For formulation engineers, emulsion stability depends on getting three things right: the HLB match, the solubility profile, and the rheological behavior of your surfactant. This guide covers the calculation methodology and physical property data you need — the how rather than the what.
For help deciding which Span to choose for a specific application (bakery, cosmetics, agrochemicals, etc.), see our Selection & Applications Guide. For sourcing, browse the Span Series product page.
1. The HLB System: Theory and Calculation
The Hydrophilic-Lipophilic Balance (HLB) scale (0–20) predicts whether a surfactant will stabilize a Water-in-Oil (W/O) or Oil-in-Water (O/W) emulsion.
Span HLB Values
Sorbitan esters are lipophilic, occupying the low end of the scale:
| Product | Chemical Name | HLB | Water Dispersibility |
|---|---|---|---|
| Span 85 | Sorbitan Trioleate | 1.8 | Insoluble |
| Span 65 | Sorbitan Tristearate | 2.1 | Insoluble |
| Span 80 | Sorbitan Monooleate | 4.3 | Insoluble (dispersible with shear) |
| Span 60 | Sorbitan Monostearate | 4.7 | Dispersible in hot water |
| Span 40 | Sorbitan Monopalmitate | 6.7 | Dispersible in hot water |
| Span 20 | Sorbitan Monolaurate | 8.6 | Dispersible (cloudy solution) |
For detailed physical and chemical data on individual Span grades, see the Sorbitan Monostearate (E491) Technical Guide and the Span 80 Technical Guide.
The Required HLB Concept
Every oil phase has a required HLB (rHLB) — the HLB value at which the most stable emulsion forms. Common values:
| Oil Phase | rHLB (W/O) | rHLB (O/W) |
|---|---|---|
| Soybean oil | 6 | 12 |
| Mineral oil (light) | 5 | 10.5 |
| Isopropyl myristate | 5–6 | 11.5 |
| Beeswax | 5 | 12 |
| Coconut oil | — | 8 |
| Silicone oil (dimethicone) | 5 | 9 |
The Blending Formula
A single surfactant rarely hits the target rHLB. The standard approach blends a low-HLB Span with a high-HLB Tween (Polysorbate):
% Surfactant A = (rHLB − HLB_B) / (HLB_A − HLB_B) × 100
Where Surfactant A is the high-HLB surfactant and Surfactant B is the low-HLB one.
For a complete Span-Tween pairing reference, see the Span & Tween Formulators Guide.
Worked Example 1: Mineral Oil W/O Emulsion
Goal: Emulsify light mineral oil (rHLB = 5) using Span 80 (HLB 4.3) and Tween 80 (HLB 15.0).
% Tween 80 = (5 − 4.3) / (15.0 − 4.3) × 100 = 0.7 / 10.7 × 100 = 6.5%
Result: 6.5% Tween 80 + 93.5% Span 80. The blend HLB is 5.0. Expect a stable W/O emulsion.
Worked Example 2: Soybean Oil O/W Emulsion
Goal: Emulsify soybean oil (rHLB = 12 for O/W) using Span 60 (HLB 4.7) and Tween 60 (HLB 14.9).
% Tween 60 = (12 − 4.7) / (14.9 − 4.7) × 100 = 7.3 / 10.2 × 100 = 71.6%
Result: 71.6% Tween 60 + 28.4% Span 60. The blend HLB is 12.0. Expect a stable O/W emulsion.
Worked Example 3: High-Oil System with Extreme Low HLB
Goal: Stabilize a system with >80% oil phase using Span 85 (HLB 1.8) and Tween 85 (HLB 11.0). Target rHLB = 4.
% Tween 85 = (4 − 1.8) / (11.0 − 1.8) × 100 = 2.2 / 9.2 × 100 = 23.9%
Result: 23.9% Tween 85 + 76.1% Span 85. This ultra-low-HLB blend is suitable for oil-phase defoamers and extreme W/O systems.
2. Solubility Profiles
HLB tells you about emulsion type, but solubility determines how the surfactant behaves during processing.
In Oils and Organic Solvents
| Product | Mineral Oil | Vegetable Oil | Ethanol | Isopropanol | Ethyl Acetate |
|---|---|---|---|---|---|
| Span 20 | Soluble | Soluble (hot) | Soluble | Soluble | Soluble |
| Span 60 | Dispersible (hot) | Soluble (hot) | Partial | Partial | Soluble (hot) |
| Span 80 | Soluble | Soluble | Soluble | Soluble | Soluble |
| Span 85 | Soluble | Soluble | Soluble | Soluble | Soluble |
- Span 80 and 85 are the most oil-soluble members. Their oleic acid chain (C18:1, unsaturated) keeps them fluid and miscible in non-polar solvents at room temperature.
