If the sorbitan esters are the oldest emulsifier family still in daily use, the PEG esters are the largest: fatty acid, fatty alcohol, glyceride and castor-oil derivatives built on polyethylene glycol chains cover more formulation space than any other single chemistry. Most "modern" emulsion systems a formulator meets — the self-emulsifying glyceryl stearate pair, fragrance solubilisers in toners, pearl thickeners in shampoos, electrolyte-tolerant water-in-oil sunscreens — rest on one of them. Yet the family is also where INCI numbering confuses buyers the most, so it is worth decoding once, properly.
Decoding the PEG numbering
The number after "PEG-" is the average number of ethylene oxide (EO) units in the polyoxyethylene chain — not a percentage, not a viscosity grade. So PEG-100 Stearate (CAS 9004-99-3) carries roughly 100 EO units (average PEG molecular weight ≈ 4,500), while PEG-8 Caprylic/Capric Glycerides (CAS 85536-07-8) carries only 8. Two practical consequences:
- More EO units → higher HLB → more water-loving. The ladder runs from PEG-30 Dipolyhydroxystearate (CAS 827596-80-5) at HLB ≈ 5.5 (a W/O emulsifier) up to PEG-100 Stearate at ≈ 18.8 (a pure O/W emulsifier).
- Chain length also sets physical form. Short chains (PEG-6/8 esters) are liquids; long chains (PEG-100/150) are waxy solids that need a 70–80 °C oil phase to dissolve cleanly.
A second convention rides on top: mono- vs diesters. PEG-100 Stearate is predominantly the monoester; PEG-150 Distearate (CAS 9005-08-7) carries two stearate chains on one PEG chain, which drops water solubility and turns it into a thickener/pearliser rather than an emulsifier. And for castor-oil derivatives such as PEG-40 Hydrogenated Castor Oil (CAS 61788-85-0), the number again counts moles of EO grafted onto the triglyceride.
The HLB ladder at a glance
| Grade | CAS | HLB (approx.) | Form | Primary role |
|---|---|---|---|---|
| PEG-30 Dipolyhydroxystearate | 827596-80-5 | ~5.5 | Viscous gel/liquid | Electrolyte-tolerant W/O emulsifier |
| PEG-40 Hydrogenated Castor Oil | 61788-85-0 | ~10.5 | Paste/liquid | Fragrance & vitamin solubiliser |
| PEG-150 Pentaerythrityl Tetrastearate | 130249-48-8 | ~12 | Waxy solid | Thickener for surfactant systems |
| PEG-7 Glyceryl Cocoate | 66105-29-1 | ~13 | Liquid | Mild solubiliser, pearliser, refatting agent |
| PEG-150 Distearate | 9005-08-7 | ~18 | Waxy solid | Pearl thickener for shampoos/cleansers |
| PEG-100 Stearate | 9004-99-3 | ~18.8 | Waxy solid | O/W emulsifier (self-emulsifying pair) |
Below the ladder sits a separate, fully oil-soluble group — PPG-15 Stearyl Ether (CAS 25231-21-4) and the PEG/PPG copolymers — used not to emulsify but to couple water-sensitive actives (aluminium salts, alcohol) into the oil phase of antiperspirants and toners.
The self-emulsifying pair: glyceryl stearate + PEG-100 stearate
The most requested emulsifier system in cosmetics is not one ingredient but a ratio. Glyceryl Stearate (CAS 31566-31-1) supplies the lipophilic, film-forming half; PEG-100 Stearate supplies the hydrophilic anchor. Blended at roughly 3 : 1 (GMS : PEG-100 S) at a total loading of 2.5–5%, the pair emulsifies classic O/W lotions and creams with a glossy, white, short-flow rheology that ionic emulsifiers still cannot copy. Key practice points:
- Dissolve both fully in the 75–80 °C oil phase; the PEG-100 fraction is the slow one and incomplete melting shows up as graininess after two weeks.
- At higher GMS:PEG ratios (4–5 : 1) the system trends to W/O consistency and richer body; at 2 : 1 it trends to thin, milk-like O/W lotions.
- One-drum alternatives exist and behave nearly identically: Cetearyl Alcohol (and) PEG-20 Stearate (CAS 67762-27-0; 9004-99-3) for hot-process lotions, and PEG-100 Glyceryl Stearate (CAS 9004-99-3) when the customer wants a single combined INCI.
- Expect pH 4.5–8 tolerance; the pair is nonionic and does not fight carbomers or electrolytes, but it does not stabilise 40%+ oil phases alone — pair it with a polymeric thickener.
Thickeners: the PEG-150 family
Two grades do most of the thickening work in surfactant systems. PEG-150 Distearate at 0.5–2% raises the viscosity of shampoos, shower gels and facial cleansers and — above roughly 1% in the presence of fatty acids and alkaline soap formed in situ — produces the classic pearl shine. It is waxy and needs 75–80 °C with vigorous stirring; add it early, not as a cool-down sprinkle. PEG-150 Pentaerythrityl Tetrastearate (CAS 130249-48-8), normally dosed 0.5–1.5% together with a small fraction of PEG-6 caprate, thickens without pearl effect and is the standard choice for clear gels, transparent cleansers and alcohol-containing toners where distearate would haze. Both are nonionic: viscosity is indifferent to pH and survives high salt loads that collapse carbomer gels.
