Every emulsifier family has a classic pairing, and this is the oldest one still in production: the sorbitan fatty acid esters — sold under the Span shorthand — for water-in-oil systems, and their ethoxylated counterparts, the polysorbates (Tween shorthand), for oil-in-water. The chemistry dates to the 1940s, yet walk into any sunscreen, foundation or cold-cream plant today and you will find both in use. The reason is simple: the pair covers the HLB scale from 1.8 to 16.7 with one coherent chemistry, tolerates high electrolyte and pigment loads, is cheap, and is approved for food use in both ester families. When a formulator needs a W/O system that survives 20% zinc oxide or a sebum-rich summer, this is still where they start.
Decoding the numbering
Both series are built on sorbitan — dehydrated sorbitol, a five-membered anhydrosorbitol ring — esterified with one fatty acid (the sorbitan esters) or ethoxylated with roughly 20 moles of ethylene oxide after esterification (the polysorbates). The number in the trade name refers to the fatty acid, and it is consistent across both series:
- 20 = laurate (C12) — Sorbitan Laurate (CAS 1338-39-2) and Polysorbate 20 (CAS 9005-64-5)
- 40 = palmitate (C16) — Sorbitan Palmitate (CAS 26266-57-9) and Polysorbate 40 (CAS 9005-66-7)
- 60 = stearate (C18) — Sorbitan Stearate (CAS 1338-41-6) and Polysorbate 60 (CAS 9005-67-8)
- 80 = oleate (C18:1) — Sorbitan Oleate (CAS 1338-43-8) and Polysorbate 80 (CAS 9005-65-6)
- 85 = trioleate (three C18:1 esters) — Sorbitan Trioleate (CAS 26266-58-4) and Polysorbate 85 (CAS 9005-70-3)
Two grades sit outside the numbered scheme: Sorbitan Sesquioleate (CAS 8007-43-0), the 1.5-oleate classic of W/O sun care, and Sorbitan Isostearate (CAS 71902-01-7), the branched-chain liquid variant preferred in colour cosmetics for its low melting point and better pigment wetting.
The HLB ladder
| Grade | CAS | HLB | Form | Primary role |
|---|---|---|---|---|
| Sorbitan Trioleate (Span 85) | 26266-58-4 | 1.8 | Viscous liquid | Extreme W/O, anhydrous balms |
| Sorbitan Oleate (Span 80) | 1338-43-8 | 4.3 | Viscous liquid | W/O primary emulsifier |
| Sorbitan Sesquioleate | 8007-43-0 | ~4 | Liquid | W/O sun care workhorse |
| Sorbitan Isostearate | 71902-01-7 | ~4.5 | Liquid | W/O creams, pigment wetting |
| Sorbitan Stearate (Span 60) | 1338-41-6 | 4.7 | Waxy solid | W/O creams, consistency |
| Sorbitan Palmitate (Span 40) | 26266-57-9 | 6.7 | Waxy solid | Intermediate HLB, co-emulsifier |
| Sorbitan Laurate (Span 20) | 1338-39-2 | 8.6 | Paste | Mild O/W co-emulsifier |
| Polysorbate 85 | 9005-70-3 | 11.0 | Liquid | Vitamin/oil solubilisation |
| Polysorbate 60 | 9005-67-8 | 14.9 | Paste | O/W emulsifier, food E435 |
| Polysorbate 80 | 9005-65-6 | 15.0 | Liquid | O/W emulsifier, solubiliser E433 |
| Polysorbate 40 | 9005-66-7 | 15.6 | Paste | O/W, fragrance solubilisation |
| Polysorbate 20 | 9005-64-5 | 16.7 | Liquid | Fragrance/essential-oil solubiliser E432 |
Read the ladder from bottom to top and the logic of the family is visible: esterification degree and chain saturation pull HLB down, ethoxylation pushes it up. Within the sorbitan esters themselves, the range 1.8–8.6 is deliberately oil-soluble — they are W/O tools first, with only the laurate reaching into mild O/W co-emulsifier territory.
Pairing arithmetic: hitting a target HLB
The classic use of the pair is blending a sorbitan ester with its polysorbate partner to match the "required HLB" of the oil phase. The arithmetic is linear on the weight fraction:
Example. An emollient phase of caprylic/capric triglyceride and jojoba-type esters has a required HLB of roughly 10. Using Sorbitan Oleate (4.3) and Polysorbate 80 (15.0): the fraction of Polysorbate 80 = (10 − 4.3) / (15.0 − 4.3) = 5.7 / 10.7 ≈ 0.53. So a 53 : 47 blend of Polysorbate 80 : Sorbitan Oleate at a total loading of 3–5% is the starting experiment, then adjusted up or down by 0.5 HLB units until the emulsion is stable through three freeze–thaw cycles. In practice the sorbitan ester usually carries 30–50% of the emulsifier blend even in O/W systems, because it strengthens the interfacial film and improves the yield value of the cream.
