Span 80 vs Tween 80: which emulsifier for which system?
The rule is simple: Span 80 (sorbitan monooleate, HLB 4.3) is oil-loving and stabilises water-in-oil (W/O) systems; Tween 80 (polysorbate 80, HLB 15.0) is water-loving and stabilises oil-in-water (O/W) systems. They share the same sorbitan-oleate backbone — Tween 80 adds about 20 ethylene oxide units — which is why they blend so effectively for intermediate HLB targets.
Side-by-side properties
| Property | Span 80 | T80 (Tween 80) |
|---|---|---|
| Chemical name | Sorbitan monooleate | Polyoxyethylene (20) sorbitan monooleate |
| CAS number | 1338-43-8 | 9005-65-6 |
| HLB | 4.3 | 15.0 |
| Appearance | Amber viscous oily liquid | Light yellow to amber oily liquid |
| Water solubility | Insoluble; soluble in hot oils and organic solvents | Soluble in water, methanol, ethanol, isopropanol |
| Acid value | < 4.0 mgKOH/g | ≤ 2.0 mgKOH/g |
| Saponification value | 140–160 mgKOH/g | 65–80 mgKOH/g |
| Emulsion type stabilised | Water-in-oil (W/O) | Oil-in-water (O/W) |
Application mapping
Choose Span 80 when the continuous phase is oil: oil-based release agents, oil-based cutting fluids, invert-emulsion drilling fluids, W/O lubricant systems, and as the lipophilic anchor in emulsifier blends. Sorbitan monooleate also serves as a softener and antistatic component in textile applications and a lubricity additive in leather fatliquors.
Choose Tween 80 when the continuous phase is water: semi-synthetic metalworking fluid concentrates, industrial cleaners, aqueous textile auxiliaries, and any O/W emulsification, wetting or dispersing task. Polysorbate 80 also acts as a solubiliser, carrying small amounts of oil-soluble additives into clear aqueous systems.
Why the pair works better than either alone
Because both molecules share the sorbitan-oleate structure, they pack together tightly at the oil–water interface: the sorbitan ester buries its oleate tail in the oil while the ethoxylated partner extends its polyoxyethylene chains into water. This mixed film resists rupture better than a single-emulsifier film, and the weight ratio between the two sets the blend HLB anywhere from about 5 to 14 — one pair of raw materials covering nearly the whole O/W formulation range. A 50:50 blend, for reference, gives an HLB of about 9.7.
Sourcing note
Industrial-grade sorbitan monooleate and polysorbate 80 are commodity chemistries, but batch consistency — acid value, colour, water content — is what separates suppliers in practice. Whichever source is used, qualification should include the TDS specification review, a recent-batch COA, and a parallel emulsification test against the incumbent material in the actual formulation.
Frequently asked questions
Can Span 80 and Tween 80 be used together?
Yes — pairing them is standard practice. Blending sorbitan monooleate (HLB 4.3) with polysorbate 80 (HLB 15.0) lets a formulator hit any blend HLB between roughly 5 and 14 by adjusting the weight ratio, and the mixed film of the two related molecules is stronger than either alone.
Is Tween 80 the same as Polysorbate 80?
Yes. Tween 80, T80 and Polysorbate 80 all refer to polyoxyethylene (20) sorbitan monooleate, CAS 9005-65-6. Industrial, food and pharmacopoeia grades differ in purity and documentation, not in base chemistry — industrial applications use industrial grade.
Which one is better for drilling fluids?
Oil-based and synthetic-based drilling fluids are water-in-oil systems, so the low-HLB sorbitan monooleate (Span 80 type) chemistry is the relevant starting point, usually alongside polyamide-type primary emulsifiers. Polysorbate 80 is generally not used in invert-emulsion muds.