The main uses of stearic acid are in rubber, plastics, soap, cosmetic creams, candles, greases and pharmaceutical tablets. Each of these needs a different grade. A grade that works well in a tyre may not be pure enough for a face cream or a tablet.
As a buyer, you need to understand not only what stearic acid does, but also which grade your process requires. This article covers both, starting with what stearic acid is.
What is stearic acid?
Stearic acid is a saturated fatty acid built on a chain of eighteen carbon atoms, with the formula C18H36O2. When pure, it is a waxy solid that melts at about 69 °C.
A fatty acid is the building block of fats and oils. Saturated means its carbon chain carries no double bonds, which is what makes stearic acid a hard, stable solid rather than an oil.
Commercial stearic acid is rarely pure. It is usually a blend of stearic acid and palmitic acid, a similar fatty acid with sixteen carbon atoms. The specification sheet tells you how much of each is in the blend.
How much of each ends up in the blend depends on how the stearic acid is made.
How is stearic acid made?
Stearic acid is made by splitting fats with hot water, which releases the fatty acids from the glycerine they were bound to, and then distilling the fatty acid mixture to separate it. Unsaturated acids in the mixture can be hydrogenated to convert them into more stearic acid.
Hydrogenation means adding hydrogen across the double bonds of an unsaturated fatty acid. Oleic acid, an unsaturated fatty acid found in palm and soy oil, has one double bond, and hydrogenating it turns it into stearic acid.
Distillation then separates the acids by boiling point, which is how producers control the ratio of palmitic to stearic acid in the finished product. Older plants did this separation by pressing instead, and that is where the grade names come from.
Before the grades, though, it helps to see where the product ends up.
What is stearic acid used for?
Stearic acid is used in rubber and tyre compounding, PVC and other plastics, soaps and detergents, cosmetic creams, candles, greases and pharmaceutical tablets. Depending on the industry, it either takes part in a chemical reaction, lubricates, hardens, or helps oil and water stay mixed.
Rubber and tyres
In rubber, stearic acid works with zinc oxide as an activator during vulcanisation, the heating step that links rubber molecules together so the compound holds its shape. The two react to form zinc stearate, which dissolves in the rubber and speeds up that cross-linking. What rubber makers need most is consistency. If one delivery behaves differently from the last, vulcanisation can run faster or slower than planned, and the finished rubber changes with it.
PVC and plastics
In PVC (polyvinyl chloride), stearic acid is mostly used in the form of metallic stearates, which are salts made by reacting it with a metal compound. Zinc and calcium stearates act as heat stabilisers, protecting the polymer from breaking down at processing temperature. Our oleochemical range includes zinc stearate for this kind of use.
Soaps and detergents
Soaps and detergents are among the main uses of stearic acid. One end of the molecule is attracted to water and the other to oil, which makes it a surfactant: a substance that lets oil and water mix so dirt can be washed away.
Cosmetics and personal care
In creams and lotions, stearic acid acts as an emulsifier, meaning it helps hold the oil and water phases of the product together so they do not separate on the shelf. Here colour and odour matter as much as chemistry, because the customer sees and smells the finished product.
Candles
Fatty acids such as stearic acid have long been used in candle making, blended with wax. Candle makers look at the setting point and colour, because both show in the finished candle.
Greases, lubricants and release agents
Lithium stearate, made from stearic acid, is a standard component of lubricating greases. Calcium stearate is used as a release agent, a coating that stops a moulded part sticking to its mould, and stearic acid itself is used as a lubricant when ceramic powders are pressed into shape.
Pharmaceutical tablets and capsules
In tablet making, stearic acid is used as a lubricant and sometimes as a binder. As a lubricant it stops powder sticking to the punches and dies of the tablet press, which helps tablets come out whole and evenly hard.
Pharmaceutical grades are made to a pharmacopoeia monograph, an official specification such as the USP-NF or the European Pharmacopoeia, which sets the tests each batch must pass.
Across all of these, the same chemical name covers quite different materials, and the grade names are where buyers most often get confused.
What do single, double and triple pressed mean?
The names describe how many times the fatty acid was pressed to squeeze out the liquid, unsaturated acids such as oleic acid. Single pressed was pressed once and keeps the most oleic acid, while triple pressed was pressed three times and is the purest of the three.
In the original method, the fatty acids were chilled until the saturated acids set solid, cold pressed so the liquid acids ran out, then remelted, recrystallised and pressed again while warm. Each further pressing removed more of the liquid acids. Most production now reaches the same result through hydrogenation and distillation, but the three names are still used as grade labels.
What changes between the grades is how much unsaturated acid is left. That shows up in the iodine value, a measure of how many double bonds remain: the more thoroughly the oleic acid is removed, the lower the iodine value and the better the stability of the product. Some grades are named by use instead, such as rubber grade, which is the least refined.
Which of these a process needs depends on what goes wrong if the grade is too low.
Which grade of stearic acid suits which application?
Match the grade to the most demanding requirement of the end product: appearance and odour for cosmetics, pharmacopoeia compliance for tablets, and consistency for rubber. Buying a higher grade than the process needs adds cost without improving the product.
| Application | Grade usually chosen | What to check first |
|---|---|---|
| Rubber and tyres | Rubber grade or single pressed | Acid value, consistency between deliveries |
| Soaps and detergents | Single or double pressed | Acid value, colour |
| PVC and metallic stearates | Double or triple pressed | Iodine value, colour |
| Candles | Double or triple pressed | Titre, colour |
| Cosmetics and personal care | Triple pressed | Colour, odour, iodine value |
| Pharmaceutical tablets and capsules | Pharmacopoeia grade | Compliance with the monograph, certificate with every batch |
Whichever grade is ordered, the certificate of analysis is where a buyer confirms they received it.
