Tween 80 vs Tween 40: choosing a polysorbate for your emulsion

Ask two formulators the same question and both names come back: Tween 80 and Tween 40. Both are ethoxylated sorbitan esters, both sit in the polysorbate family, and both are sold as nonionic emulsifiers. The difference that decides your formulation is not the trade name. It is which fatty acid is attached to the sorbitan ring, because that is what sets how oil-loving the tail is.

The short answer

Tween 80 and Tween 40 are members of one series, built the same way every time: a sorbitan ring carries a fatty acid, and ethylene oxide units are added to the remaining hydroxyls to make the molecule water-soluble. The fatty acid sets the tail; the ethylene oxide count sets the head. Choosing between two members of the series is therefore a question about your oil phase, not about which grade is stronger.

The practical consequence is that the only reliable basis for a comparison is the supplier specification for the exact grade in front of you, plus a bench test in your own water and your own oil. Grade-level numbers are not transferable between suppliers, and they are not transferable between members of the series either.

Where the two names come from

Sorbitan esters are usually met under the Span name, and their ethoxylated versions are usually met under the Tween name. A polysorbate is the same molecule described by chemistry instead of by trade name. The number in the trade name is a series index, not a performance rating: it identifies a particular combination of fatty acid and degree of ethoxylation. A higher number does not mean a stronger emulsifier.

On this site the two reference points for reading the series are Tween-80 (Polysorbate 80), documented as an oil-in-water emulsifier and solubiliser, and Span-80, the non-ethoxylated sorbitan ester documented as a water-in-oil emulsifier. The pair shows the logic in one step: ethoxylating the same backbone walks the molecule from the oil-favouring end toward the water-favouring end.

What actually differs inside the series

• Fatty acid identity. Laurate, palmitate, stearate and oleate tails differ in chain length and in unsaturation. A longer saturated tail is more lipophilic; an unsaturated tail of similar length behaves differently again in crystallisation and in cold storage.
• Degree of ethoxylation. The number of ethylene oxide units added to the sorbitan hydroxyls sets how polar the head is, and therefore how water-soluble the molecule becomes.
• The resulting balance. The hydrophilic-lipophilic balance is the outcome of those two choices. It is a property you read off a specification, not a knob you can set independently of the chemistry.
• Physical form at room temperature. Members of the family are supplied as viscous liquids, greases or waxy solids, which changes how they are pumped, weighed and charged to a vessel.

Read the balance, not the label

The comparison that pays is between the balance of the candidate grade and the balance your oil phase requires. Two grades from the same series often succeed or fail for the same reason: the required balance of the oil, solvent and water combination is not the one the chosen grade provides. That is why blending two members of a series is normal practice - a blend lets you land between two available points instead of settling for the nearer one.

If the required balance for your oil phase is known, screen the candidates against it before ordering samples. If it is not known, the bench sequence below will tell you more in an afternoon than any side-by-side datasheet comparison. The underlying chemistry is set out in how the hydrophilic head group drives the balance.

How to run the comparison in your own lab

• Dilution test. Emulsify each candidate into your actual oil at your intended dose, and watch whether the emulsion forms at the temperature and agitation your plant can actually deliver.
• Water quality. Repeat in the water you will really use. Uncharged nonionic heads tolerate hardness and electrolyte load better than charged heads, but the balance that works can still shift with ionic strength.
• Storage and temperature cycling. Hold samples at the top and bottom of your storage range and check for creaming, settling, gelling or phase separation. An emulsion that only holds at room temperature is not a finished choice.
• Charge and handling. Confirm the grade can be pumped, melted or pre-dissolved with the equipment you have. Ambient form is a real selection variable on a plant floor, not a footnote.
• Dose and cost in use. Compare at equal delivered performance rather than at equal mass, because two grades on different balance points will not do the same work at the same loading.

Why no balance number appears for these grades

Polysorbate grades are frequently quoted with a balance figure, and it is tempting to sort a table by that single column. This site does not publish one for the polysorbate grades referenced above, because that value is not part of the specification record we hold for them. Where a value is not in the documented record, we leave it out rather than fill the gap with a borrowed figure. Other grades on this site do carry a published balance when the client record includes it, so the omission here is about the evidence, not about policy.

Two examples where the value is documented: Emulsifier EL-40 (PEG-40 Castor Oil) is published with an HLB of 13-14, and Emulsifier SG-10 with an HLB of 12-13 - both nonionic and both positioned on the water-favouring side. If you need a balance figure for a formal screening step, request it from the supplier together with the rest of the grade data, and confirm it on the bench before it enters a formulation record.

A comparison framework you can reuse

Where these grades are used

Ethoxylated sorbitan esters appear across cosmetic, pharmaceutical, food and industrial systems, usually as the water-favouring half of an emulsifier pair and often as a solubiliser for oils that must be carried in an aqueous phase. The pairing logic - a lipophilic sorbitan ester with a more hydrophilic ethoxylated partner - is the same one that governs emulsifier selection for agrochemicals and the choice between nonionic and anionic surfactants. Where the job is to bring a single oil-soluble component into clear aqueous solution rather than to hold an emulsion, a dedicated grade such as CO40 Solubilizer is the usual starting point.

Specification block: what is documented here

For transparency, this is what the published record contains for the two reference grades, and what it does not contain:

• Tween-80 (Polysorbate 80): CAS 9005-65-6; conforms to HG/T 3510; amber viscous grease at 25 degrees Celsius; hydroxyl value 65-82 mgKOH/g (GB/T 7384); saponification number 43-55 mgKOH/g (HG/T 3505); acid value 2 mgKOH/g or below (GB/T 6365); water content 2% or below (GB/T 7380).
• Span-80: CAS 1338-43-8; conforms to HG/T 3508; amber viscous grease at 25 degrees Celsius; hydroxyl value 190-220 mgKOH/g (GB/T 7384); saponification number 140-160 mgKOH/g (HG/T 3505); acid value 8.0 mgKOH/g or below (GB/T 6365); water content 1.5% or below (GB/T 7380).
• Tween-40 / polysorbate 40: no specification block is published on this site, and none is reproduced here. Treat any grade-level figure you find elsewhere as supplier-specific and verify it against a lot-specific certificate before it enters a formulation record.

Related reading

Continue with what an emulsifier is and how the types differ, then the broader selection notes for Lipalbin and textile dyeing auxiliaries.

Next step

Grade choice is fastest with your oil phase, your target emulsion direction and your water in hand. Send us the details and we will shortlist the grades that sit near your required balance.