Solubilisers: PEG-40 hydrogenated castor oil and friends
Fragrance, essential oils, vitamins A/E and salicylic acid will not dissolve in a water phase — they must be solubilised into micelles, and PEG-40 Hydrogenated Castor Oil is the workhorse. Practical ratios: 1 : 1 to 2 : 1 solubiliser : fragrance for typical fine fragrances in hydroalcoholic systems; up to 3 : 1 for heavy terpene loads (citrus oils) in straight aqueous toners; 2–5% of the blend carries 1% of an oil-soluble vitamin. Clarity must be checked at both 4 °C and 45 °C, because micellar systems haze on chilling. Two supporting grades round out the shelf: PEG-7 Glyceryl Cocoate (CAS 66105-29-1) is a milder, refatting solubiliser used at 1–3% in shampoos and body washes to cut the degreasing feel of surfactant bases while adding pearlescence; PEG-80 Sorbitan Laurate (CAS 9005-64-5) is the high-foaming solubiliser of syndet bar and bubble-bath formulations. For buyers who prefer a finished blend, Cocoeth-7 (and) PPG-1-PEG-9 Lauryl Glycol Ether (and) PEG-40 HCO (CAS 61791-13-7; 154248-98-3; 61788-85-0) is a one-drum solubiliser tuned for perfume oils in aqueous systems.
The W/O workhorse: PEG-30 dipolyhydroxystearate
Classical W/O emulsifiers (sorbitan oleate and friends) fail in two modern situations: high electrolyte systems (magnesium sulfate, aluminium chlorohydrate, mineral sunscreens above 20%) and low-viscosity sprayable W/O formulas. PEG-30 Dipolyhydroxystearate was built for exactly this: dosed at 1.5–3% it stabilises W/O systems that tolerate up to ~30% electrolyte, which is why it dominates antiperspirant sticks, deodorant creams and high-SPF W/O sunscreens. Two ready-made blends on our shelf extend it further: PEG-30 DPHS (and) Sorbitan Sesquioleate (CAS 827596-80-5; 8007-43-0) for traditional skin-feel sun care, and PEG-30 DPHS (and) Polyglyceryl-3 Diisostearate (CAS 827596-80-5; 66082-42-6) for PEG-labelled-clean and natural-positioned formulas. Process note: it is sold as a gel in ester oil — warm to 50–60 °C before weighing for accurate dosing, and add the water phase slowly under moderate shear to keep the droplet distribution tight.
Specialty couplers and bath-oil solubilisers
Two further niches complete the family. PPG-15 Stearyl Ether at 2–10% is the standard oil-phase coupling agent in antiperspirant sticks: it dissolves aluminium chlorohydrate powders cleanly, adjusts stick hardness, and leaves a dry, non-greasy glide. PEG-8 Caprylic/Capric Glycerides (CAS 85536-07-8) (and its shorter-chain sibling PEG-6 Caprylic/Capric Glycerides (CAS 308067-11-0)) are self-solubilising emollients used at 5–20% in soaking bath oils and two-phase body oils — they let the oil micro-emulsify into the bath water instead of floating as a ring. For butter-type textures, PEG-75 Shea Butter Glycerides water-disperses shea lipids into rinse-off masks and conditioner bases.
What to demand on the COA
- Acid value — ≤ 4–6 mg KOH/g for most grades. A high value means hydrolysed ester: it soaps the formula, shifts pH and can sting on skin.
- Saponification value — confirms true ester content and catches substitution with cheaper nonionic blends.
- Hydroxyl value — tracks residual free PEG; together with the saponification value it pins down the monoester/diester ratio, which is the real HLB driver.
- 1,4-dioxane (measured, ppm) — the headline ethoxylation audit. Demand the measured per-lot figure, not a compliance statement; reputable producers quote single-digit ppm.
- Free EO and oxirane residuals — same logic, relevant for EU customers in particular.
- Water content (Karl Fischer) — ≤ 1% for waxy grades; water causes haze in finished clear systems and hydrolysis on storage.
- Congealing/drop point and colour (Gardner) — waxy grades (PEG-100/150) must melt into the oil phase cleanly; a drifting colour usually means oxidised feedstock fatty acid.
- Heavy metals — Pb ≤ 10 ppm, As ≤ 2 ppm for cosmetic grades.
Selection checklist
Six questions settle most briefs. O/W emulsion? Start with the glyceryl stearate + PEG-100 stearate pair at 3 : 1, 2.5–5% total. Thickening a cleanser or shampoo? PEG-150 distearate for pearl, PEG-150 pentaerythrityl tetrastearate for clarity. Solubilising fragrance or actives in water? PEG-40 HCO first, PEG-7 glyceryl cocoate for a milder feel. High electrolyte W/O? PEG-30 dipolyhydroxystearate at 1.5–3%. Antiperspirant stick? PPG-15 stearyl ether in the oil phase. EU customer sensitive to ethoxylation? Keep the sorbitan and polyglyceryl ester families in the conversation — but note that even "PEG-free" claims rarely survive a full audit of a modern formulation; measured 1,4-dioxane control is the honest answer.
Shanghai Better Chemical supplies the full PEG ester toolkit — PEG-100 Stearate (CAS 9004-99-3), PEG-40 Hydrogenated Castor Oil (CAS 61788-85-0), PEG-150 Distearate (CAS 9005-08-7), PEG-150 Pentaerythrityl Tetrastearate (CAS 130249-48-8), PEG-30 Dipolyhydroxystearate (CAS 827596-80-5), PEG-7 Glyceryl Cocoate (CAS 66105-29-1), PEG-8 Caprylic/Capric Glycerides (CAS 85536-07-8), PEG-80 Sorbitan Laurate (CAS 9005-64-5), PPG-15 Stearyl Ether (CAS 25231-21-4) and ready-made blends such as Cetearyl Alcohol (and) PEG-20 Stearate and PEG-30 DPHS (and) PG-3 Diisostearate — with per-lot COA covering acid value, saponification value, hydroxyl value and measured 1,4-dioxane figures. TDS/MSDS and pre-shipment samples are available for bench validation; tell us your emulsion type and target system and we will propose grades, ratios and current pricing.