Castor derivatives for lubricants are mainly 12-hydroxystearic acid (12-HSA), hydrogenated castor oil and sebacic acid. For 12 HSA for grease, the main use is to make lithium 12-hydroxystearate, the soap that thickens base oil into a grease. Formulators therefore care about how consistently the acid reacts and what it leaves in the grease.
This article goes beyond the basic uses covered in what 12-HSA is used for.
How is 12-HSA used in grease?
The grease maker reacts 12-HSA with lithium hydroxide in a portion of the base oil. This forms the soap, which crystallises into a fibre network and holds the oil. Complex greases add another acid to the same system to raise the dropping point.
The result depends on the acid. If the 12-HSA has a lower hydroxyl content, or contains stearic acid, the soap structure changes, and the grease may come out softer, grainier or less stable. That is why grease makers watch the specification closely.
What specifications do formulators enforce?
- Acid value, which should sit close to the theoretical figure for pure 12-HSA; see the 12-HSA acid value for how to read it.
- Hydroxyl value, which shows how much of the acid carries the hydroxyl group that builds the soap structure.
- Melting range, which should be narrow and stable between lots.
- Iodine value, because unsaturation reduces oxidation stability in the grease.
- Colour, ash and moisture, because the grease plant needs a predictable saponification.
- Stearic acid and other fatty acids, which dilute the effect of the hydroxylated acid.
Why run a trial grease?
Formulators usually also run a small trial grease from the supplied lot and measure penetration and dropping point. A passing certificate and a failing grease can both occur, so the trial matters.
Which form should you buy?
12-HSA comes as flakes or powder, and hydrogenated castor oil as flakes, powder or beads. Flakes are easy to charge to the kettle, while powder dissolves faster but can be dusty. Details are in the forms of HCO and 12-HSA.
Some grease makers use hydrogenated castor oil as the starting material and saponify it themselves, which gives glycerol as a by-product. Others buy the free acid. Which route you use changes your specification, so decide it first.
Other castor derivatives in lubricants
Sebacic acid is used to make sebacate esters, which are valued as synthetic base fluids for low temperature and high performance lubricants. Castor-derived polyols and esters are also used in some industrial and metalworking fluids. Each carries its own specification, covered in castor derivative quality issues and the specification guidance in the sebacic acid article.
Because grease is a performance product, ask the supplier how it controls the process between batches, not only the final numbers. A change in hydrogenation or distillation conditions can shift the fatty acid profile while the certificate still passes. Agree to be notified of any process change, and keep a sealed sample of each lot so grease results can later be traced back to the acid that went into them.
Next step
We find Gujarat castor derivative plants, send samples for independent testing against your acid, hydroxyl and melting range limits, and supervise loading. To begin, book a free sourcing review.