SLES 28% жидкость - низкий уровень диоксана

SLES 28% Liquid – Low Dioxane Grade is an anionic surfactant based on the sodium salt of sulfated ethoxylated lauryl alcohol with a nominal ethylene oxide substitution of 2.0 mol/mol. The trade designation identifies a dilute liquid grade containing 27.0–29.0 wt% active matter in water. The low-dioxane classification is a supplier-controlled impurity specification, not a different CAS registry number; the INCI name remains Sodium Laureth Sulfate and the CAS registry number is 9004-82-4. The release specification for residual 1,4-dioxane is a maximum of 20 mg/kg when measured by purge-and-trap gas chromatography with mass-selective detection. A conventional SLES 28% grade sold without the additional volatile-stripping operation typically carries a release maximum of 50 mg/kg. This distinction is relevant in rinse-off personal cleansing, hand dishwashing, and industrial and institutional cleaners where the residual dioxane mass balance in the finished dilution must be controlled. Because the product is a liquid at 25 °C, it can be transferred by lobe, diaphragm, or progressive cavity pumps without the hot-room storage and melt-out required for 70% active SLES paste.

Does the Low-Dioxane Designation Change Anionic Activity or Only the Impurity Profile?

The anionic surfactant structure is not altered by the low-dioxane process. The same C12–C14 alkyl chain distribution and nominal 2.0 ethylene oxide units remain. The functional release method for anionic active matter is direct two-phase titration under ISO 2271; the pH of a 5% aqueous dilution is measured by ISO 4316. Unsulfated matter and sodium sulfate are controlled because they influence clarity and the salt-thickening response; typical maxima are 2.0 wt% and 1.5 wt%, respectively. The only specification shift between conventional and low-dioxane versions is the lower 1,4-dioxane ceiling. The table below compares the two product variants under identical release methods.

The low-dioxane grade does not require reformulation of the anionic actives; it is not a secondary surfactant blend. However, the stripping operation used to reduce dioxane can slightly increase unsulfated matter if process temperature or hold time is not controlled. Therefore the low-dioxane grade is released against the same unsulfated matter maximum as the conventional grade, not against a relaxed limit. The product is also distinguished from 70% SLES paste by dilution state. A 70% paste requires heated storage above 35 °C for reliable pumping, while the 28% liquid can be handled down to approximately 10 °C before viscosity increases and phase separation risk appears.

Control of 1,4-dioxane begins with ethoxylation. In the sulfation of ethoxylated lauryl alcohol, side reactions can cleave ethylene oxide units and form dioxane precursors. The exact dioxane concentration depends on ethylene oxide distribution, sulfation molar ratio, acidified hold time, and neutralization lag. Low-dioxane production therefore uses a tight SO₃-to-ethoxylate molar ratio, minimized acidic hold at elevated temperature, and post-neutralization vacuum stripping. The sulfate ester is hydrolytically sensitive under low pH and heat; stripping is therefore run at reduced pressure rather than at high temperature alone. In production-scale thin-film evaporators, the stripping step reduces residual dioxane by mass transfer from the surfactant film, and the product is then diluted with demineralized water to the 28% active specification. The final product is filtered, cooled below 35 °C, and transferred to closed stainless-steel or high-density polyethylene storage. Published data for the precise stripping pressure and residence time for this specific grade is limited; supplier certificates of analysis demonstrate compliance through batch-release testing rather than through a fixed equipment parameter.

