Euxyl™ k 903

What is it? Euxyl™ k 903 is a liquid natural broad spectrum preservative manufactured by Ashland. It is compatible with non-ionic, anionic, and cationic formulations.

Euxyl™ k 903 is comprised of (source: Formulator Sample Shop):

  • Benzyl alcohol: 78–84%
  • Benzoic acid: 11–13%
  • Dehydroacetic acid: 6.5–7.5%
INCI Benzyl Alcohol (and) Benzoic Acid (and) Dehydroacetic Acid (and) Tocopherol
Appearance Clear yellow liquid
Usage rate 0.4–1.2%; tests from Ashland show it is effective at 0.8–1%
Scent Slight chemically scent with a vague almondy whiff. This scent is soft but noticeable in products that are otherwise unscented.
pH 3.0–4.0
Solubility Euxyl™ k 903 is approximately 1.2% soluble in water and readily soluble in polar solvents.

From Ashland: “Euxyl™ k 903 preservative is only limitedly soluble in water. 100g of water at 20°C dissolve 1.2g of Euxyl™ k 903 preservative. In polar solvents such as 1,2-propylene glycol, propanol or acetone, Euxyl™ k 903 preservative is readily soluble. In polyalcohols such as glycerol and sorbitol Euxyl™ k 903 preservative is moderately soluble. In aliphates with hydrophilic groups such as 2-octyldecanol and isopropyl myristate, Euxyl™ k 903 preservative is limitedly soluble. In pure aliphatic solvents it is slightly soluble.”

Why do we use it in formulations? Euxyl™ k 903 is a preservative; we include it in our formulations to ensure they don’t grow gross things like mould and fungus.
Do you need it? You should have at least one broad-spectrum preservative; Euxyl™ k 903 is a good choice if you prefer natural preservatives.
Refined or unrefined? Euxyl™ k 903 only exists as a refined product.
Strengths Easy to use broad-spectrum preservative. I find Euxyl™ k 903 doesn’t lower the pH of formulations as much as Geogard® ECT and Geogard Ultra™ do.
Weaknesses It does add a bit of a chemically smell to unscented formulations, and I find it thins emulsions a bit.
Alternatives & Substitutions You’ll need another broad-spectrum preservative. Liquid Germall™ Plus is an effective, versatile choice, but it isn’t natural. Natural alternatives include Geogard Ultra™; and Geogard® ECT.
How to Work with It Include Euxyl™ k 903 in the cool down phase of your formulations. It is somewhat heat stable (Ashland states a maximum temperature of 80°C for no more than 4 hours), but the manufacturer still recommends including it in the cool down phase.

Euxyl™ k 903 works best in a pH range of 3–6, with 5–5.5 being recommended. This preservative is more effective at lower pH ranges. I find it lowers the pH of formulations ~0.75–1.5 pH points, depending on the formulation. This drop can often be enough to take the product into the effective range for the preservative.

Storage & Shelf Life Stored somewhere cool, dark, and dry, Euxyl™ k 903 should last a year.
Tips, Tricks, and Quirks “In formulations as a result of the presence of iron ions, e.g. from mineral thickeners, yellow discolorations were observed.” –Ashland
Recommended starter amount 30mL (1fl oz)
Where to Buy it  Buy it from an online DIY ingredient supplier. Mine was a gift from Formulator Sample Shop.

Some Formulations that Use Euxyl™ k 903


Posted on

August 27, 2022