SLES 70% паста - низкий уровень диоксана

Designated as an aqueous anionic surfactant paste, SLES 70% Paste – Low Dioxane Grade consists of sodium laureth sulfate with an average ethoxylation of 2 moles ethylene oxide per mole fatty alcohol, an alkyl chain distribution centered on C12–C14, and nominal active-matter content of 68–72 %. The material identity is sodium lauryl ether sulfate, CAS RN 68891-38-3, with INCI name sodium laureth sulfate. The low-dioxane designation describes a process-grade class produced by post-sulfation vacuum stripping of the neutralized paste, so that residual 1,4-dioxane is controlled at ≤ 10 mg/kg rather than the 20–100 mg/kg range commonly reported for standard sulfated ethoxylate pastes. The product model code is supplier-specific; the low-dioxane suffix does not alter the sulfated surfactant backbone, the unsulfated matter specification, or the electrolyte response. Its primary position is as a primary anionic surfactant in rinse-off cleansing formulations, liquid laundry and dish detergents, and industrial hand cleaners where high active matter and reduced by-product levels are specified in raw-material quality protocols.

Table 1. Representative release specification for SLES 70% Paste – Low Dioxane Grade.

What Drives Residual 1,4-Dioxane in Sulfated Ethoxylate Pastes?

Residual 1,4-dioxane is not added to SLES; it forms as an intramolecular cyclization by-product during sulfation of the ethoxylated fatty alcohol. The mechanism involves acid-catalyzed back-biting of the ethylene oxide chain under the conditions of sulfur trioxide or chlorosulfonic acid sulfation. The rate of formation increases with free acid concentration, localized reactor temperature, and residence time in the falling-film sulfation unit. After neutralization with sodium hydroxide or sodium carbonate, the already-formed dioxane remains in the paste unless a dedicated stripping operation is installed. Standard SLES 70% pastes are therefore sold with residual dioxane concentrations commonly reported between 20 mg/kg and 100 mg/kg; low-dioxane grades reduce the value to ≤ 10 mg/kg, and some supplier codes specify ≤ 5 mg/kg for high-end cosmetic raw material programs.

The stripping step exploits the vapour pressure difference between 1,4-dioxane, with an atmospheric boiling point of 101 °C, and water under reduced pressure. Supplier technical bulletins describe wiped-film or thin-film evaporators operated at moderate temperature and reduced pressure; exact pressure, residence time, and condenser design are process-specific and not disclosed in most published literature. The important product consequence is that the sulfated active matter is not altered: the molecular weight distribution, the average ethylene oxide number, and the anionic titration response remain aligned with standard SLES 70% paste. Published engineering data for thin-film stripping of SLES paste specific to low-dioxane grades are limited; most technical evidence is confined to supplier specification sheets and headspace GC-MS release data.

For release control, 1,4-dioxane is quantified by static headspace gas chromatography with mass-selective detection. A representative sample preparation equilibrates a diluted paste aliquot at 60 °C in a sealed vial; selected-ion monitoring of m/z 88 and m/z 58 provides quantification limits around 1–5 mg/kg in surfactant matrices. The use of US EPA Method 8260D or an equivalent isotope-dilution procedure is standard because direct injection GC-FID gives poor reproducibility at ≤ 10 mg/kg due to co-eluting surfactant-related volatiles.

Regulatory exposure to 1,4-dioxane is constrained by Article 17 of Regulation (EC) No 1223/2009, which addresses unavoidable traces of prohibited carcinogenic, mutagenic, or reprotoxic substances. 1,4-Dioxane is not an intentional cosmetic ingredient; its presence as a technical impurity is minimized under good manufacturing practice. The California Office of Environmental Health Hazard Assessment lists 1,4-dioxane under Proposition 65; use of a low-dioxane SLES raw material is one element in reducing final exposure, although the finished-product concentration also depends on other ethoxylated raw materials and water quality. If the paste is used at 10 wt% active matter and contains ≤ 10 mg/kg 1,4-dioxane, the theoretical maximum contribution from this raw material is 1 mg/kg in the concentrate before additional dilution or contribution from other ingredients.

Handling requirements for the low-dioxane grade do not differ from standard 70 % SLES paste. The material is shear-thinning; an apparent viscosity value without spindle and speed is not comparable between suppliers. Bulk storage uses 316L stainless steel or high-density polyethylene-lined vessels. Viscosity increases sharply below 15 °C; warming to 30–40 °C under low-shear recirculation restores transfer viscosity. The sulfate ester linkage is hydrolytically unstable at pH below 2.0 and at sustained temperatures above 80 °C; therefore the paste is held at its native pH 7.0–9.0 and not blended with concentrated mineral acids. Contact with strong oxidizers is avoided because cleavage of the ether sulfate releases fatty alcohol ethoxylate and inorganic sulfate.

When Low-Dioxane Paste Enters Cold-Process Surfactant Systems

In cold-process manufacturing, the water phase is maintained at 20–30 °C and the paste is added to water under agitation, not reverse-added. Production-scale vessels fitted with counter-rotating anchor agitators and side scrapers at 30–60 rpm, followed by a short high-shear dispersion step of 5–10 min, prevent localized hydration gel lumps. The paste is typically diluted to 10–15 % active matter for a rinse-off cleansing base. Sodium chloride is added at 0.5–2.0 wt% of batch to build viscosity; the salt curve passes through a maximum and then falls with further electrolyte. The peak position depends on active-matter content and co-surfactant ratio, not on the dioxane stripping step, because the stripping operation does not alter the alkyl chain distribution or the sulfate ester density.