When Residual 1,4-Dioxane in Finished Product Becomes a Release Criterion

Formulators select low-dioxane SLES 28% when the finished product must remain below an internal dioxane budget. The mass balance is linear at constant addition level. If the raw material contains 20 mg/kg and is added at 10 wt% of the finished formulation, the contribution from the surfactant is 2.0 mg/kg. The same addition using a conventional 50 mg/kg grade would contribute 5.0 mg/kg. For leave-on skin, baby cleansing, or oral-care formulations, this difference can determine whether a batch meets a corporate residual solvent limit. 1,4-Dioxane is classified as a Category 1B carcinogen under Commission Regulation (EC) No 1272/2008. It is not an intentionally added cosmetic ingredient; its presence in sulfated ethoxylates is a process impurity. The EU Cosmetics Regulation EC 1223/2009 prohibits the intentional use of CMR Category 1B substances but does not establish a harmonised numerical limit for unavoidable trace levels in finished cosmetic products. Under the Article 3 safety obligation, the residual solvent must remain below the level that would cause a risk to human health. Quantitative published data for finished-product regulatory enforcement thresholds for this specific configuration is limited. Where pharmaceutical or cleaning-validation limits are relevant, ICH Q3C assigns 1,4-dioxane to Class 2 with a permitted daily exposure of 3.8 mg/day and a concentration limit of 380 ppm. The low-dioxane grade is not a pharmaceutical-grade material; the ICH value is a reference only and does not replace cosmetic safety assessment.

Measurement of low dioxane at the raw material level requires gas chromatography with mass-selective detection because the cyclic ether is water-miscible and not readily determined by simple sulfated ash or anionic titration. Purge-and-trap sample introduction is used to separate the volatile from the surfactant matrix; direct liquid injection can contaminate the inlet with nonvolatile sulfate. The result is reported on the certificate of analysis as ≤ 20 mg/kg, which is a release limit, not a typical batch mean. Batch-to-batch variation is expected to be much lower for stripped material, but no public interlaboratory database is available for this specific grade.

Viscosity Response, Salt Thickening, and Cold-Process Handling

Because the product is supplied at 28% active matter, its as-supplied viscosity at 25 °C is low enough for cold-process mixing. Viscosity measurements are performed by rotational viscometry under ISO 3219. The shear-thinning and salt-thickening response is similar to conventional SLES 28%. Sodium chloride addition to a dilute surfactant system reduces the electrostatic repulsion between micelles and produces a non-linear viscosity increase. In formulations containing cocamidopropyl betaine or alkanolamide, a sodium chloride concentration between 0.5 wt% and 2.0 wt% is used; the maximum viscosity is commonly observed near 1.0 wt% sodium chloride. Above 2.0 wt%, viscosity reversal and turbidity can occur, and the system becomes sensitive to temperature cycling. Because the low-dioxane stripping step does not change the ionic head group density, the same salt curve can be used as for the standard grade.

In production equipment, air entrainment is minimised by adding the liquid below the surface in a side-entry agitated vessel. High-shear dispersion is usually unnecessary and can increase foam carry-over. In manual dishwashing systems, the product is combined with hydrotropes such as sodium xylene sulfonate to prevent gel-phase formation. The product has an anionic charge and can form insoluble complexes with concentrated cationic surfactants; cationics should be prediluted to below 1 wt% and added under controlled pH. The material is stable in closed stainless-steel or high-density polyethylene tanks. Prolonged storage above 35 °C can lead to darkening and pH drift; storage below 10 °C can produce reversible haze and stratification. Frozen material should be thawed to 20 °C and gently recirculated before sampling.

Release testing for the low-dioxane grade is structured as follows.

In a production-scale rinse-off body wash, low-dioxane SLES 28% is typically added to the water phase before preservatives. The addition level of 8–15 wt% as supplied is common, but the final level depends on the surfactant system and the target viscosity. Foam screening is performed by the Ross-Miles method under ASTM D1173; published quantitative foam data for this specific low-dioxane grade in finished formulations is limited, so comparative screening against the existing standard grade is used. The low-dioxane grade should not be expected to compensate for poor preservation or poor pH control; it shares the same microbial and hydrolytic constraints as conventional SLES 28%.

In high-water detergent systems, the product is dosed into the vortex of a low-shear mixer before pH adjustment. The final formula pH is adjusted with citric acid or sodium hydroxide after all surfactant components are blended, because the sulfate ester is sensitive to acidic conditions below pH 4.0 at elevated temperature. The product is not compatible with concentrated hypochlorite bleach; addition to oxidising systems should be avoided without compatibility testing.