High-Shear Mixers for Toothpaste Manufacturing

Toothpaste manufacturing is a demanding process that requires mixing equipment capable to handle viscous pastes, high solid concentrations and abrasive particles. Ultrasonic high-shear mixers provide high-intensity shear forces that provide thorough wetting of powders, uniform homogenisation of colloidal slurries and even particle size distribution. Available at industrial scale and capable to process large volume streams, ultrasonic high-shear mixers are your reliable work horse in toothpaste manufacturing!

ToothPaste Manufacturing

Toothpastes, dentifrices and gels consist in the four main components of water, abrasives, fluorides and detergents. While the water content mostly varies between 20 and 45%, abrasives are the main components contributing with at least 50% to the toothpaste formulation. Widely used abrasives include particles of aluminum hydroxide (Al(OH)₃), calcium carbonate (CaCO₃), sodium carbonate, various calcium hydrogen phosphates, hydrated silicas, zeolites, mica, and hydroxyapatite (Ca₅(PO₄)3OH).
Common toothpaste and dentifrice formulations are manufactured generally following the steps below:
At first, water, humectant (e.g., sorbitol, glycerin, propylene glycol) and other liquid ingredients are blended together so that a liquid base is obtained.
To obtain a certain rheology annd texture of the final toothpaste, rheology modifiers and binders are added to the liquid base. Rheology modifiers and binders give toothpaste its thickness and texture. Commonly used binders include karaya gum, bentonite, sodium alginate, methylcellulose, carrageenan, and magnesium aluminum silicate. Some rheology modifiers require to be pre-blend with non-aqueous liquid ingredient such as glycerine or flavouring essential oils. Alternatively, the rheology modifier can be mixed into other powdered ingredients in order to facilitate the colloidal dispersion.
In the next step, active ingredients (e.g. calcium fluoride, zinc chloride, hydroxyapatite), sweetening flavour additives and preservatives are mixed into the blend.
Then, a slurry containing abrasive particles and / or fillers is incorporated into the toothpaste blend. Since abrasives are the main ingredient, that are added to a high solid load, powerful, reliable high-shear mixing is required to fulfil this demanding task.
Afterwards, flavour and colouring additives are added.
In the final mixing step, a detergent or sudser (foaming agent) that acts as stabiliser and improves the uniform distribution of toothpaste during teeth brushing, is added to the formulation. The detergent and sudser are mixed into the toothpaste blend at a gentle intensity to minimize foaming. Common sudsers are sodium lauryl sulfate, sodium lauryl sulfoacetate, dioctyl sodium sulfosuccinate, sulfolaurate, sodium lauryl sarcosinate, sodium stearyl fumarate, and sodium stearyl lactate.

A typical basic toothpaste formulation consists in:

• Water
• Abrasive particles
• Humectants (e.g. sorbitol, glycerin)
• Stabilizing Surfactants
• Rheology modifiers (thickeners)
• Colouring agents
• Flavouring agents
• Preservatives (e.g. p-hydrozybenzoate)
• Detergent

Depending on the type of toothpaste product, other active ingredients such as bactericides, whiteners, fluoride, etc. are added.

Natural, Clean-Label Toothpastes

Manufacturers of organic, natural toothpastes formulate products using only organically certified and / or natural ingredients. Natural toothpaste brands cater to the demand of health-conscious consumers, who want to avoid the artificial ingredients commonly found in regular toothpastes. Due to consumers’ up-trending demand for clean label products, more and more smaller as well as larger well-known brands offer clean-label toothpastes. Ultrasonic mixers are ideal for small and mid-size manufacturing scale, too. As a non-thermal, purely mechanical mixing method, ultrasonication does not alter natural, organic formulations. Ultrasonic mixing is compatible with natural ingredients such as baking soda, aloe vera, eucalyptus oil, myrrh, plant extract (e.g. sage, mint, strawberry extract), and essential oils (e.g. mint, spearmint, cinnamon).
Read more about ultrasonic shear mixers for the production of clean-label beauty products!

How Does High-Shear Mixing by Sonication Work?

Ultrasonic high shear mixers use the same mechanical principle as other commonly used industrial mixing systems, e.g. high shear blade mixers, multi-shaft mixers, colloid mills, high pressure homogenizers, and blade agitators. Ultrasonic high-shear mixers are frequently used to disperse and mill particles, to emulsify oil and water phases, to wet and solubilize solid matter as well as to produce homogeneous mixtures of any kind of liquids and slurries. Ultrasonic mixers transmit the high-shear forces via an ultrasonic probe into a mixing vessel, such as into a batch tank or into a flow cell. The probe of the ultrasonic mixer vibrates in the liquid at a very high frequency and amplitudes thereby creating intense ultrasonic cavitation bubbles in the medium. The collapse of the cavitation bubbles results in powerful shear forces, that disrupt and break droplets, agglomerates, aggregates, and even primary particles. As ultrasonic cavitation generates high-velocity cavitational streaming with up to 1000km/h, the cavitational liquid jets accelerate particles. When the accelerated particles collide with each other, the act as milling media. As a consequence, the colliding particles shatter and are are reduced to micron- or nano-size. In the ultrasonic cavitation field, pressures alternate quickly and repeatedly between vacuum and up to 1000bar. A rotary mixer with 4 mixer blades would need to operate at a staggering 300,000 RPM to achieve the same frequency of alternating pressure cycles. Conventional rotary mixers and rotor-stator mixers create no significant amount of cavitation because of their limitation in speed.

Before and after sonication: The green curve shows the particle size before sonication, the red curve is the particle size distribution of ultrasonically dispersed silica.