Foam height is measured by the Ross–Miles method under ISO 696. Direct published comparative foam-height data for low-dioxane versus standard SLES 70% paste are limited; equivalence is inferred from the unchanged active-matter content and ethoxylation distribution. Formulations targeting 4,000–8,000 mPa·s at 25 °C measured by Brookfield RVT spindle 5 at 20 rpm can be obtained with the same electrolyte levels as standard SLES. No additional salt is introduced by the vacuum stripping process because the manipulated variable is the volatile fraction, not the inorganic sulfate content.

Typical use levels in rinse-off formats are 5–15 % active SLES as the primary anionic surfactant, adjusted with co-surfactants such as cocamidopropyl betaine at 1–4 % active to modify foam quality and viscosity build. The low-dioxane grade is compatible with nonionic alkyl polyglucosides and amphoteric systems; compatibility with high-charge-density cationic polymers requires charge screening because anionic–cationic complexation can precipitate in the mixing tank. In hard water, the ethoxylate spacer of SLES produces a calcium-ion tolerance profile different from non-ethoxylated sodium lauryl sulfate; calcium chloride precipitation tests are used to quantify that difference, although published data specific to this low-dioxane grade are limited.

Microbial control in the 70 % paste relies on low water activity rather than added preservatives. Closed vessels exclude external contamination. Once diluted below 20 % active matter for use, the aqueous system is susceptible to bacterial, yeast, and mold growth; a preservative system selected for surfactant compatibility is added. The low-dioxane grade does not modify the preservative demand because the stripping step does not add a biocide or alter pH. Batch-to-batch variation in dioxane content is monitored by headspace GC-MS; typical release testing uses a limit of quantitation of 5 mg/kg against a specification of ≤ 10 mg/kg to avoid rejecting material due to analytical noise.

Specification Divergence and Equipment-Release Comparisons

Where the low-dioxane grade diverges from a standard SLES 70% paste is in the residual 1,4-dioxane specification and, in some supplier datasheets, colour. Table 2 compares representative databook ranges; supplier-specific values may differ.

The comparative data show that actives, unsulfated matter, and sulfate remain within the same release windows. This is expected because dioxane stripping removes a volatile by-product; it does not remove sulfated active matter. The low-dioxane grade should not be confused with sodium lauryl sulfate or sodium coco-sulfate. Sodium lauryl sulfate is not ethoxylated and therefore does not generate dioxane by the same route, but it has a different alkyl sulfate structure and different hard-water and irritation profile. Sodium coco-sulfate may contain a different chain distribution. The low-dioxane SLES 70% paste also differs from SLES 28% liquid low-dioxane grades in water content and logistics: the 70 % paste reduces transport water and has lower water activity in closed storage, while 28 % liquid is easier to pump at ambient temperature and may require a preservative system after dilution.

Supplier naming conventions vary. Some codes use “SLES 70% LD,” “SLES 70% low dioxane,” or “SLES 70% cosmetic grade with low 1,4-dioxane.” The common technical discriminator is the residual dioxane release limit and the analytical method. A purchaser should require a batch-specific certificate of analysis showing active matter by ISO 2271 and 1,4-dioxane by headspace GC-MS; periodic dioxane screening alone is not equivalent to lot-wise release testing.

The vacuum stripping unit introduces a process cost and can extend batch time; published data on equipment throughput are limited. The production bottleneck is typically the thin-film stripping capacity rather than the sulfation reactor, because the paste must be held at elevated temperature long enough to remove dioxane without triggering ester hydrolysis. This creates a narrower finishing window than standard paste. If the temperature is pushed above 80 °C to accelerate stripping, the sulfate ester hydrolysis rate increases; if the temperature is too low, stripping time increases and batch throughput falls. Supplier data sheets do not always disclose this window; production-scale observations are seldom published in consolidated form.

Transfer piping for cold paste should be designed for high viscosity at 15–20 °C. Positive-displacement pumps, such as progressive-cavity or lobe pumps, are used rather than centrifugal pumps because the paste has high low-shear viscosity and poor suction behaviour at ambient temperature. Heating jackets on transfer lines are set to 30–40 °C to reduce pressure drop without reaching hydrolysis-prone temperatures.

pH is measured in 2 % aqueous solution under ISO 4316. The paste has a high pH due to residual alkalinity from neutralization; this alkalinity must be acid-adjusted in finished formulations to 5.0–6.5 to match skin pH and optimize preservative performance. Citric acid or lactic acid are used; strong mineral acids are avoided because localized low pH can hydrolyze the sulfate ester before bulk mixing is complete.

Low-dioxane stripping may also remove a portion of other low-molecular-weight volatile by-products, including acetaldehyde and short-chain aldehydes, which can alter the headspace odour profile of the raw material. Published sensory data are limited and not standardized; odour comparison is typically evaluated by a trained panel using a defined dilution protocol. The reduction in dioxane is analytically quantified, but odour differences should not be assumed without panel data because residual odour can originate from the fatty alcohol feedstock rather than from sulfation by-products.

Occupational exposure to 1,4-dioxane in the low-dioxane paste is reduced relative to standard paste, but process ventilation and skin-contact controls are still governed by the surfactant paste properties rather than by the trace dioxane content alone. The paste is an eye and skin irritant at high active matter; pH 7.0–9.0 does not preclude irritation from the surfactant itself. Eye protection and impervious gloves are required when handling undiluted paste; the safety data sheet remains the control document.

The phrase “low dioxane” is not equivalent to “dioxane-free”; analytical detection limits mean that absence cannot be demonstrated. Specifications therefore use a positive release limit of ≤ 10 mg/kg or ≤ 5 mg/kg, not zero.