SLES 28% – Liquid Detergent & Dishwash Base

Manual hand dishwashing detergent represents the largest single downstream use for SLES 28% in the household cleaning segment, and the formulation behavior of this base is dominated by a salt-thickening threshold that is substantially narrower than for linear alkylbenzene sulfonates. In a typical high-foam manual dishwash liquid, SLES 28% is incorporated at 18–25% w/w as-supplied, equivalent to 5.0–7.0% active anionic matter in the finished formula; active matter is verified by two-phase titration per ISO 2271 or the supplier certificate of analysis. The feed is pre-diluted with demineralized water at 25–30 °C before addition to the main vessel to avoid localized gel formation that occurs when concentrated ether sulfate contacts hard water or a high-electrolyte brine stream. A 316L stainless steel mixing vessel equipped with a low-shear axial turbine, 30° pitched-blade impeller, and wall baffles is used; impeller tip speed is held below 1.5 m/s during anionic addition because excessive shear entrains air and produces metastable foam that persists through filling and reduces apparent density. Cocamidopropyl betaine is added at 2.0–4.0% as foam stabilizer and secondary surfactant, and lauramine oxide at 0.5–1.5% contributes viscosity response and cold-water grease emulsification. The batch is adjusted to pH 6.5–7.5 with 50% citric acid solution, since the as-supplied SLES 28% has a 1% aqueous pH in the range 7.0–9.0 when measured per ISO 4316. Preservative selection is restricted to non-cationic systems such as methylchloroisothiazolinone/methylisothiazolinone at 0.05–0.10% or sodium benzoate at 0.3–0.5% only when pH is below 5.5; benzalkonium chloride at 0.1% causes immediate anionic-cationic complexation, visible as a white precipitate within 20 min under low shear. Sodium chloride is added as a 20% w/w aqueous solution after pH correction and co-surfactant incorporation. The salt curve is non-linear: at 0.5% NaCl, Brookfield viscosity measured at 20 °C using spindle 3 at 12 rpm per ASTM D2196-20 is approximately 150–250 mPa·s; at 1.0% NaCl the viscosity rises to 400–700 mPa·s; the maximum is typically reached at 1.2–1.5% NaCl with 800–1,200 mPa·s. Addition beyond 1.8% NaCl causes a sharp viscosity collapse to below 300 mPa·s, a cliff-edge that is not reversible by simple dilution and generally requires reformulation with a higher chain-length alkyl ether sulfate or an alkanolamide. The final product must remain clear at 5 °C and 40 °C for 72 h; clouding at low temperature often results from insufficient betaine level, residual free fatty alcohol from the ethoxylation route, or hard-water cations above 150 ppm as CaCO₃. Foam performance is evaluated with ASTM D1173-07 using a 0.1% active solution at 25 °C in 150 ppm hard water; a high-foam manual dish product typically produces an initial foam height of 120–180 mm and retains at least 60% of initial height after 10 min. Grease removal is assessed with ASTM D4009-92 under controlled soiled-plate conditions; formulations with a betaine:SLES active ratio above 0.35:1.00 show faster emulsification of lard and vegetable oil soils, but betaine above 3.5% active may suppress the salt-thickening response and require an additional polymeric thickener such as PEG-120 methyl glucose dioleate at 0.2–0.5%. Filling lines use positive-displacement heads rather than gravity filling because the shear-thinning rheology of salt-thickened SLES causes variable fill weights when line speed exceeds 40 units/min. Degassing is not required if impeller tip speed remains below 1.5 m/s, but air bubbles introduced during powder salt addition remain visible for 24–48 h in clear bottles and are a common batch rejection on high-speed lines. For export detergent formulations, Regulation (EC) No 648/2004 Annex VII A requires ingredient declaration for enzymes, preservatives, and fragrance allergens; REACH Regulation (EC) No 1907/2006 Annex VIII exposure scenarios apply to the neat SLES 28% feed and require eye and skin protection during bulk transfer. Biodegradability of the anionic component is typically confirmed against OECD 301B ready biodegradability criteria, with the 10-day window pass reported on the supplier certificate of analysis.

Representative laboratory panel for a manual dishwash base, measured 24 h after mixing with a Brookfield LVT viscometer; freeze-thaw stability was evaluated at the stated temperatures for 72 h.

What Changes When SLES 28% Replaces Linear Alkylbenzene Sulfonate in Built Liquid Laundry Detergents?

