What are Nonyl Phenol Ethoxylates?
Nonyl phenol ethoxylates are nonionic surfactants produced by reacting nonyl phenol with ethylene oxide (EO) under alkaline catalysis, mole by mole, inside a pressurised reactor. The branched C9 alkyl chain on the phenol ring supplies the oil-loving half of the molecule, while the polyoxyethylene chain built during ethoxylation supplies the water-loving half:
C9H19–C6H4–OH + n(C2H4O) → C9H19–C6H4–O–(C2H4O)n–H
(Nonyl phenol reacting with n moles of ethylene oxide; CAS 9016-45-9)
The "n" in NP-n is the average number of EO moles added per mole of nonyl phenol, and it is the single variable that governs almost everything about the finished surfactant — HLB, cloud point, water solubility, even physical form. At the low end (NP-2 to NP-6) the product is an oily, almost water-insoluble liquid; by NP-15 and above it's a waxy paste or solid that disperses freely in water. NP-9 and NP-10 sit squarely in the middle of that range, which is exactly why they're the two grades most commonly specified for general-purpose emulsification, wetting and detergency work, and why they get compared so often.
What is NP-9?
NP-9 (9 moles EO, manufactured by Rishit Polysurf as PLXOL N 900) is the more lipophilic of the two grades, with an HLB of 12.9. At 25°C it's a pale yellow liquid, clear to slightly hazy, with a hydroxyl value of 85–100 mg KOH/g, moisture ≤0.5%, pH (1% aqueous) of 5.5–7.5, and a cloud point of 50–55°C.
That cloud point matters more than the number suggests. Below roughly 50°C, NP-9 stays fully dispersed in water; push the bath hotter and the surfactant begins to come out of solution. In practice, this makes NP-9 the workhorse grade for moderate-temperature aqueous systems — alkaline metal degreasers, ambient-temperature textile scouring, and as a primary emulsifier in emulsion-polymerisation recipes — where its slightly stronger oil affinity gives it an edge in lifting greases and stabilising non-polar monomers.
What is NP-10?
NP-10 (10 moles EO, PLXOL N 1000) carries one more mole of ethylene oxide than NP-9, which nudges HLB up to 13.3 and lifts the cloud point to 52–58°C. The hydroxyl value drops slightly to 76–92 mg KOH/g, reflecting the longer, more hydrophilic polyoxyethylene chain attached to the same C9 phenol backbone. At room temperature it's a clean pale yellow liquid, with moisture and pH specifications matching NP-9.
The practical effect of that small shift is a few extra degrees of thermal headroom and marginally better cold-water dispersibility. Formulators reach for NP-10 when a process runs a touch hotter than NP-9 can comfortably tolerate — high-temperature scouring and dyeing baths, for example — or when a formulation needs slightly more hydrophilic character to balance a low-HLB co-surfactant in a blend.
NP-9 vs NP-10 Comparison Table
| Parameter | NP-9 (PLXOL N 900) | NP-10 (PLXOL N 1000) |
|---|---|---|
| EO Moles | 9 | 10 |
| HLB Value | 12.9 | 13.3 |
| Appearance (25°C) | Pale yellow, clear to slightly hazy liquid | Pale yellow liquid |
| Moisture | ≤ 0.5% | ≤ 0.5% |
| pH (1% aqueous) | 5.5–7.5 | 5.5–7.5 |
| Hydroxyl Value | 85–100 mg KOH/g | 76–92 mg KOH/g |
| Cloud Point (1% aq.) | 50–55°C | 52–58°C |
| Colour (APHA) | ≤ 60 | ≤ 60 |
| Surface Tension | ~31 mN/m | ~31 mN/m |
| Pour Point | −1°C | +2°C |
| CAS No. | 9016-45-9 | 9016-45-9 |
| Overall character | Slightly more lipophilic | Slightly more hydrophilic |
Both grades share the same general pH range, moisture spec and surface tension, which is exactly why they're so often discussed as a pair. The real decision usually comes down to two numbers: HLB and cloud point.
HLB Value Comparison
HLB (Hydrophilic–Lipophilic Balance) is a 0–20 scale describing how water-loving or oil-loving a nonionic surfactant is. Low values (roughly 3–6) suit water-in-oil emulsions, mid values (around 8–15) suit oil-in-water emulsification and wetting, and higher values (15 and above) lean toward detergency and solubilisation. NP-9 (12.9) and NP-10 (13.3) both land inside the oil-in-water emulsifier band, which is exactly why either grade can technically work in many of the same formulations.
The 0.4-point gap between them is small but not irrelevant. NP-9's slightly lower HLB gives it relatively more lipophilic character — useful when the oil phase being emulsified is fairly non-polar, such as mineral oils or waxes — while NP-10's marginally higher HLB gives it a small edge wherever the system needs to lean more hydrophilic, such as stabilising slightly polar oils or improving rinse-off in a wash formulation.