Three cautions with this method. First, the required HLB of an oil is a range, not a constant — it shifts with the other ingredients, so treat the calculation as a starting point for the bench, not a final answer. Second, nonionic blends built this way are salt-tolerant but weak against high shea or wax loads; add a fatty alcohol or a second lipophilic co-emulsifier to carry the structure. Third, HLB says nothing about droplet size or skin feel — a system can be HLB-correct and still coarse — so pair the arithmetic with a microscopy or centrifuge check.
Where each half of the family works
| Application | Recommended system | Use level | Why it works |
|---|---|---|---|
| W/O sunscreen (SPF 30–50+) | Sorbitan Sesquioleate or Sorbitan Isostearate 2–4% + Sorbitan Trioleate 0.5–1% | 3–5% total | Both grades tolerate 20%+ mineral UV filters; the trioleate locks the interfacial film against coalescence |
| W/O day creams and cold creams | Sorbitan Oleate 2–3% or Sorbitan Stearate 3–5% + beeswax/lanolin structure | 3–6% total | Stearate version gives body; oleate version stays fluid and lower-viscosity |
| Foundations and colour cosmetics | Sorbitan Isostearate 2–3% with Sorbitan Trioleate 0.5–1% to disperse pigments | 2–4% total | The branched isostearate wets pigments faster and keeps the formula liquid at room temperature |
| O/W lotions (classic, non-PEG-labelled) | Sorbitan Laurate 1–2% + Polysorbate 20 or 60 2–3%, plus fatty alcohol | 3–5% total | One of the mildest O/W systems available; the laurate halves the irritancy vs. stronger ethoxylates |
| Fragrance and essential-oil solubilisation | Polysorbate 20 4–8% or Polysorbate 80 3–6% per 1% fragrance load | see text | Clear micro-emulsions in water; Polysorbate 80 carries heavier terpene loads better |
| Vitamin and oil-soluble actives | Polysorbate 85 2–5% in oil-based serums, or Polysorbate 80 in O/W emulsions | 2–5% | Keeps tocopherol and carotenoid loads evenly dispersed |
Polysorbate-specific quality questions
Because the polysorbate half of the family is made with ethylene oxide, procurement needs two extra checks that do not apply to the sorbitan esters themselves. 1,4-dioxane is the headline one — ask for the measured value on the COA, not just a statement of compliance; reputable Chinese and Western producers now routinely quote single-digit ppm. EO residuals and oxirane follow the same logic. For food or oral-care use, confirm the relevant E-number specification (E432–E436) and, where the customer is European, the EU impurity limits for polysorbates. On the sorbitan ester side, the audits are simpler but no less important: the acid value and the colour tell you how the fatty acid feedstock was handled.
What to demand on the COA
- Acid value — the primary freshness indicator; ≤ 4–6 mg KOH/g depending on grade. A high value means hydrolysed ester, which will soap the formula and sting on skin.
- Saponification value — confirms ester content and catches blending with cheaper esters.
- Hydroxyl value — for the sorbitan esters, tracks the free-hydroxyl content and hence true HLB position.
- Water content (Karl Fischer) — ≤ 1–2% for waxy grades; excess water causes cloudiness in finished W/O systems.
- Colour (Gardner/APHA) — a darkening lot usually means oxidised oleate; reject anything that drifts more than 2 Gardner units from the reference.
- HLB (measured, not catalogue) — varies with ester distribution; ask for the supplier's own titration.
- 1,4-dioxane and EO residuals (polysorbates only) — demand measured ppm values, not a pass/fail stamp.
- Heavy metals — Pb ≤ 10 ppm, As ≤ 2 ppm for cosmetic grades; tighter for food.
Selection checklist
Four questions settle most briefs. W/O or O/W? W/O starts at Sorbitan Oleate, Sesquioleate or Isostearate; O/W starts at a polysorbate with a sorbitan ester as co-emulsifier. High pigment or electrolyte load? Stay fully in the sorbitan ester half — the nonionic interface survives mineral filters and salts better than any ionic system. What is the product's temperature history? Waxy grades (stearate, palmitate) need a 75–80 °C oil phase to dissolve properly; if the process is cold, switch to the liquid oleate or isostearate. Food or oral-care contact? Both families have food-grade options, but the polysorbate half carries the extra 1,4-dioxane audit — verify it per lot, not per year.
Shanghai Better Chemical supplies the complete Span/polysorbate toolkit — Sorbitan Laurate (CAS 1338-39-2), Sorbitan Palmitate (CAS 26266-57-9), Sorbitan Stearate (CAS 1338-41-6), Sorbitan Sesquioleate (CAS 8007-43-0), Sorbitan Isostearate (CAS 71902-01-7), Sorbitan Oleate (CAS 1338-43-8), Sorbitan Trioleate (CAS 26266-58-4), Polysorbate 20 (CAS 9005-64-5), Polysorbate 40 (CAS 9005-66-7), Polysorbate 60 (CAS 9005-67-8), Polysorbate 80 (CAS 9005-65-6) and Polysorbate 85 (CAS 9005-70-3) — with per-lot COA covering acid value, saponification value, water content and, for the polysorbates, measured 1,4-dioxane figures. TDS/MSDS and pre-shipment samples are available for bench validation; tell us your emulsion type, oil-phase composition and target HLB, and we will propose the blend ratio and quote current pricing.