- Span 60 requires heat to dissolve in oils because its saturated C18 chain crystallizes at ambient temperature.
In Water
All Span esters are water-insoluble in the strict sense — they disperse, not dissolve:
- Span 20: Forms cloudy, milky dispersions due to its shorter C12 chain. The closest the Span family gets to water solubility.
- Span 40/60: Require hot water and shear to disperse. Upon cooling, Span 60 re-crystallizes, which can be used to build structured networks in creams.
- Span 80/85: Practically non-dispersible in water alone. Require a co-surfactant (Tween) or high-shear mixing.
Solubility Rule of Thumb
Shorter fatty acid chain + unsaturation = better solubility in both oil and polar solvents.
Longer saturated chain = requires heat, but provides better structure.
3. Viscosity and Rheology
The physical state of a Sorbitan Ester directly affects the texture and processability of your formulation. For pour point and melting point data across the full Span-Tween range, see the Surfactant Pour Point & Melting Point Guide.
Liquid Spans (20, 80, 85)
| Product | Viscosity at 25°C (mPa·s) | Pour Point (°C) | Behavior |
|---|---|---|---|
| Span 20 | 3,000–5,000 | ~15 | Pumpable at room temp; slight haziness possible |
| Span 80 | 1,000–2,000 | ~5 | Lowest viscosity Span; stays fluid to near-freezing |
| Span 85 | 200–400 | ~–10 | Very low viscosity; near-Newtonian flow |
- Span 80 is the preferred choice when a low-viscosity, pumpable W/O emulsifier is needed. The unsaturated oleic chain prevents crystallization.
- Span 85 is the lowest-viscosity option — suitable for systems requiring minimal surfactant contribution to overall viscosity.
Solid Spans (40, 60, 65)
| Product | Melting Point (°C) | Physical Form | Rheological Role |
|---|---|---|---|
| Span 40 | 46–52 | Cream paste / soft solid | Structure builder, bodying agent |
| Span 60 | 52–57 | Tan beads / flakes | Crystallization network; aeration stabilizer |
| Span 65 | 53–58 | Tan beads / powder | Crystal modifier; hardest solid Span |
- Span 60 is the most important solid Span for rheology. When melted into the oil phase and cooled, it forms a 3D crystalline network that thickens creams, stabilizes air bubbles in whipped products, and prevents oil separation.
- Span 65 (triester) creates denser, more rigid crystal structures than Span 60 (monoester) — useful for chocolate anti-bloom and compressed powder binders.
Temperature Sensitivity in Processing
Solid Spans must be heated above their melting point during emulsification. Key considerations:
- Pre-melt Span 60/65 in the oil phase at 60–70°C (10–15°C above melting point).
- Maintain the water phase at the same temperature to prevent thermal shock during mixing.
- Controlled cooling rate determines crystal size and final texture — rapid cooling yields fine crystals (smooth texture); slow cooling yields coarse crystals (grainy texture).
4. Span-Tween Pairing: Choosing the Right Partner
Once you’ve calculated the required Span:Tween ratio (using the formula in Section 1), select the correct Tween counterpart:
| Span | Fatty Acid | Best Tween Partner | Reason |
|---|---|---|---|
| Span 20 (C12) | Lauric | Tween 20 | Same C12 chain; HLB 16.7 |
| Span 40 (C16) | Palmitic | Tween 40 | Same C16 chain; HLB 15.6 |
| Span 60 (C18) | Stearic | Tween 60 | Same C18 chain; HLB 14.9 |
| Span 80 (C18:1) | Oleic | Tween 80 | Same C18:1 chain; HLB 15.0 |
| Span 85 (C18:1×3) | Oleic | Tween 85 | Same C18:1 chain; HLB 11.0 |
Matching fatty acid chain lengths between Span and Tween maximizes interfacial packing density and emulsion stability. Mismatched chains (e.g., Span 60 + Tween 80) still work but produce less ordered interfacial films.
For detailed pairing methodology and worked recipes, see the Span & Tween Formulators Guide.
Summary
Formulating with Sorbitan Esters comes down to three calculations:
- HLB: Use the blending formula to hit your oil phase’s rHLB exactly.
- Solubility: Match the Span’s solubility profile to your solvent system and processing temperature.
- Rheology: Choose liquid Span (80/85) for low-viscosity products, solid Span (60/65) for structured creams and aeration.
For product recommendations by application (food, cosmetics, industrial), consult the Selection & Applications Guide. For technical data sheets or formulation support, contact FoodEmul.com.
Browse our Span Series: Sorbitan Monostearate (Span 60), Sorbitan Monooleate (Span 80), and Sorbitan Trioleate (Span 85).
