Sulfato de éter Lauril de sódio

Sodium Lauryl Ether Sulfate (SLES), designated INCI Sodium Laureth Sulfate, is the sulfated and neutralized ethoxylate of lauryl alcohol (typically 1–3 mol ethylene oxide per mole fatty alcohol). The product is manufactured as an aqueous paste containing 69–71% active matter (SLES 70% paste) or as high-activity needles of >90% active matter, with CAS numbers 68891-38-3 (unspecified EO) and 9004-82-4 (2 EO). The alkyl chain distribution primarily ranges from C12 to C14, with lauryl (C12) exceeding 70%. SLES functions globally as the dominant primary surfactant in rinse-off personal care formulations, household liquid detergents, and industrial emulsification systems due to its high foaming capacity, electrolyte compatibility, and a reduced irritation profile when compared to non-ethoxylated sodium lauryl sulfate (SLS).

What Distinguishes Sodium Lauryl Ether Sulfate from Primary Alkyl Sulfates?

The insertion of 1–3 ethylene oxide (EO) units between the hydrophobic alkyl tail and the sulfate headgroup fundamentally alters phase behavior and dermatological tolerance. Sodium Lauryl Sulfate (SLS) possesses a Krafft point of approximately 9 °C, meaning solubility drops sharply below ambient temperatures, whereas SLES with 2 EO exhibits a Krafft point well below 0 °C, enabling clear liquid formulations even in cold storage. Comparative human repeat insult patch test (HRIPT) data, as evaluated in the Cosmetic Ingredient Review (CIR) panel reports, show that 15% active SLES (2EO) yields a cumulative irritation index approximately 40–50% lower than SLS at the same molar concentration. The mechanism is attributed to a reduced critical micelle concentration (CMC): SLS CMC ≈ 8.2 mmol/L, while SLES (2EO) CMC ≈ 2.1 mmol/L, reducing the monomeric surfactant fraction available to disrupt stratum corneum lipid bilayers. Additionally, the ethoxylation widens compatibility with hard water; SLES tolerates calcium ion concentrations up to 500 ppm without precipitation, whereas SLS forms insoluble calcium lauryl sulfate at ~180 ppm Ca²⁺.

SLES 70% Paste: Control Parameters, Test Methods, and Allowable Tolerances

Commercial SLES is typically supplied as a 70% active aqueous paste. Specification conformance is verified through standardized internal and regulatory test methods. The table below summarizes critical parameters drawn from technical data sheets of major sulfation units (e.g., Stepan STEOL CS-230, BASF Texapon N 70) and the GB/T 13529-2011 standard for sodium laureth sulfate.

Continuous falling-film sulfation reactors, operating with 4–6% SO₃ in dry air at 35–45 °C, sulfonate the lauryl alcohol ethoxylate within seconds. The narrow temperature window avoids excessive ethylene oxide scission that generates 1,4-dioxane. Post-neutralization vacuum stripping at 80–90 °C and 50–70 mbar absolute pressure reduces residual dioxane to <5 ppm for premium cosmetic grades, aligning with the <10 ppm limit recommended by the European Committee of Organic Surfactants and their Intermediates (CESIO) and the U.S. Pharmacopeia (USP <10 ppm for polyethylene glycolated excipients). Failure to maintain sulfation temperatures below 50 °C or stripping vacuums insufficient (>100 mbar) has been documented on production-scale lines to elevate dioxane levels beyond 30 ppm, requiring supplementary activated-carbon polishing, adding 12–18 hours to the batch cycle.

When High-Electrolyte Formulations Demand EO-Distribution Optimization

Household manual dishwashing liquids and car shampoos frequently contain 15–25% SLES (2EO) in combination with linear alkylbenzene sulfonic acid (LABSA) neutralized with sodium hydroxide. Salt-thickening curves in these systems exhibit a pronounced viscoelastic peak governed by the transition from spherical micelles to wormlike micelles. For a 10% active SLES solution, incremental addition of sodium chloride results in a steep viscosity increase, reaching a maximum of 2500–3500 mPa·s (Brookfield LVT, spindle 3, 12 rpm, 25 °C) at 1.2–1.8% NaCl, after which further salt induces micellar branching and eventual phase separation above 3.0%. This non-linear salt response is absent in SLS systems, where viscosity peaks are lower (1500–2000 mPa·s) and tolerance to salt overload is narrower. Plant-scale batch mixing data indicate that premixing SLES with water before adding pH adjusters and salt avoids localized gel domains that form when neat SLES 70% paste contacts undiluted caustic soda, a processing fault requiring 4–6 hours of recirculation to resolve.

The formulation of structured liquid cleansers for suspending polyethylene beads, encapsulated actives, or exfoliating minerals exploits the lamellar phase-forming capability of SLES. At 30–40% active surfactant with an appropriate co-surfactant (cocamidopropyl betaine, CAPB, at 1.5–2.5:1 weight ratio), SLES organizes into stacked lamellar bilayers separated by aqueous domains, creating a yield stress of 0.5–2.0 Pa sufficient to immobilize 1 mm diameter beads indefinitely. Sodium Lauryl Sulfate, with its smaller headgroup, does not spontaneously form stable lamellar structures in binary mixtures with CAPB, instead requiring precise salt and polymer addition, which narrows the process window to ±0.1 °C and ±0.02% electrolyte.

When the Polymer Particle Needs Colloidal Stability: SLES as Anionic Emulsifier in Emulsion Polymerization

In the synthesis of styrene-acrylic and vinyl acetate-ethylene (VAE) latexes, SLES is dosed at 2–4% based on total monomer weight to control particle nucleation and impart mechanical stability. The ethoxylation provides steric stabilization in addition to electrostatic repulsion, enabling latex particles of 100–300 nm diameter to remain dispersible in the presence of divalent cations from fillers such as calcium carbonate. Production experience from 20 m³ semi-batch reactors shows that substituting SLS with SLES reduces coagulum formation during post-polymerization CaCO₃ slurry addition from 0.8% to <0.1% by dry weight. Latices stabilized with SLES also maintain viscosity within 50–200 mPa·s over 6 months of shelf aging at 40 °C, as confirmed by ASTM D7149-05 (Standard Practice for Determining the Freeze/Thaw Stability of Adhesives). However, residual 1,4-dioxane in industrial-grade SLES must be verified below 30 ppm before use in low-VOC architectural coatings to comply with the California South Coast Air Quality Management District (SCAQMD) Rule 1113 volatile organic compound limits.

How OECD 301B Ready Biodegradability Data and Detergents Regulation Intersect for SLES

Under the European Detergents Regulation (EC) No 648/2004, anionic surfactants must demonstrate ultimate aerobic biodegradability exceeding 60% within 28 days per OECD 301B (modified Sturm test) or equivalent. SLES (2EO) consistently achieves 70–85% ThOD within the 10-day window, meeting the ready biodegradable classification. The EC₅₀ for Daphnia magna acute immobilization (48 h, OECD 202) falls in the range of 7–10 mg/L, while fish acute toxicity (Danio rerio, 96 h LC₅₀, OECD 203) is reported at 5–8 mg/L. Downstream blending operations must track 1,4-dioxane not only for skin safety but also because dioxane is classified under REACH as a CMR category 2 substance with a specific concentration limit of 0.01% in the final mixture. SLES grades destined for ECOCERT or COSMOS natural cosmetics require plant-based ethylene oxide sourced from bio-ethanol, with full mass balance audits tracing the C₂H₄O content to non-fossil origins. Without such documentation, certification is denied, creating a critical sourcing bottleneck when only petrochemical EO is available.