Sodium Laureth Sulfate or “SLES” is a surfactant widely used in a range of personal care products such as body washes, shampoos and skin care. An international company based in South East Asia has been able to improve the consistency and quality of its products and reduce its mixing times since purchasing Silverson High Shear mixers for their SLES dilution.
The challenges of diluting SLES
SLES is widely supplied as a “High Active” surfactant with a concentration of 65 – 70%. This offers manufacturers economies in transport and storage costs. During processing, SLES must be diluted to around 25 – 28% concentration for use in personal care products.
But during the dilution process, SLES goes through a “transition phase” where at certain concentrations it forms a gel that cannot be processed as it becomes too viscous for most forms of mixing equipment.
Even when not in the transition phase, some formulations are too viscous for conventional mixers and centrifugal pumps.
When handling high active surfactants manufacturers must also be careful not to introduce any air into the mix, as this greatly increases viscosity.
Further issues such as stratification and long processing times to achieve a uniform product can also arise when diluting SLES with conventional agitators.
Agitators produced an inconsistent product after long periods of mixing
Before contacting Silverson, the company had been having issues handling SLES. As they were using agitators for dilution, their mixing times were lengthy, which meant the concentration was not being lowered quickly enough during the transition phase. They were often finding themselves with a thick, unworkable paste resulting in wastage and even longer mixing times as the process had to be restarted.
When the agitators and the pumps they were using for recirculation were able to dilute the concentration of SLES to a workable percentage, the difference in viscosities between the SLES and the water caused stratification in the mixture. This is where globules of the surfactant remain undiluted or partially diluted in the mix which needed to be filtered out, further increasing the processing times. The end result was a poor quality end product and inconsistency between batches.
Introducing high shear
The solution to the company’s problems was the introduction of high shear to the mixing process.
Dilution of SLES or High Active Surfactants is best carried out using a high shear In-Line mixer. Water is charged into the mixing vessel and recirculated by the self-pumping Silverson In-Line mixer. The High Active Surfactant is pumped into the water stream immediately prior to the In-Line mixer. The mixer’s rotor/stator workhead ensures a uniform mix which is then recirculated back into the vessel. This accelerates the mixing times and ensures that the SLES remains fluid.
Prior to purchasing a range of Silverson In-Line mixers, the company tested the process using a Silverson Laboratory mixer. With the laboratory mixer, the SLES was diluted from the 70% concentration straight down to the 27% needed and so the unworkable transition phase was skipped entirely. As Silverson Mixers are built to the same fine tolerances and a common workhead geometry, the results achieved in the laboratory were able to easily be scaled up to the larger Silverson In-Line mixers without the need to reformulate.
Using the In-Line mixer there was no need for additional feed pumps and mixing times and wastage were reduced.
As such the company purchased a range of In-Line models including a High Viscosity In-Line, Ultra Hygienic In-Line mixers and standard In-Line mixers for their processing line. A Verso laboratory In-Line mixer was purchased for further R&D work.
Silverson mixer as standard in every country
The company was so impressed with the Silverson mixers’ performance when diluting SLES that they are now introducing the process globally across their company, citing the Silverson mixer as standard equipment for this application.
In addition to the SLES application, the company also purchased a Flashmix powder/liquid mixing for dispersing CMC and Carbopol for other products they manufacture to reduce processing times and improve product quality.
By having the Silverson In-Line mixer as standard for diluting SLES, the company now benefits from the following advantages:
- The Silverson In-Line mixer has the capability to rapidly blend the water and surfactant, despite the widely differing viscosities.
- Processing times are substantially reduced.
- The self-pumping action of the In-Line mixer can handle higher viscosity formulations and recirculate the product back to the vessel without additional pumping equipment being required.
- The operation is carried out in a closed system, eliminating aeration.
- With large batches the dilution cycle can be commenced during water charging, further reducing process time.
