Nano Grinding Mills: Tiny Particles Can Be a Big Deal
Justin Klinger, Sep 24, 2020 6:45:00 AM
Nanonization refers to the creation or manipulation of particles ranging in size from 1 nanometer (nm) to 100 nm. Much of biology happens at nanoscale.
Nanoparticles can be fabricated using bottom-up or top-down methods. Bottom-up nanofabrication refers to building particles using chemistry, while top-down describes grinding or milling.
While bottom-up synthesis and form-in-place processes generate high-quality nanoparticles, they are often extremely expensive and require highly specialized, dedicated equipment.
There is no single nano grinding mill; at the same time, not all milling techniques can achieve nanoparticles. Ball mills, wet and dry media mills, and jet mills can all be used to reduce particles to the nano range.
But what’s the benefit of particles measured in nanometers — and what’s the best way to achieve nanoparticles for your product? Let’s zoom in on nano milling technologies, their advantages and disadvantages, and the ways a toll processor can help you achieve this sometimes challenging particle size.
How Small Particles Pack a Powerful Punch
Nanoparticles are in demand across a wide range of industries, including health and beauty, pharmaceuticals, agriculture, optical glass, batteries, ceramics, pigments, and industrial minerals.
In a nutshell, nanonization increases available surface area of a material, which leads to a number of benefits, including:
- Increased uniformity (including not only size but also particle shape and mass)
- Decreased dispersity (dissimilarity of size, measured in Đ or PDI, or polydispersity index)
- More complete dissolution of compounds that are not very water soluble
- Enhanced reactivity and bioavailability
These improvements can make a formulation more effective, reduce potential side effects, and enable less of a compound to be used in a product — and that can improve product cost and sustainability.
Wet Media Milling: A Proven Technique
Wet grinding offers elegant simplicity in achieving nano-range particle sizes. In this method, inert, nontoxic milling media such as resin, glass, or stabilized zirconium oxide is added to the raw material and carrier liquid for milling.
The mill’s action — for example, the motion of a grinding bowl in a high-speed planetary ball mill — generates high-energy shear forces to fracture already small particles into nanoparticles as they circulate with the grinding media. The smaller the milling media size, the smaller the final particle size. Wet media milling produces very good outcomes in terms of both particle fineness and tight size distributions.
Milling media are selected for their ability to grind materials without themselves being ground down, thus preventing contamination of the final milled particles after the separation step.
Fluidized Bed Jet Milling for Nano-Range Particles
Industries’ demand for very fine, dry powder materials are driving innovations in dry milling methods. Fluidized bed jet mills are a good candidate for nano grinding, because fluidization prevents the dry material from agglomerating, or clumping. Dispersing agents can be added in some cases to prevent agglomeration but, in many cases, additives are unwanted in the end product.
Jet milling with superheated steam enables nano-range particle sizes while also drying the feed material. Steam can be introduced into the grinding chamber at higher pressure than air, achieving higher jet velocities and increasing the energy inside the milling chamber. The integrated internal classifier ensures a tight particle size range.
This technique may not be suitable for heat-sensitive materials, but fluidized bed jet mills using superheated steam can achieve nanoparticles in a range of minerals and pigments.
Determining the Right Method for Your Material
Wet and dry milling methods have their advantages and disadvantages. Nanoparticles tend to agglomerate, making them difficult to disperse after grinding. Wet milling addresses this by encapsulating each nanoparticle in the liquid slurry.
On the other hand, wet milling presents the possibility of introducing contaminants into the final product. Dry methods, such as jet milling, can achieve the desired particle size without using milling media — at the same time, jet milling techniques require more energy. Wet mills can also be adjusted to reduce the likelihood of wear to the milling media or grinding chamber.
If a product needs to be in a dry powder format, after wet milling it requires an energy-intensive drying process. Dry milling techniques, including fluidized jet milling with superheated steam can save this step, possibly also sparing costs.
Of course, not all milling techniques are suited for all materials, so experience and scientific know-how are an absolute must. Ultimately, a trusted toll processor’s team that includes material scientists, R&D experts, and technical experts can help you assess the advantages and drawbacks of different milling techniques, and determine the best process for your goals.
Milling methods and technological enhancements make nanonization possible for more materials and industries than ever before — and the right toll processing team can help you achieve nanoparticles for your products.
Learn about milling techniques and more with our Milling Methods Comparison Guide. Just click the link to download. After you’ve had a chance to read it, contact us with your questions; we’ll be happy to be in touch.