In built liquid laundry formulations, SLES 28% is introduced not as a primary viscosity builder but as a low-smear anionic component that remains phase-stable at pH 8.0–9.5 and tolerates sodium citrate and sodium tetraborate better than in-situ neutralized alkylbenzene sulfonic acid. A typical heavy-duty liquid would contain 5.0–12.0% SLES 28% as-supplied, corresponding to 1.4–3.4% active anionic matter, combined with 5.0–8.0% C12–C15 alcohol ethoxylate 7–9 EO and 2.0–5.0% sodium citrate builder. The substitution of SLES for linear alkylbenzene sulfonate reduces the monoethanolamine demand by up to 60% compared with an LAS acid-based formulation, because SLES 28% is supplied as the sodium salt and does not require in-line neutralization exotherms. Addition sequencing is critical: the alcohol ethoxylate is first dissolved in water at 30–35 °C, propylene glycol at 2.0–4.0% is added as hydrotrope and enzyme stabilizer, and only after full nonionic solubilization is SLES 28% charged under low shear. Charging SLES before the nonionic produces a viscous, stringy gel phase at the feed zone, particularly when tap water hardness exceeds 200 ppm as CaCO₃; in one common failure mode, the gel blocks the recirculation pump inlet and necessitates a 24-h warm-water soak before the batch can be recovered. Enzymes are added after the batch is cooled below 30 °C. Protease and amylase are stable for 90 days at 25 °C only if free water content remains above 45% and pH is held between 8.0 and 9.5; above pH 10.0 or in the presence of more than 2.0% free ethanol, protease autolysis accelerates and stain removal on standardized swatches degrades by 20–40%. Optical brighteners such as disodium diaminostilbene disulfonate are incorporated at 0.10–0.20% and must be pre-dissolved in warm water before addition to the anionic/nonionic micellar phase; direct powder addition creates insoluble agglomerates that redeposit on cotton as bright specks. Low-temperature phase stability is measured at 5 °C for 14 days; a well-formulated built liquid remains clear or slightly opalescent, while a visible electrolyte layer indicates insufficient hydrotrope. Stain removal is assessed according to ASTM D4265-14 using sebum, clay, and grape juice on cotton/polyester panels in a tergotometer with six 1-L stainless steel pots and a 40-rpm oscillation cycle at 30 °C and 150 ppm hard water. Viscosity for built liquid laundry is targeted at 300–600 mPa·s at 20 °C, spindle 2 at 20 rpm per ASTM D2196-20; unlike dishwash formulas, this viscosity is normally achieved with a polymeric rheology modifier such as carbomer or hydrophobically modified alkali-swellable emulsion at 0.1–0.5%, not with sodium chloride, because the electrolyte load from builders would push the salt curve beyond its maximum. The high water content of the 28% feed also makes it unsuitable for polyvinyl alcohol unit-dose detergent film, because final water activity above 0.6 causes film softening at 30 °C. For European markets the formulation must meet Regulation (EC) No 648/2004 Annex VI limits for phosphates and Annex VII ingredient disclosure for enzymes and preservatives, while the bulk SLES 28% feed should be accompanied by a REACH extended safety data sheet with derived no-effect levels for freshwater discharge.

Alkaline Degreasing of Polymerized Food Soil at pH 9.0–10.5

Food-processing hard-surface cleaners formulated with SLES 28% operate in a pH band where the ether sulfate linkage remains hydrolytically stable while the formula contains sufficient alkalinity to saponify polymerized fats. A concentrated exhaust-hood and fryer-deck cleaner contains 8.0–15.0% SLES 28% as-supplied, 1.0–3.0% sodium metasilicate pentahydrate, 1.0–2.0% tetrasodium EDTA, 2.0–4.0% sodium citrate, and 1.0–3.0% dipropylene glycol methyl ether. The builder is dissolved first at 35–40 °C; SLES 28% is added only after the metasilicate is fully dissolved, because simultaneous charging of concentrated metasilicate and ether sulfate generates a localized gel that can take several hours to re-homogenize. The pH is adjusted with sodium hydroxide or citric acid to 9.0–10.5; above pH 12.0 the sulfate ester bond undergoes measurable hydrolysis at 40 °C within 72 h, reducing anionic active matter by more than 10% and dropping foam height. Dilution at the point of use ranges from 1:10 to 1:30 with potable water, yielding 0.3–1.5% as-supplied product or 0.08–0.42% active SLES. Soil removal on stainless steel 304 panels is evaluated gravimetrically in a 40 °C immersion cell with continuous recirculation at 0.5 m/s using a lard/mineral oil/microparticulate soil; there is no single ASTM method for this specific food-processing substrate, so plant trials often include a 5-min contact time followed by a 20-psi potable-water rinse. The recirculation pump should be a centrifugal unit with a SS316 impeller rather than a positive-displacement pump, because the high-viscosity gel formed during sequential addition can dead-head a progressive-cavity pump. Foam profile must remain moderate for manual spray-and-squeegee use, with ASTM D1173-07 initial height below 50 mm for a 0.1% active solution at 25 °C; this is achieved by selecting an alcohol ethoxylate with 5–6 EO as the nonionic co-surfactant at 1.0–2.0% rather than a high-foam betaine. For food-contact surfaces, the cleaner is not a sanitizer and must be followed by a potable-water rinse; sanitizing steps are regulated separately under applicable biocide or FIFRA provisions. The use concentration must be verified for pH below 11.5 to avoid caustic labeling under transport and supply regulations.

