Formulators reach for HLB when they choose a nonionic surfactant, and for emulsifier selection that is the right instinct. For wetting, cleaning and foam control it is the wrong one. Once a polyether has to work at 50-70 degrees C - bottle washing, machine dishwash, hard-surface cleaning, textile pretreatment - the property that predicts behaviour is the cloud point, and the cloud point is governed by how much propylene oxide sits in the chain rather than by the HLB number.
What the cloud point actually tells you
Ethylene-oxide surfactants show reverse solubility in water: heating them eventually breaks the hydrogen bonding that keeps them dissolved, and the solution turns cloudy. That temperature is the cloud point. Below it, the surfactant is fully soluble, sits at the interface and stabilises foam. Above it, the molecule dehydrates and separates into a surfactant-rich coacervate that no longer supports a lamella - so foam collapses. A PO-rich ether simply does the same thing at a much lower temperature, because the methyl side group on each propylene oxide unit is hydrophobic and disrupts the water structure earlier.
Read it as a design rule: if you want low foam at 60 degrees C, buy a surfactant whose cloud point is well below 60 degrees C. PPG-3 caprylyl ether, with a cloud point under 20 degrees C in 1% aqueous solution, is that decision already made for you. If you want a wetter that stays soluble and low-foaming through a cold rinse, the same molecule still works - it is simply above its cloud point over most of the process.
The PO-block toolbox
| Product | CAS | Key specification | What it does | Typical use level |
|---|---|---|---|---|
| PPG-3 Caprylyl Ether | 29117-02-0 | Hydroxyl value 170-190; refractive index 1.440-1.450; HLB about 8-10; cloud point under 20 degrees C (1% in water) | Low-foam wetter and spreading aid; silicone-free conditioning; dissolves UV filters and lipophilic actives | 1-10% |
| PPG-3 Hydrogenated Castor Oil | 111870-68-9 | HLB about 8-10; iodine value 5 or less; density 0.948 g/cm3; pH 5.0-8.0 (1% solution); liquid at room temperature | Co-emulsifier with emollient character; saturated, cold-processable, no ethoxylation route | 1-5% co-emulsifier; 2-20% in sticks |
| PEG/PPG-17/4 Dimethyl Ether | 61419-46-3 | Water-soluble ether; low odour | Solubiliser and solvent for poorly soluble actives and fragrances | as required |
| PEG/PPG-17/6 Copolymer | 9003-11-6 | Hydroxyl value 85-110; HLB about 12; pH 5.0-7.0 (1% solution) | Solubiliser, viscosity reducer and anti-foam in surfactant systems | 1-10% |
| PEG-10 Dimethicone | 68937-54-2 | Silicone-polyether hybrid | Emulsifier that bridges a silicone oil phase into water | 1-5% |
The silicone-replacement trick most people get backwards
PPG-3 caprylyl ether is sold as a silicone alternative for hair care, and the mechanism is worth understanding before you swap it in. Dimethicone smooths the cuticle extremely well but suppresses foam, so high loadings in a clear shampoo cost you lather. A short PO ether smooths the cuticle about as well - suppliers report cuticle closure comparable to dimethicone - while remaining surface-active enough to stabilise the foam film instead of breaking it. In a clear shampoo the practical result is that you can condition without giving up foam, which is the opposite of the trade-off silicone forces on you. It also means the same molecule is a wetter in an industrial cleaner and a conditioner in a shampoo: same cloud point physics, different pH and different substrate.
Why PPG-3 hydrogenated castor oil is not just cheaper PEG-40
- HLB position. PEG-40 hydrogenated castor oil sits at HLB 13-15 and works as a high-HLB solubiliser. PPG-3 hydrogenated castor oil sits at about 8-10, which is a co-emulsifier position - better for low-water and anhydrous systems, wrong for solubilising a fragrance into water.
- Impurity profile. Propoxylation does not produce 1,4-dioxane or residual ethylene oxide, the two impurities that retail-restricted lists keep flagging on ethoxylated raw materials. For a clean-beauty brief that alone can settle the choice.
- Oxidative stability. The methyl side group on the PO backbone sterically shields the ether linkage, which gives it more resistance to oxidation than a PEG backbone - useful when the formula carries retinol, tocopherol or an unsaturated oil that would otherwise be pushed toward peroxide formation.
- Handling. It is a pumpable liquid at room temperature, so it can be charged cold; PEG-40 and PEG-60 grades are pastes that have to be melted at 40-50 degrees C, which rules out cold processing for heat-labile actives.
- Saturation. Hydrogenated castor oil carries an iodine value of 5 or less against roughly 82-90 for native castor oil, so it brings the pigment wetting and gloss of castor oil without the rancidity risk.
Where each one earns its place
- Home care: low-foam rinse aids and machine dishwash at 55-70 degrees C - PO ethers with a cloud point below the wash temperature; PEG/PPG-17/6 copolymer as the foam-control partner in a surfactant-heavy system.
- Industrial and institutional cleaning: hard-surface and metal cleaning where a wetter must not generate a foam blanket - PPG-3 caprylyl ether at 1-5%.
- Textile and leather processing: penetrating and levelling agents; note that PPG-3 hydrogenated castor oil also disperses calcium soaps, which is why it appears in fibre finishes.
- Personal care: silicone-free conditioning and dry-touch emollience; solubilising lipophilic actives.
- Anhydrous colour: PPG-3 hydrogenated castor oil at 2-20% as the saturated castor replacement.
If you are still working from the ethoxylate side of the map, our ethoxylated fatty alcohol guide covers EO number selection and the point at which a cloud point becomes a specification rather than a curiosity.
What belongs on the purchase order
- Cloud point with the concentration and medium stated: 1% in water and 10% in butyl diglycol give completely different numbers for the same product.
- Hydroxyl value as the identity and batch-consistency check - 170-190 for PPG-3 caprylyl ether, 85-110 for PEG/PPG-17/6 copolymer.
- HLB quoted as nominal, with the ethylene oxide and propylene oxide mole ratios printed separately. HLB alone does not fix a polyether.
- pH of a 1% solution (5.0-8.0 for the castor derivative) and water content.
- Residual ethylene oxide and 1,4-dioxane declaration where the grade is ethoxylated, and a statement that a propoxylated grade is free of both.
Quick selection
- Wetter that must not foam, hot process: PPG-3 caprylyl ether.
- Co-emulsifier for a low-water or anhydrous system, no ethoxylation route, cold process: PPG-3 hydrogenated castor oil.
- Solubiliser for a lipophilic active in a clear aqueous system: PEG/PPG-17/4 dimethyl ether, with PEG/PPG-17/6 copolymer where foam also has to be controlled.
- Silicone-free conditioning without losing lather: PPG-3 caprylyl ether at 1-3% in a clear shampoo.
Shanghai Better Chemical supplies the propoxylated set - PPG-3 Caprylyl Ether (CAS 29117-02-0), PPG-3 Hydrogenated Castor Oil (CAS 111870-68-9), PEG/PPG-17/4 Dimethyl Ether (CAS 61419-46-3), PEG/PPG-17/6 Copolymer (CAS 9003-11-6) and PEG-10 Dimethicone (CAS 68937-54-2) - with cloud point, hydroxyl value, EO/PO ratio and residue declarations on the certificate of analysis. Tell us the process temperature, the foam requirement and the substrate and we will quote the ether that fits.