Nano Grinding Mills: Tiny Particles Can Be a Big Deal
Justin Klinger, Jun 16, 2022 9:22:00 AM
Nanonization (sometimes also called nanoization) refers to the processes used to make particles that range in size from 1 nanometer (nm) to 100 nm. Many biological processes are nanoscale. In the human body, hemoglobin measures about 5.5 nm in diameter. DNA is even smaller — one strand measures just 2 nm in diameter.
Materials can behave very differently at this scale due to the vastly changed volume-to-surface area ratio of particles. And that’s why nanomilling technologies are playing an increasing role in manufacturing advancements in pharmaceuticals, industrial chemicals, coatings, pigments, and more.
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 techniques used to break particles down in size.
While bottom-up synthesis and form-in-place processes generate high-quality nanoparticles, they’re expensive and they require highly specialized, dedicated equipment.
Grinding, on the other hand, uses the same types of equipment as micronization — but with technical experts manipulating and adjusting their operations to achieve the target particle size range.
There is no one type of nano grinding mill, and not all milling methods or equipment can achieve nanoparticles. Ball mills, dry and wet media mills, and jet mills can all be used to reduce particles down into the nano range.
What are some of the advantages 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 how a toll processor can help you achieve this challenging particle size range.
Tiny Yet Mighty Nanoparticles Are in High Demand
A few of the industries where nanoparticles are widely used include health and beauty, pharmaceuticals, agriculture, optical glass, batteries, ceramics, pigments, and industrial minerals.
Why? The answer lies in the power of increased particle surface area.
Nanonization processes vastly increase the available surface area per particle of material. That changes how the material behaves, as well as how easily it can interact with other materials, with living systems, etc. Benefits of achieving these ultrafine particle sizes include:
- Increased uniformity (not only in size, but also in particle shape and mass)
- Decreased dispersity or dissimilarity of size (measured in Đ or PDI, polydispersity index)
- Improved dissolution of compounds that are not highly soluble in water
- Enhanced reactivity and bioavailability
The resulting changes in material properties can make a formulation more effective. It can enable a manufacturer to use far less of a high-value ingredient, or an ingredient that can otherwise cause significant side effects or environmental effects.
These enhancements add up to improved sustainability and cost controls, more effective and better tolerated medications, brighter paints and inks, and even stronger industrial materials.
Wet Milling: A Proven Nano Grinding Method
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. In the wet mill, the material is added to a liquid, often with surfactants or dispersants added, and recirculated through the grinding chamber until the target particle size range is achieved.
The wet mill’s action fractures already small particles into nanoparticles as they circulate through the media. In general, 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 suitability to grind materials without the media being ground down. This is key to preventing contamination of the final milled particles after milling and separation from the media.
Nanomilling in a Fluidized Bed Jet Mill
One downside to wet milling is … well, that it’s wet. For materials needed in a dry state, a drying step is required after wet milling. Drying, in turn, is followed by a deagglomeration step, since ultrafine particles often tend to clump together when dry. In addition, the dispersing agents often used in wet milling can be unwanted in the end product.
Fortunately, industry demand for very fine, dry powder materials is 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.
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 fluidized bed jet mill’s 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.
How to Select the Right Milling 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 dispersant and surfactant additives into the final product. Dry methods like jet milling can achieve the desired particle size without using milling media.
Jet milling processes generally require more energy than wet milling. But if an end product needs to be in a dry powder format, choosing wet milling also means choosing an energy-intensive drying process to follow the milling step. Dry milling techniques, including fluidized jet milling with superheated steam, can save this step.
The bottom line is this: Talk to an expert about which method is most suitable for your material and most cost-effective for your project.
Clearly, not all milling techniques are suited for all materials, either. That’s another reason experience and scientific know-how are an absolute must. Ultimately, a trusted toll processor’s team of material scientists, R&D experts, and technical experts can help you assess the advantages and drawbacks of different nano milling techniques and determine the best process for your goals.
Advancements in milling methods and technological enhancements are making nanonization possible for more materials and industries than ever before — and the right toll processing team can help you achieve nanoparticles for your products. Get started planning your next milling project with our free Grinding Project Checklist. Just click below to download your copy now.