Unlike manual dish products, vehicle shampoos built on SLES 28% do not share the salt-thickening target of dish liquids, because trigger-foam and touchless pre-soak products are diluted at the nozzle from 1:50 to 1:100 and must remain pumpable as low-viscosity concentrates. A pH-neutral car shampoo concentrate typically uses 10.0–20.0% SLES 28% as-supplied, 1.0–3.0% cocamidopropyl betaine, 0.5–1.5% lauramine oxide, and 0.2–0.5% sodium citrate. The dilution at 1:100 gives 0.1–0.2% as-supplied product, which is sufficient for wetting road film and providing lubricity on clear-coat surfaces. Sodium chloride is omitted entirely; the concentrate viscosity is kept below 50 mPa·s at 20 °C to allow reliable draw through a foam lance venturi with an orifice diameter of 1.0–1.2 mm. Foam stability is measured with ASTM D1173-07 at 0.1% active and 25 °C, with an initial height of 80–120 mm and complete drainage within 10 min preferred for rinsing without residue. The pH is maintained at 6.5–7.5 with citric acid; more alkaline conditions above pH 9.0 accelerate gloss loss on clear-coat panels after repeated washes, while pH below 5.0 begins to remove wax from polymer sealants. Water hardness tolerance of the diluted vehicle shampoo remains acceptable up to 300 ppm as CaCO₃ when sodium citrate is present; without citrate, a hazy precipitate forms within 24 h in hard-water regions. No globally harmonized test method exists for car shampoo lubricity; production-scale validation typically uses a linear friction sled on painted clear-coat panels at 25 °C and 60% relative humidity to compare the diluted formula against water, with the target coefficient of friction at least 30% lower than water without added surfactant. Preservative levels follow the same anionic compatibility rules as manual dishwash: isothiazolinones at 0.05–0.10% are effective, while quaternary ammonium compounds are excluded because they precipitate sodium laureth sulfate and reduce foam height within 48 h.

When a High-Active Ether Sulfate Is Diluted to 7% for Trigger Spray, Phase Stability Dictates Solvent Choice

Trigger-spray laundry pre-spotters differ from the built liquids described above because they require Newtonian or near-Newtonian discharge through a fine orifice and must remain clear in the presence of water-miscible solvents. A typical pre-spotter uses 5.0–10.0% SLES 28% as-supplied, equivalent to 1.4–2.8% active anionic matter, combined with 2.0–5.0% dipropylene glycol n-butyl ether, 1.0–2.0% sodium citrate, and optionally 0.5–2.0% ethanol or isopropanol. The solvent is pre-blended with water and sodium citrate before SLES 28% is added, because direct injection of polar solvent into a concentrated surfactant phase can thin the micellar structure and produce a temporary two-phase haze that persists for several hours. Viscosity is targeted at 10–50 mPa·s at 20 °C, spindle 1 at 60 rpm per ASTM D2196-20, measured after 24 h to confirm equilibrium. No thickening salt is used; the built-in electrolyte from sodium citrate is sufficient to give Newtonian flow, and additional NaCl would create the same viscosity spike seen in dishwash but without the mechanical strength required in a trigger-spray system. The trigger dispenser delivers 1.0–1.2 mL per stroke through a 0.6-mm orifice; above 100 mPa·s the spray becomes intermittent and droplet size increases beyond 200 µm, reducing penetration into cotton interstices. Phase stability is evaluated at 5 °C and 40 °C for 72 h, with cloud point adjusted by the ratio of dipropylene glycol n-butyl ether to ethanol; an excess of ethanol above 2.0% lowers flash point below 60 °C, triggering flammable-liquid storage classification under GHS. Preservative selection for this water-rich trigger-spray system is typically methylchloroisothiazolinone/methylisothiazolinone at 0.05%; DMDM hydantoin may be used only if the released formaldehyde is declared under Regulation (EC) No 648/2004 Annex VII. Stain removal on cotton/polyester is assessed according to ASTM D4265-14 using dirty motor oil, tomato, and grass soil; the pre-spotter is applied at 4 mL per 100 cm², left for 5 min, then laundered at 30 °C. For products containing enzymes, the EU detergent regulation requires enzyme labeling regardless of concentration, and fragrance allergens above 0.01% must be declared.

For general-purpose trigger-bottle cleaning, a ready-to-use all-purpose cleaner is produced by diluting SLES 28% to 1.0–2.0% as-supplied with potable water and adding 0.5–1.0% C9–C11 alcohol ethoxylate; no additional thickener, salt, or co-surfactant is required, and pH is adjusted to 8.0–9.5 with sodium carbonate or citric acid before filling into trigger bottles.