Ultrasonic Toothpaste Mixing

Ultrasonic high-shear mixers can be used as batch and continuous inline processors. For highly viscous materials and high volume processing, the use of a pressurizable flow cell reactor is preferred as this allows you to run under intensified ultrasonication conditions (i.e. pressure intensifies cavitation). Furthermore, by using a sophisticated flow setups such as a passage or discrete process setup, the complete toothpaste mixture is forced to pass through the ultrasonic cavitational zone in the flow cell. This ensures that each particle gets the same treatment so that a highly uniform dispersing and blending is obtained.

Ultrasonic Passage Processing

For each process step, which is when a new ingredient blend is added to the liquid base, the paste mixture passes from one tank through the ultrasonic reactor into a second tank. This passage process ensures a highly reliable and uniform mixing result. Whilst during a conventional high-shear batch mixing process excess mixing must be applied to ensure that all particles get dispersed, the ultrasonic flow cell setup is time- and energy-saving, since the processing time is reduced to the minimum treatment per particle.
In conventional high shear batch mixing, some particles get over-processed, whilst some particles never get into the active mixing zone. Using an ultrasonic flow cell reactor ensures that each particle sees the same high-shear treatment. Due to the passage process, every particle is treated at the same frequency and intensity.

Processing Tip: Ultrasonic Mixing under Pressure

Applying pressure to the ultrasonic reactor or flow cell intensifies the acoustic cavitation. Hielscher Ultrasonics supplies various flow cell and reactor types, which can easily be pressurised up to 5 barg. Customized ultrasonic reactors can handle even higher pressures of up to 300barg.

Ultrasonic De-Aerating Effects

Blade agitators and conventional high-shear mixers introduce high volumes of gas bubbles into the mixture, which is a major disadvantage. The de-aeration of the final toothpaste blend requires an additional processing step, which is time- and energy-consuming. During ultrasonic mixing, the entrapment of air bubbles is generally very low when compared to conventional tank agitators and high-shear mixers. Using an ultrasonic flow cell reactor prevents the unnecessary incorporation of unwanted gas bubbles as the mixture is fed from the holding tank in a steady flow in a closed system. In an ultrasonic flow cell setup, the paste mixture is fed at continuous pressure into the ultrasonic cavitation zone. The ultrasonic flow-through setup prevents the unwanted entrapment of gas during the mixing process. Furthermore, sonication is a well-established technique of de-aeration and degassing and promotes the coalescence of air bubbles so that they can rise to the top and volatilize.
Read more about ultrasonic de-aeration and degassing!

The Advantages of High-Performance Ultrasonic Mixers

Ultrasonic high shear mixers create intense shear forces, which have the required impact on particles such as solids, droplets, crystals, and fibres in order to break them down to a targeted size, which can be in the micron or nano range. Easily handling high viscosities and high solid loads, ultrasonic high-shear inline mixers are ideal to process paste products such as toothpastes, dentifrices and gels. The acoustic shear forces achieve a thorough wetting of the powder ingredients and blend them uniformly into a homogeneous paste.
Depending on the particles hardness and brittleness, the ultrasonic process parameters can be exactly adjusted to achieve the aspired mixing result. When compared to alternative mixing methods such as high-shear blade agitators, high-pressure homogenizers, colloid / bead mills, shaft mixers etc. ultrasonic high-shear mixers offer major advantages such as the problem-free handling of abrasives and high solid loadings, the easy and safe operation, low maintenance and robustness.

Batch and Inline

Hielscher Ultrasonics high-performance mixers can be used for batch and inline processing. Depending on your process volume and hourly throughput, inline processing might be recommended. Whilst batching is more time- and labour-intensive, a continuous inline mixing process is more efficient, faster and requires significantly less labour.

Ultrasonic Mixers for Every Product Capacity

Hielscher Ultrasonics product range covers the full spectrum of ultrasonic processors from compact lab ultrasonicators over bench-top and pilot systems to fully-industrial ultrasonic processors with the capacity to process truckloads per hour. The full product range allows us to offer you the most suitable ultrasonic shear mixer for your process capacity and goals.
The scale-up from a smaller ultrasonic mixer to higher processing capacities is very simple since the ultrasonic mixing process can be completely linear scaled from your established process parameters. Up-scaling can be done by either installing a more powerful ultrasonic mixer unit or clustering several ultrasonicators in parallel.

High Amplitudes for High Mixing Efficiency

Hielscher Ultrasonics’ industrial ultrasonic processors can deliver very high amplitudes. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available. The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.

Easy, Risk-free Testing

Ultrasonic processes can be completely linear scaled. This means every result that you have achieved using a lab or bench-top ultrasonicator, can be scaled to exactly the same output using the exactly same process parameters. This makes ultrasonication ideal for product development and subsequent implementation into commercial manufacturing.

Highest Quality – Designed and Manufactured in Germany

As a family-owned and family-run business, Hielscher prioritizes highest quality standards for its ultrasonic processors. All ultrasonicators are designed, manufactured and thoroughly tested in our headquarter in Teltow near Berlin, Germany. Robustness and reliability of Hielscher’s ultrasonic equipment make it a work horse in your production. 24/7 operation under full load and in demanding environments is a natural characteristic of Hielscher’s high-performance mixers.

You can buy Hielscher ultrasonic high-shear mixers in any different size and exactly configured to your process requirements. From treating fluids in a small lab beaker to the continuous flow-through mixing of slurries and pastes on industrial level, Hielscher Ultrasonics offers a suitable high-shear mixer for you! Please contact us – we are glad to recommend you the ideal ultrasonic mixer setup!

The table below gives you an indication of the approximate processing capacity of our ultrasonicators: