In their 70 year history Silverson Machines have supplied mixing equipment for a variety of applications in the cosmetics and personal hygiene industries and are continuing to do so during the current pandemic; specifying and supplying machinery for the production of hand sanitisers, liquid and hand soaps and other cleaning products such as wet wipes and household disinfectant products.
Silverson Machines has already supplied several machines to customers for the manufacture of hand sanitiser products including Laboratory scale, Pilot scale and full production scale Batch mixers. A special unit normally used for production of sauces was sent over to Malaysia for this application, assisting in the attempt to reduce transmission of the virus and showing the flexibility of Silverson’s mixing equipment.
There are a number of active ingredients used in hand sanitisers, but the most effective sanitising products are based on alcohol, usually isopropyl or ethyl alcohol. Typically the alcohol content is between 60 and 95%.
This is usually blended with an aqueous dispersion of carbomers such as Carbopol, to provide the gelling effect. But, as with many powder/liquid applications Carbopol has its own set of processing problems that can sometimes be exacerbated by conventional agitators.
Carbopol is a low density powder which tends to float when added to water, requiring vigorous agitation to be incorporated. This can lead to excessive turbulence at the liquid surface, causing dusting problems and aeration. Entrained air is very difficult to remove from the product once the gel has been formed and can cause clear gels to appear cloudy. The entrained air also causes problems when the product reaches the packaging stage as containers are filled by volume rather than by weight.
Further problems can occur as the powder tends to form agglomerates when added to water, and a conventional agitator is unable to break these lumps down and fully hydrate the powder. This leads to poor yield, long mixing times, poor consistency and variation from batch to batch.
To overcome these problems many manufacturers are specifying high shear mixers for this application. Since the COVID-19 pandemic began Silverson Machines has received several enquires as to whether their mixing equipment can be used for the manufacture of hand sanitiser products, and the simple answer is: yes they can!
The high speed rotation of the Silverson rotor/stator workhead forces the carbomer/powder directly into the high shear zone of the workhead, rather than allowing the it to float on the surface of the liquid.
Inside the workhead, any lumps or ‘fish eyes’ that may have formed when the powder was introduced into the liquid are sheared in the precision engineered gap between the rotor and the stator which ensures that when the product is forced out through the stator, all agglomerates are eliminated.
All the while fresh material is being drawn into the workhead, setting up a circulatory pattern of mixing which ensures all the product passes through the workhead many times, but without excessive turbulence at the liquid surface, and therefore aeration is minimised.
Once the carbomer is fully dispersed, the alcohol phase is added. Silverson In-Line mixers allow this to be done via a manifold at the inlet of the mixer, ensuring that two phases are mixed immediately on contact.
The positive mixing of a Silverson mixer ensures functional ingredients such as Carbopol, which may only make up a very small proportion of the overall formulation are correctly dispersed throughout the mix, guaranteeing a homogeneous product, batch after batch.
Silverson manufacture the largest capacity range of any one supplier from batches of 1ml up to 30,000 litres and offer a range of mixers for this application to suit individual process requirements.
For smaller batches, R&D work or pilot production and Batch mixers are most suitable. The Silverson Ultramix is also ideal for higher viscosity mixes such as hand sanitiser solutions.
For larger batches the Silverson In-Line mixers offer completely aeration-free processing as the mixer, pipework and vessel form a closed system.
The Silverson Flashmix can also be used for larger batches; mixing can be carried out in a closed system and powder can be added at a controlled rate minimising dusting problems.
Silverson also offer the advantage of being able to provide mixers suitable for operation in Flameproof areas.
Silverson has produced a video on ‘How to Manufacture Hand Sanitisers’ available on the Silverson website and YouTube channel along with an application report which will help you choose the right mixer for your application.
Contact details:
Website: www.silverson.co.uk
Email: sales@silverson.co.uk
Telephone: +44 (0)1494 786331
Address: Silverson Machines, Waterside, Chesham, Buckinghamshire, HP5 1PQ
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