Stearic Acid Grades Explained: 1801, 1840 and 1842 in Soap, Rubber and Plastics

Stearic acid is one of the most widely traded oleochemicals, and also one of the most loosely specified in everyday purchasing conversations. Buyers ask for stearic acid and receive offers labelled 1801, 1840, 1842 or 1850, often with no further explanation. Those numbers are not marketing labels. They describe the titer and the iodine value range of the material, and they decide how the acid behaves in soap, rubber, plastics and candle blends.

What the Grade Numbers Mean

The leading part of a designation such as 1801 refers to the carbon chain convention used by the producer, while the trailing digits indicate the iodine value ceiling. Iodine value measures unsaturation: the lower the number, the more saturated the acid and the more resistant it is to oxidation and colour development. A 1801 grade is a highly saturated material with a relatively high titer. A 1842 grade tolerates slightly more unsaturation and sets at a marginally lower temperature.

Because naming conventions differ between producers and regions, two suppliers can quote the same designation and still deliver somewhat different chain-length distributions. The certificate of analysis, not the label, is the document that actually matters.

Reading a Certificate of Analysis

Four numbers carry most of the practical weight. Titer, the freezing point of the fatty acid, governs how quickly a soap bar or a candle sets. Iodine value predicts colour stability in storage and in the finished product. Acid value confirms the proportion of free fatty acid and therefore the saponification behaviour. Colour, usually reported on the Gardner or Lovibond scale, tells you whether bleaching was adequate, which matters for white soaps and light-coloured plastics.

Chain-length distribution deserves equal attention. Commercial stearic acid is not a single compound but a blend of palmitic (C16) and stearic (C18) acids with small amounts of others. A higher C18 share gives a harder, higher-melting product, while a higher C16 share can improve solubility and processing behaviour. For PVC lubricants and rubber activators, that balance affects dispersion and cycle time more than the headline purity figure does.

Matching Grade to Application

Soap and toiletries usually call for high-purity, low-iodine stearic acid with good colour. The bar needs hardness and a clean white appearance, and residual unsaturation tends to show up as yellowing over time.

Rubber compounds use stearic acid as an activator in vulcanisation. The requirement here is consistent acid value and low ash rather than premium colour, so a mid-range grade is normally sufficient.

Plastics, particularly rigid PVC, use stearic acid and its metal soaps as internal and external lubricants. Melt flow and plate-out behaviour are sensitive to chain-length distribution, which is why processors often fix a single grade and resist substitution even when a cheaper offer appears.

Candles and cosmetic butters sit between these categories. They want a firm set, low odour and predictable shrinkage, which generally points to a saturated grade with a well-controlled titer.

Sourcing Notes

Palm-based stearic acid dominates Asian supply, and the splitting and fractionation technology behind it determines how tightly a specification can be held. Buyers importing in bulk should confirm packing format, because flake, pastille and liquid forms behave differently in pneumatic conveying and in storage silos. Pastilles flow better and generate less dust. Flakes melt more easily but tend to cake in humid weather.

It is also worth agreeing on a retest period and storage condition in writing. Stearic acid is a stable material, but warm warehouses soften pastilles into a single mass, and moisture pickup can shift acid value over long storage.

About SINOFO

SINOFO Group supplies imported oleochemical raw materials, including stearic acid, lauric acid, myristic acid, palmitic acid, refined glycerin, propylene glycol and fatty alcohols, to manufacturers across Asia and beyond. We work with established producers in Malaysia and Indonesia and support buyers with specification matching, sample coordination and export documentation. If you are reviewing a grade change or comparing offers, send us your target specification and application, and our team will come back with a suitable option.