Because HLB is an additive property, both grades are also routinely blended with lower-mole products like NP-4 or NP-6 to dial a formulation into a precise target HLB, rather than relying on a single off-the-shelf grade. This is standard practice in agrochemical EC and emulsion-polymerisation work, where the target HLB is often a fraction outside what any single commercial grade offers on its own.
Emulsification and Wetting Performance
In practice, the HLB and cloud-point gap between NP-9 and NP-10 shows up in three places:
- Oil-cutting power: NP-9's slightly higher lipophilicity gives it marginally stronger detergency against mineral oils and machining greases, which is one reason it shows up so often in alkaline metal cleaners and degreaser formulations.
- Thermal stability: NP-10's higher cloud point (52–58°C vs. 50–55°C) provides a wider safety margin before the surfactant clouds out of solution — useful in hot scouring baths, summer storage, and high-ambient-temperature transport and warehousing.
- Water dispersibility: NP-10 disperses a little faster and more completely in cold-to-warm water, which can simplify make-up of dilute working baths on the plant floor.
Neither difference is dramatic in isolation — formulators routinely substitute one grade for the other with only minor adjustment to dosage or co-surfactant ratio. But in a tightly tuned recipe running close to its operating limits, the wrong choice is often the difference between a stable bath and one that clouds, separates or redeposits soil onto the substrate.
Applications of NP-9
- Alkaline metal cleaners and degreasers — NP-9's oil-cutting strength lifts machining oils and petroleum-based soils even in high-caustic, high-electrolyte wash formulations.
- Emulsion polymerisation — alongside NP-4 and NP-6, NP-9 is a standard nonionic emulsifier for acrylic latex, vinyl-acetate latex and SBR-type systems, prized for its electrolyte tolerance.
- Agrochemical EC formulations — used as an emulsifier and co-solvent in emulsifiable-concentrate insecticides, fungicides and herbicides, helping the active ingredient disperse cleanly at spray-tank dilution.
- Metalworking fluid formulation — functions as the primary emulsifier in soluble and semi-synthetic cutting and coolant fluids.
Applications of NP-10
- Textile wet processing — NP-10 takes over scouring and dyeing-assistant duty in baths that run a few degrees hotter than NP-9 can comfortably tolerate, reducing the risk of mid-process clouding.
- Agrochemical EC formulations — often blended alongside lower-mole grades where a marginally more hydrophilic emulsifier improves spray-tank and dilution stability.
- Paints and coatings — used as a pigment-dispersing and wetting agent in water-borne industrial paints, primers and architectural coatings.
- Industrial and institutional cleaning concentrates — suited to formulations intended for slightly warmer wash or rinse conditions than a standard NP-9-based cleaner.
How to Select the Right Grade
- Match cloud point to process temperature. Keep at least 5–10°C of margin between your maximum operating temperature and the surfactant's cloud point. If your bath runs hot, NP-10 — or a custom blend — is the safer starting point.
- Calculate your target HLB. If your system needs an HLB outside the 12.9–13.3 window, blend NP-9 or NP-10 with a lower-mole grade such as NP-4 or NP-6; HLB combines additively across a blend.
- Check your destination market. Nonylphenol and its ethoxylates are restricted under REACH Annex XVII in the EU above a 0.1% concentration threshold for most industrial and institutional uses (0.01% for textile articles). For EU-facing supply chains, ask our team about REACH-compliant alternatives such as Card Phenol Ethoxylates or Lauryl Alcohol Ethoxylates.
- Weigh cost against performance. NP-9 and NP-10 are priced closely; the deciding factor is almost always thermal margin and HLB fit rather than raw material cost.
- When in doubt, ask. Our technical team can recommend a single grade or a custom NP-9/NP-10 blend based on your oil phase, process temperature and electrolyte load.
Packaging
Both grades are manufactured at our GIDC Dholka facility under in-house quality control and supplied in 200 kg barrels or bulk ISO tank/flexi-tanker loads; smaller sample quantities can be arranged on request through our technical sales team.
Conclusion
NP-9 and NP-10 are close cousins on the nonylphenol ethoxylate ladder, separated by one mole of ethylene oxide, 0.4 HLB units, and a handful of degrees of cloud point. That gap is small enough that either grade can often substitute for the other, and large enough to matter the moment a process runs hot, an emulsion is tightly tuned, or a formulation needs to hit a precise HLB target.
Rishit Polysurf LLP manufactures both grades — along with the complete PLXOL™ range from NP-2 to NP-40 — at our ethoxylation facility in GIDC Dholka, Gujarat, with in-house testing on every batch. If you're not sure whether NP-9, NP-10 or a custom blend is right for your formulation, contact our technical sales team or call +91 83206 81017 for grade selection support, samples, TDS/MSDS and bulk pricing.
Request TDS, MSDS, Samples or Bulk Pricing
Rishit Polysurf LLP manufactures Nonyl Phenol Ethoxylates from its facility in GIDC Dholka, Gujarat. Contact our technical sales team for grade selection, TDS, MSDS, sample availability and bulk pricing. Need help selecting the right NPE grade for your formulation?