Blending Liquids of Different Viscosities

Blending liquids of different viscosities

Liquid – Liquid mixing can be a fairly straightforward process when the liquids are of similar or equal viscosity and the liquids are miscible. In these instances, conventional mixing equipment such as stirrers and in-tank agitators will produce satisfactory results. The liquid-liquid mixing process gets more complex when immiscible liquids are to be blended together, such as oil and water for the formation of emulsions.

But a different set of mixing challenges arise when the liquids being processed are of widely different viscosities. For example when mixing High Active Surfactants such as Sodium Laureth Sulfate for use in products such as bubble baths, shampoos, liquid detergents and other cleansing products. The concentration levels at which the High Active Surfactants (HAS) are often supplied can cause problems for conventional mixing equipment. HAS are often sold at concentration levels of 65 – 70% for greater economy when shipping or storing the ingredient. However, at this concentration, the HAS is a high viscosity fluid, so when employing a conventional mixing system such as an agitator or stirrer to dilute the surfactant into water, rather than blending easily into one another, the disparity in the viscosity between the two liquids causes stratification in the mix.

This makes for an unsatisfactory product as globules of the high viscosity liquid/surfactant can remain undiluted. This can lead to long processing times to try and achieve a uniform blend – and vigorous agitation can lead to aeration and foaming problems. This further increases process times and costs as full yield of the ingredient has not been achieved. With some High Active Surfactants there is an additional risk that at certain concentrations they can form an unworkable gel, therefore the mixing/metering system must be capable of maintaining the correct ration during dilution.

High shear mixers can help to solve these mixing challenges and achieve a uniform blend time after time, optimizing your blending processes. Where an agitator tends to move both liquid ingredients around the vessel without actually blending them together, the positive mixing action of a rotor/stator high shear mixing assembly draws the ingredients straight into the workhead. Centrifugal force drives the material to the periphery of the workhead where the liquids are blended instantly. The liquid is then forced out through the stator and recirculated back to the process vessel as fresh material is drawn into the workhead. A circulatory mixing pattern is obtained where the liquid passes through the workhead many times, thoroughly blending the liquid ingredients. This eliminates stratification, reducing mixing times and improving the quality and consistency of the mix. Typically an In-Line high shear mixer would be used for this application, operating on either a recirculation basis or in a single pass, with the HAS being metered into the water stream just prior to the inlet of the mixer.  This has the added advantage that it can be carried out while the process vessel is being filled, a further saving in process time.

Silverson high shear rotor/stator mixers also have a number of other advantages when used in place of conventional mixing equipment. A comprehensive range of workheads and screens is available for all Silverson high shear mixers, offering great versatility and allowing any machine to be adapted to a particular mixing task. These easily interchangeable workheads mean that one Silverson mixer can be used for blending liquids of varying viscosity or forming a stable emulsion as well as emulsifying, homogenizing, disintegrating, dissolving, dispersing, particle size reduction, powder/liquid mixing and de-agglomerating.

Silverson mixers also offer the advantage of being able to scale-up processes without having to re-formulate. There’s no point using a laboratory mixer capable of speeds of 25,000 rpm or more if the results cannot be replicated in production. That’s why Silverson laboratory mixers are designed and built to the same tolerances as larger production scale units. Comparable rotor tip speed and shear rates across the entire product line means scalable results, every time.

This article is published by

For more than 70 years Silverson has specialised in the manufacture of quality high shear mixers for processing and manufacturing ...