Span 20 (sorbitan monolaurate) and Span 80 (sorbitan monooleate) are both nonionic surfactants derived from the esterification of sorbitol with fatty acids. Despite sharing the same sorbitan backbone, the fatty acid chain attached to each molecule is fundamentally different — and that difference drives nearly every performance distinction between them.
Span 20 is esterified with lauric acid (C12:0), a medium-chain saturated fatty acid. Span 80, by contrast, uses oleic acid (C18:1), a long-chain monounsaturated fatty acid containing one cis double bond. This single structural difference has cascading effects on molecular geometry, polarity, and chemical stability.
The shorter, straight chain of Span 20 yields a more compact, relatively polar molecule, while Span 80's long, kinked oleic chain creates a bulkier, more lipophilic structure. This is directly reflected in their respective HLB (Hydrophilic-Lipophilic Balance) values: 8.6 for Span 20 and 4.3 for Span 80.
| Property | Span 20 | Span 80 |
|---|---|---|
| Chemical name | Sorbitan monolaurate | Sorbitan monooleate |
| Fatty acid | Lauric acid (C12:0, saturated) | Oleic acid (C18:1, unsaturated) |
| HLB value | 8.6 | 4.3 |
| Physical state (25 °C) | Amber liquid, low viscosity | Amber viscous liquid / paste |
| Water solubility | Dispersible | Insoluble, oil-dispersible |
| Oil solubility | Soluble in most oils | Highly soluble in oils |
| Oxidative stability | High (saturated chain) | Moderate (susceptible to oxidation) |
| Thermal stability | Good | Good, but degrades faster at high temps |
Both surfactants are approved under major regulatory frameworks including FDA GRAS status, EU food additive regulations (E491 for Span 20 / E494 for Span 80), and the USP/NF monograph for pharmaceutical applications. They are also widely accepted in cosmetic formulations under INCI nomenclature.
Both Span 20 and Span 80 function primarily as water-in-oil (W/O) emulsifiers, but their practical behavior differs significantly depending on the oil phase, processing conditions, and required shelf life.
As a general rule, surfactants with HLB values below 6 favor W/O emulsions, while those in the 8–12 range support oil-in-water (O/W) systems more readily. With an HLB of 4.3, Span 80 is a classic W/O emulsifier and performs strongly in non-polar, high-lipid systems. Span 20, at HLB 8.6, sits closer to the transitional zone — it can contribute to W/O emulsification but also provides better water dispersibility, making it useful in lighter formulations or as a co-emulsifier in O/W systems.
In practice, Span surfactants are rarely used alone. They are commonly blended with their ethoxylated counterparts — Tween 20 (HLB 16.7) and Tween 80 (HLB 15.0) — to achieve a target HLB for a specific emulsion system. The required HLB of the oil phase determines the ratio:
The unsaturated C18:1 chain in Span 80 introduces a point of oxidative vulnerability. Under high-temperature processing, UV exposure, or extended storage, the double bond can undergo autoxidation, leading to rancidity, color change, and potential degradation of the emulsion. Span 20's fully saturated lauric chain is inherently more stable and requires less antioxidant support in formulations with long shelf-life requirements.
Where Span 80 is preferred for its lipophilicity, formulators typically pair it with antioxidants such as BHT, tocopherol, or rosemary extract to mitigate this risk.
Both surfactants are considered low-irritancy at typical use levels (0.5–5%). Span 20's shorter, lauric acid-derived chain has some mild antimicrobial properties — a secondary benefit in certain topical products. Span 80, widely used in pharmaceutical emulsions and vaccine adjuvants, has a well-established safety record at low concentrations, though its oleic acid component has been noted to slightly enhance skin permeation of co-formulated actives — a property that can be either advantageous or a concern depending on the application.
The distinct polarity and stability profiles of Span 20 and Span 80 translate into well-defined application preferences across cosmetics, pharmaceuticals, food processing, and industrial manufacturing.
| Industry | Span 20 — Typical Uses | Span 80 — Typical Uses |
|---|---|---|
| Cosmetics | Light emulsions, toners, water-based serums, co-emulsifier in O/W creams | Rich W/O creams, sunscreens, barrier ointments, color cosmetics |
| Pharmaceuticals | Hydrophilic ointment bases, oral emulsions, tablet coatings | Injectable emulsions, vaccine adjuvants (MF59-type), topical drug delivery |
| Food | Bakery emulsification, ice cream texture stabilization, dough conditioning | Chocolate viscosity reduction, fat bloom control, margarine processing |
| Industrial | Textile processing, latex stabilization, water-based metalworking fluids | Agrochemical emulsifiable concentrates, cutting fluids, rust-preventive coatings |
Three parameters should guide surfactant selection between Span 20 and Span 80:
