stearic. Take out the butter if you want it thinner.

BrandoVapes said...

Will overheating Stearic Acid cause it to be lumpy (small particles) ?

This doesn't happen often, maybe 1 out of 15 batches (60+ Gallons at a time)

Is there a certain temp range the Acid needs to be at before it can be mixed in to a cream base?

Susan Barclay-Nichols said...

Hi BrandoVapes! Without knowing the details of your recipe and temperature and such, it's hard to answer your questions. Stearic acid crystals are more about the cooling of the product than the heating, generally. Take a look at some sample recipes on this blog containing stearic acid to see how we use it in products. Again, I can't really answer any of this without all those details!

Brandon Curtis said...

100lbs of Stearic Acid Beads
30 Gallons of Hot water
2 Gallons soy bean oil
3 Gallons Calimide O

Other chemicals are confidential..

Skin Care Manufacturer.

I think I might have had the fire too high or something...the base looks "ok" just abit grainy

Last time it happened it hardened up on the top and bottom layer and was liquid still in the middle

We dont have a temp gauge but I am grabbing one today after work.

I might have answered my question in the comment, but any input would be fantastic...

Brandon Curtis said...

BrandoVapes and the account that just posted are the same...forgot to sign in with the other...

Brandon Curtis said...

We have been making it the same way for 40+years, and they changed the stearic from triple press flakes to the little beads about a year and a half ago

Susan Barclay-Nichols said...

Hi Brandon. I'm sorry, but without all the ingredients by weight and listed in percentages, I really can't help. There are just too many variations. I have a feeling it has to do with the cool down process of the product and/or the new flakes, which could be radically different from the previous stearic acid, but it really could be anything.

My best suggestion is to contract with someone with whom you will share your ingredients and see what they think!

rounita devianasari said...

Hi Susan, your blog is helpful. Thank you.
Now I formulating Cold Cream for Cleansing purpose, but I still unclear about this kind formulation.
I'm using Stearic acid - TEA but I can't get thinner formula than I change to Sorbitan stearate, but the problem is my formulation is separate and less opaque. Here is my formulation :
5% Ethylhexyl Palmitate
4% Isohexadecane
3% Dimethicone
3% Sorbitol
3% Sorbitan Stearate
1% Butyrospermum parkii oil
0.5% Sunflower oil
0.08% Acrylates/C10-30 Alkyl Acrylates Crosspolymer
o.1% Tocopheryl acetate
0.05% Disodium EDTA
0.5% mix of Glyceryl Stearate & PEG-100 Stearate
0.3% Cetearyl alcohol
0.5% mix of phenoxethanol & Ethylhexyl glycerin
Aqua add 100%

What dou you think about this formulation.
if you have an article or link about cold cream formulation please share.

Susan Barclay-Nichols said...

Hi Rounita. This isn't a cold cream. A cold cream is a water in oil product. This is an oil in water lotion. You've made a nice lotion here with a very small oil phase. I'm not sure what you want me to offer comment on for the recipe. If your recipe is separating, you aren't using enough emulsifier. The only answer is to increase it and see what happens.

You can do a search online for cold cream recipes and surely find one. I've never made one as I prefer to use surfactant based cleansers and make oil-in-water lotions. If you find something interesting, please come back and share it as I'm sure other readers want to know more about this, as do I.