Ultrafine Grinding of Small Quantities Ultrafine Wet Grinding? Give it a Spin!

From Stefan Mende, Simone Marazzita*

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When developing a nanoformulation, innovative strategies and equipment are essential to success — but typical preparation processes often require minimum quantities. Extensive screening via a method that is both fast and economical can therefore become one of the most important steps in bringing a product through the development phase.

Two turntables on a central rotor ensure reliable and gentle fine grinding of very small quantities in the Deltavita.
Two turntables on a central rotor ensure reliable and gentle fine grinding of very small quantities in the Deltavita.
(Source: Netzsch © Djero Adlibeshe - stock.adobe.com )

Funfair visitors know breakdancers as amusement rides that combine the movement of several gondolas on a turnstile-shaped hub, itself mounted on a rotating turntable. The hubs rotate in the opposite direction to the platform, causing the acceleration to overlap in different directions. The fast-paced ride with its jumbled, swirling seats is a highlight for many visitors and a popular meeting place. A similar principle is now available for grinding, dispersing and mixing of smallest amounts of product — albeit without the light show and hip-hop sounds.

Especially in the field of research and development, for example for formulation development, raw material selection or process development, it is necessary to carry out extensive screening with the smallest amounts of available substance. Ideally, several samples should be able to be processed simultaneously. The new Deltavita 1 grinding system for ultra-fine grinding of very small quantities enables simultaneous grinding of up to 40 different samples with different compositions or different grinding media.

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The new development by German fine grinding specialist Netzsch uses mainly cost-effective standard sample containers which can be disposed of after the test has been carried out. This helps to minimize the cleaning effort, solvent requirement and the time required, the process specialists explain. The quality control of raw materials for production is another important area of application for the Deltavita 1.

Efficiency at Smallest Volumes

The grinding system itself operates according to the principle of a dual centrifuge that is based on the advanced development of a classic centrifuge. In contrast to a conventional centrifuge rotor, the rotor is equipped with two rotary plates which can be fitted with different plastic inserts to hold sample containers. Inserts for 2-milliliter twist-top vials, 10-milliliter injection bottles, 15-milliliter and 50-milliliter Falcon tubes, 125-milliliter beakers or 30-milliliter steel vessels are currently available as standard.

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The power transmission for the rotation does not use a typical V-belt mechanism, which means that it takes a few seconds longer to accelerate up to the maximum target speed of 2,500 revolutions per minute. In return, heat generation and contamination of the unit chamber, which would otherwise be caused by abrasion on the belts, have been minimized.

In addition, the Deltavita’s chamber is equipped with a powerful cooling system that allows for a cooling down to temperatures as low as –20°C, so that samples can be tested for several hours without interruption.

A novel and patented feature is the positioning of the samples slightly tilted at an angle of approximately 40°. Similar to a planetary ball mill, the rotation on the primary path is therefore superimposed by an additional rotation around the axis of the rotary plates. The combination of the sample positioning and the additional rotation causes the direction of the strong centrifugal acceleration in the sample containers to change very rapidly during the process, which in turn causes the sample material to be accelerated continuously and at high frequency in a different direction.

If the sample containers are now partially filled with grinding media, the result is a mill with a freely moving grinding media, which delivers reproducible comminution results with as little as 1 milliliter of suspension and which can thus be used for very efficient grinding processes.

The Formulation Matters

The formulation, that is the proportions of pigment, solvent and binder, but above all the dispersant, also has a decisive influence on the viscosity and stability of a preparation. In the present example, the optimal wetting and dispersant content should be determined in relation to the pigment.

For further optimization, several samples with different concentrations of the dispersant must be processed. Comparing the viscosity of the sample materials produced then makes it possible to identify the optimal ratio of dispersant to pigment, which is represented by the minimum viscosity and the corresponding formulation. For this task, the preparation of five to six samples is typically required. With the Deltavita 1, however, only a small amount of pigment is needed. Furthermore, it is possible to process all samples simultaneously.

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The time needed is about 1.5 hours, including sample preparation, processing and all necessary analyses. Due to the use of disposable sample vessels, no cleaning is required. With the Deltavita 1 grinding system for ultrafine grinding of very small quantities, feasibility studies, product and formulation development or sample preparation for analyses or quality control are possible for a wide variety of product groups.

Ideal for Sensitive Materials

This small and handy machine is characterized by its intuitive operation. Only very small quantities of material are required for the tests to be performed. Different formulations or grinding media sizes can be tested simultaneously, so the results are available very quickly. Time-consuming cleaning, as with an agitator bead mill, is not necessary. Furthermore, the results of the Deltavita 1 can be transferred to agitator bead mills.

Due to the very efficient cooling of the device chamber and despite the high possible energy input, tests with long run times can also be carried out with no pauses, without fear of product overheating. Even temperature-sensitive pigments can be processed without any break time. n

* *The author is Manager of Technical and Scientific Communication (Mende), Sales Area Manager Italy (Marazzita) at Netzsch