Study on Performance Indicators of Sodium Laureth Ether Sulfate (SLES) in Shampoos and Dishwashing Liquids
Sodium Laureth Ether Sulfate (SLES) is the most prevalent anionic surfactant in both personal care and household cleaning products. Functioning as an excellent detergent and foam enhancer material, SLES is largely found in shampoos and dishwasher liquid. Raw material formulators and chemical traders will need to determine the right performance indicators before settling on the best SLES for their product as SLES parameters can affect foaming experience, cleaning capability, product longevity and skin safety of a formulation. This paper will discuss important SLES KPI parameters which would be used in shampoo and dishwashing formula evaluation that can be used in both sourcing and R&D departments.
Dominant Matter
Dominant matter is the first KPI of SLES you should know as the main reason you buy or sell SLES commercial is its active surfactant concentration that will clean and foam the detergent. Commercial grade SLES is offered as waterbased with a common ratio of 28% and 70%. Active matter means only the percentage of active surfactant responsible for cleaning and foaming; the remaining water and minor manufacturing residuals are not counted. For example: 28% SLES is mostly preferred since it minimally impacts batching and also has a low risk of forming gels during mixing. On the manufacturer side, concentrated 70% SLES is cost effective in reducing delivery and warehouse expenses. Lower surfactant content would decrease both the capability of foaming and detergency. Furthermore, variation of the active content may lead to formula instability and hence increasing cost of raw ingredients. Good manufacturers include analysis reports that show the content of dominant matter for each shipment.
Foaming Power & Foam Stability
The capability of a product to foam is one of the indicators of user satisfaction with shampoo and dishwashing liquid. SLES provides excellent fast-forming stable high-density foam. In shampoo, foam helps to remove scalp sebum and hair styling residues. In dishwashing liquid, stable foam maintains cleaning performance while scrubbing greasy tableware. There are various foaming power tests available such as RossMiles test, which determines how high the foam rises under conditions of standard controlled temperature and concentration. Poor SLES foam would be a very coarse foaming texture collapsing very fast. Typically, formulators would mix SLES with CAPB or another co-surfactants to make better use of foam elasticity which has a greater effect in high-grease dishwashing formulas where oil destroys foam very fast.
Viscosity Behavior
On its own, SLES isn't capable of giving a very viscous product. Its property of making a paste-like product depends almost 100% on the addition of sodium chloride. As we see, different SLES batches may yield different salt-soluble viscosity profiles when plotted as functions of salinity.
Shampoo manufacturers typically use salt for viscosity fine-tuning to their product sensory & packaging specifications.
First-rate SLES has a very smooth and consistent viscosity curve: with salt addition the viscosity increases steadily without any sudden thickening phase separation. Dishwashing liquid needs to have lower viscosity for free pouring, therefore the salt tolerance has to be under very strict control.
Inefficient viscosity development will lead to poor batch-to-batch consistency and product rejection.
Unsulfated and Free Oil Residue
The unsulfated matter is a by-product formed when the alkylation reaction doesn't go all the way and the product stays as a partially sulfated compound. Too much unsulfated material is bad as it weakens the foam structure and cleaning action of the detergent. More so, this kind of substance may produce a sticky layer or an oily film in shampoo.
For dishwashing liquid, too much unsulfated stuff may mean inadequate removal of greasy residue.
The presence of free oil is a problem as well. If left undisturbed in the bottle for extended periods, free oil can cause haze, stratification, separation, and even the generation of off-odors.
Established SLES producers make sure that unsulfated matter is within acceptable limits so that their products are visually appealing and can be stored without problems for a long time.
The pH Value
SLES solutions have a pH value normally between 7.0 and 9.0. A weakly acidic pH of 5.5–6.5 is commonly adopted for hair care products such as shampoos because it is closer to the pH level of the healthy scalp and is less irritating to human skin.
Liquids for dishwashing are kept at slightly alkaline pH (or even neutral) so as to preserve their effectiveness and prolong their shelf life.
In the case when incoming SLES has an pH significantly high, more acid will be required during compounding, this resulting in cost increase and possible separation into phases. If pH is too low, the hydrolysis of ether sulfate molecules during storage will be speeded up, therefore degrading the product performance.
Impurity: 1,4-Dioxane & Skin Irritation
SLES is reported to possess lesser skin and eye irritation than SDS (sodium dodecyl sulfate) as a consequence of ethoxy groups in its chain. Nevertheless, a major factor deciding the safety profile of a product is the level of impurities present in the starting material.
1,4-dioxane originates in the ethoxylation process of the ingredients and due to its potentially harmful effects is heavily controlled in the EU, the U.S., and South-East Asia as far as cosmetic raw materials are concerned. The use of low-dioxane SLES for shampoo products, which go close to the eyes and scalp, is required in these regions.
Awareness about mild hand-washing products has grown considerably so dishwashing liquid also requires formulation mild enough to withstand repeated hand washing.
Low residual sulfate has also been identified as one of the most effective ways of preventing skin dryness and tightening after a wash.
Detergency&Grease Removal
At the heart of SLES grease removal is the interplay of hydrophobic and hydrophilic properties. The fatty alcohol carbon chain, through the principle of 'oil attracts oil', adsorbs the oil particles into a micelle-like structure, while the hydrophilic sulfate groups disperse the micelle into water. C12 - C14 chain is the standard grade of SLES, as it offers a good balance between foam level and degree of degreasing. However, if the hydrocarbon chain length is increased, the oil solution capacity would be improved but it will result in the increase of cloud point and lower low-temperature stability.
Unlike the heavy-duty grease removal in dishwashing liquids, shampoo only needs the mild removal of scalping sebum. Therefore, shampoo's co-surfactant formulation is much different from dishwashing liquid.
Cloud Point & Low-Temperature Stability
Cloud point is the lowest temperature of the solution at which the solution becomes opaque or milky. A high cloud point may cause the ready-made shampoo or dishwashing liquid to become cloudy or to separate during storage at cold temperatures and transport across international borders, particularly for consignments to very cold areas.
Freeze-thaw testing methods are used to check the stability of raw materials when subjected to temperature changes. Only stable SLES materials remain clear and will not precipitate, which for the export business supply chains is very essential.
Different KPI Priorities for Two End Products
Shampoo formulation mainly considers active content, dioxane levels at minimal, creamy foam, viscosity controllable and mild.
Dish-washing liquid formulation is targeted at grease detergency, anti-oil foam persistence, low temperature stability and cost efficiency. Employing the same SLES grade for the manufacture of both products can be frustrating either by producing substandard finished goods or unnecessary high material costs.
Regulatory Compliance for Global Trading
In addition to laboratory KPIs, global regulatory requirements cannot be ignored. SLES for cosmetics and household cleaning products have to satisfy REACH (EU), ASEAN cosmetic notifications and local food-contact rules for dish detergent. Those purchasing SLES for cosmetic or cleaning products, or for dish detergents which are meant for food-contact use should obtain all available information from their suppliers, such COA, MSDS, impurity limits and any kind of registration documents prior to purchasing in bulk. International shipments also require UN classification for hazardous or non-hazardous materials, which needs to be confirmed in advance in order to have the materials safely transported and cleared for customs purposes.
Conclusion
Though SLES is still an inseparable surfactant in daily-life chemical products, its real performance greatly depends on a whole range of linked indicators instead of the active content. These include active matter, foaming features, viscosity profile, unsulfated residuals, pH, dioxane impurity, detergency and cold stability. With the help of the right indicator, raw material suppliers and production engineers pick an appropriate SLES grade according to the positioning, regional regulatory standards and delivery conditions.
Pick the correct SLES grade, with the support of these indicator(s) and by the aid of the right partner(s), you can easily prevent formulation failure, decrease customer complaints and at the same time improve your company's total manufacturing cost to the maximum possible of chemical makers of the kind for the day's dailychemicals.
