Span 80 vs Span 60: choosing sorbitan esters for oil-phase stability
Span 80 and Span 60 are close in HLB — 4.3 versus 4.7 — but they are not interchangeable. Span 80 (sorbitan monooleate, CAS 1338-43-8) is an amber viscous liquid with an unsaturated oleate chain; Span 60 (sorbitan monostearate, CAS 1338-41-6) is a waxy solid with a saturated stearate chain. Physical form, not HLB, usually decides the choice.
Side-by-side specifications
The specification table makes the difference concrete, and the two rows that matter most in practice are appearance and saponification value. Values below are per manufacturer TDS.
| Property | Span 80 (VS-201A) | Span 60 |
|---|---|---|
| Chemical name | Sorbitan monooleate | Sorbitan monostearate |
| CAS number | 1338-43-8 | 1338-41-6 |
| HLB | 4.3 | 4.7 |
| Appearance at 25 °C | Amber viscous liquid | Slightly yellow waxy solid |
| Fatty chain | Oleate (unsaturated C18:1) | Stearate (saturated C18:0) |
| Acid value | < 4.0 mgKOH/g | ≤ 8 mgKOH/g |
| Saponification value | 140–160 mgKOH/g | 240–270 mgKOH/g |
| Ester value | Not specified | 135–155 mgKOH/g |
| Hydroxyl value | 220–260 mgKOH/g | Not specified |
| Moisture | < 1.0 % | ≤ 1.5 % |
| Density | 1.029 | Not specified |
| Thermal value on TDS | Flash point 210 °C | 52–54 °C |
| Ionic character | Nonionic | Nonionic |
How the two behave in an oil phase
Sorbitan monooleate dissolves readily in mineral oil, ester base stocks and most organic solvents at ambient temperature, so it can be stirred into a finished oil phase without heating and it does not contribute structure or body to the product. That is precisely what an oil-based release agent or an oil-based cutting fluid usually wants: an emulsifier that controls trace water and stabilises any added polar component while leaving the fluid thin, clear and pourable across the storage temperature range. The unsaturated oleate chain has a kinked geometry that resists close packing, which is the molecular reason the material stays liquid and why it rarely triggers crystallisation haze on cold storage.
Sorbitan monostearate behaves differently because its saturated stearate chain packs tightly. The material must be melted into the oil phase, which means the process needs a heated stage, and on cooling it can co-crystallise with waxes and other saturated components already present. In some products that is a defect — haze and sediment in a clear release agent — and in others it is the point, because the same crystallisation gives body to creams, pastes and thicker lubricant systems, and it raises the consistency of a W/O emulsion without a separate thickener. Formulators therefore choose the stearate when structure is wanted and the oleate when fluidity is wanted, treating the 0.4-unit HLB difference as almost incidental.
Selection guidance by system
Formulators working on oil-based release agents, oil-based cutting fluids and invert-emulsion systems that must stay fluid generally start from sorbitan monooleate, using it alone as the lipophilic stabiliser for trace and added water, or as the low-HLB anchor in a blend with a high-HLB partner such as T80 at HLB 15.0. Textile softener and fibre finish concentrates that are applied from an aqueous bath also tend to favour the oleate, because it emulsifies easily at the dilution stage and does not leave a waxy deposit on guides and rollers.
Sorbitan monostearate earns its place where the finished product is a paste, a cream or a bodied W/O emulsion, where a mild structuring effect is wanted in the oil phase, or where the application temperature is high enough that the melting behaviour is irrelevant and the tighter packing simply gives a more robust interfacial film. A practical middle path exists as well: blending the two lets the oil phase be tuned for consistency while the blend HLB stays inside the narrow 4.3 to 4.7 band, which means a consistency change does not force a rebalance of the rest of the emulsifier package. Whichever route is taken, the change should be evaluated in the actual formulation, including a cold-storage cycle, rather than on HLB arithmetic alone.
Sourcing note
Both grades are established commodity chemistries, so the difference between suppliers shows up in batch consistency rather than in the datasheet: acid value drift, colour, and moisture are the parameters that most often explain why a new lot behaves differently in an oil phase that was previously stable. Qualification of any alternative source should include a specification review against the incumbent TDS, a recent-batch COA, and a side-by-side test in the real formulation covering both fresh appearance and cold-storage behaviour.
Frequently asked questions
Is Span 60 interchangeable with Span 80?
Not directly. Sorbitan monostearate (Span 60, HLB 4.7) and sorbitan monooleate (Span 80, HLB 4.3) sit close on the HLB scale but differ in physical form — Span 60 is a waxy solid, Span 80 an amber viscous liquid — and in saponification value, 240–270 versus 140–160 mgKOH/g per manufacturer TDS. Substituting one for the other changes handling, melt-in procedure and low-temperature behaviour even when the HLB target is met.
Which sorbitan ester is better for low-temperature storage?
Sorbitan monooleate stays liquid and is the usual choice where the finished product must remain pourable and clear at low ambient temperature, such as oil-based release agents shipped to cold climates. Sorbitan monostearate is a waxy solid at room temperature and its saturated stearate chain can promote crystallisation and haze in oil phases held cold.
Can Span 60 and Span 80 be blended?
Yes. Blending the two shifts blend HLB only slightly, between 4.3 and 4.7, but it allows the consistency and crystallisation behaviour of the oil phase to be tuned: the stearate contributes structure and body, the oleate keeps the system fluid. The blend is prepared by melting the Span 60 into the oil phase first, then adding Span 80.