What should you check on a stearic acid certificate of analysis?
Check the acid value, saponification value, iodine value, titre and colour against the specification you ordered, and for pharmaceutical use, every test the monograph requires. A figure that drifts from one delivery to the next is a bigger warning sign than any single result.
A certificate of analysis is the test report that comes with each batch. These are the figures on it that matter, and what each one tells you:
- Acid value. How much free fatty acid is present, measured by the alkali needed to neutralise it. It confirms the material is acid, not partly unsplit fat.
- Saponification value. How much alkali the material consumes in total. When it sits close to the acid value, very little unsplit fat remains.
- Iodine value. How many double bonds remain, and so how much unsaturated acid is left. Lower means purer and more stable.
- Titre. The temperature at which the melted fatty acid sets. It is a quick check that the blend of fatty acids is what it should be.
- Colour. Reported on a standard colour scale. It matters most for cosmetics and other light-coloured products.
- Carbon chain composition. The share of palmitic acid (sixteen carbon atoms) and stearic acid (eighteen carbon atoms) in the batch.
Ask for the certificate with every batch, not only the first. Comparing certificates over several deliveries is the simplest way to see whether a supplier’s product stays consistent.
Stearic acid is also the starting point for a family of related products, which buyers sometimes confuse with it.
How is stearic acid different from magnesium stearate and calcium stearate?
Magnesium stearate and calcium stearate are salts, made by reacting stearic acid with a magnesium or calcium compound. They are different materials with their own specifications, and magnesium stearate is the most commonly used tablet lubricant.
In tablets, stearic acid and magnesium stearate can do the same job, lubrication, but they do not behave the same way. Magnesium stearate lubricates very effectively but can slow how quickly a tablet breaks down and releases its drug, so formulators choose between them with that trade-off in mind.
Our pharmaceutical range includes 3F LuboMag magnesium stearate and 3F LuboCal calcium stearate, alongside stearic acid and refined glycerin.
Because the grade drives so much of the specification, it also drives the price.
What affects the price of stearic acid?
The price of stearic acid follows its feedstock, the vegetable or animal fats it is made from, and rises with each step of purification. Grade, pack size and order volume then decide where a particular quote sits.
A triple pressed or pharmacopoeia grade costs more than a rubber grade because it goes through more processing and more testing. Feedstock fats are agricultural commodities, so stearic acid prices move with oilseed and palm oil markets rather than staying fixed through the year.
For that reason we quote on enquiry rather than publishing a price list. Which leaves the practical question of what we supply.
Which stearic acid grades does 3F supply?
3F Industries Limited was founded in 1960 and makes fats, oils and oleochemicals at four plants. We sell industrial stearic acid under the Triffa name, in six grade families: cosmetic, metallic stearate and PVC stabiliser, plastic and polymer, tyre and rubber, high titre and metal powder, and speciality grades.
The table below gives the main figures for each Triffa grade. The purest grades have the lowest iodine values, and the full specification, including colour and ash, is on our oleochemicals page.
| Grade | Appearance | Acid value (min) | Iodine value (max) | Titre (°C) |
|---|---|---|---|---|
| Triffa 911 | White flakes | 210 | 0.5 | 54 to 56 |
| Triffa 951 | White flakes | 207 | 0.5 | 54 to 56 |
| Triffa 971 | White flakes | 200 | 1.5 | 58 to 62 |
| Triffa 921 | White flakes | 205 | 3.0 | 54 to 62 |
| Triffa 241 | White flakes | 198 | 3.0 | 60 to 65 |
| Triffa 811 | White flakes | 195 | 3.0 | 65 to 68 |
| Triffa 211 | Off-white flakes | 195 | 5.0 | 54 to 62 |
| Triffa 901 | Light brown to brown flakes | 185 | 9.0 | 52 to 62 |
Triffa grades are packed in 25 kg or 50 kg bags, either polycoated plastic (HDPE) or paper.
For pharmaceutical use, our stearic acid is sold as 3F LuboStear. It is tested to four pharmacopoeias: the Indian (IP), British (BP), European (Ph. Eur.) and United States (USP). It is packed in 25 kg paper bags or HDPE drums with an inner liner.
Common questions
Is stearic acid made from vegetable or animal fat?
It can be made from either. Older production used tallow, an animal fat, while vegetable sources such as palm and soy oil are also used. Our pharmaceutical stearic acid is made from vegetable oils, and we have been a member of the Roundtable on Sustainable Palm Oil (RSPO), the main global standard for sustainable palm oil, since 2014.
What is the difference between stearic acid and stearin?
Stearic acid is a fatty acid. Stearin usually refers to a solid fat, such as palm stearin, which is the hard fraction of palm oil, and the Indian tariff lists it on separate lines from stearic acid.
Is triple pressed stearic acid the same as pharmaceutical grade?
Not necessarily. Triple pressed describes how pure the acid is, while a pharmaceutical grade must also meet every test in a named pharmacopoeia monograph, so check the monograph on the certificate rather than the grade name alone.
Tell us your application and we will recommend the grade
Send us the end product, the process, the volume you buy each month and any pharmacopoeia or customer specification you work to. Our team will come back with the grade that fits and its specification sheet.