Which mixing principles are suitable for homogenising micro-dosages in pre-mixes?
Homogeneous premixes with very low active ingredient contents are a demanding task in solids mixing technology. What matters is not only the type of mixer but also dosing accuracy, particle properties, the tendency to agglomerate, the order of charging, mixing time, sampling and the risk of segregation during discharge.
With dry bulk solids, three mechanisms fundamentally act together:
- Convective mixing: mixing tools or the movement of the vessel transport larger volumes of material through the mixer. This brings about rapid spatial equalisation of concentration and is essential for distributing a premix throughout the overall batch.
- Shear mixing: in shear zones, layers of bulk material slide against one another; interfaces are thereby divided and formed anew again and again. Shear can reduce local differences in concentration and, where necessary, partially break up agglomerates.
- Particulate diffusion: what is meant here is not molecular diffusion but the random relative movement of individual particles within a bulk material in motion. It supports fine distribution, but it is slow and limited with cohesive powders or where particle characteristics differ widely.
For dosages in the range of roughly 1:100 to 1:1,000, a suitable convective mixer with controlled addition and sufficient mixing time may be enough. With substantially smaller proportions, a multi-stage geometric dilution is usually appropriate: the active ingredient is first homogenised with a limited quantity of carrier, and this premix is then diluted further step by step.
If the active ingredient is cohesive or forms stable agglomerates, targeted de-agglomeration can be worthwhile. The energy required should, however, be kept as low as possible and verified by means of representative mixing and segregation trials. A fluidised bed or spray application technique is particularly appropriate where liquid micro-components are to be applied to a carrier, fixed in place or subsequently dried.
Mixing quality must always be assessed with a suitable sampling plan and sufficiently sensitive analytics. A low CV alone does not yet demonstrate robust process capability if sampling, discharge or subsequent transport can cause segregation.
The highest mixing qualities for micro-dosages
Where chemical processes demand precision, mixers, dryers and reactors from amixon® are called for. We develop process technology for powders and solids that mixes reliably, dries gently and allows controlled reactions.
Where micro-dosages have to be processed reliably, mixing quality determines efficacy, product safety and regulatory acceptance. Precision mixers of the HM, VM, AM, KoneSlid® and SpherHelics® series are designed to produce technically ideal random mixtures – with relative standard deviations (RSD) well below 5 %, even at active ingredient proportions in the region of 1 : 100,000. The remaining variance therefore stems predominantly from sampling and analysis, not from the mixing process. For validation purposes this is a decisive advantage.
Ideal premixes as a system performance
These mixing systems make it possible to produce premixes with very precisely defined component contents – from vitamins, enzymes and trace elements through to catalytically active additives. The machines produce a random mixture that cannot be improved upon in practice. This applies to high dosages as well as to very low ones and makes the systems particularly suitable for premixes in pharmaceuticals, food supplements, food and speciality chemicals.
Fill level independence and process flexibility
A further advantage is the extensive independence of mixing quality from the fill level. The mixing systems named can be operated across a wide range of volumes without homogeneity suffering. Operators thus obtain flexible batch sizes at the same mixing quality and reduce the validation effort when products change – an added measure of process reliability in day-to-day operation.
Gentle operation and control of agglomerates
The mixing tools normally work at moderate circumferential speeds and with low heat input. Sensitive carriers, coatings and encapsulated active ingredients remain protected, while cutting tools that can be switched on break up agglomerates in premixes in a targeted manner. At the same time, centrifugal segregation is avoided by design. The result: stable, reproducible distributions that survive transport, storage and filling.
Hygienic design and the pilot plant as the foundation
All the properties named rest on a consistent hygienic design with product-contact surfaces welded free of crevices and ground smooth, top-mounted mixing tools and dead-space-free outlets, together with large inspection doors and integrated washing systems. In the pilot plant, target RSD values, mixing quality and product protection are verified with original products before the investment is made. This produces a sound basis for the decision and a clear picture: amixon® supplies not merely mixers but precise mixing systems with which exactly dosed premixes can be produced reliably and demonstrably.