Mills and grinders are used to prepare samples (of minerals, plants, food, drugs, pigments, and forensic materials, for example) through particle size reduction (comminution). Afterward, samples are analyzed for their components or to demonstrate specific properties. Milling/grinding methods may be classified as impact, crushing, cutting, and abrasion, operations that Glen Mills’ (Metuchen, NJ) director Stanley Goldberg compares to using a “hammer, pliers, scissors/ knife, and nail file.”
Over the last decade, specified target particle sizes have become smaller and size ranges narrower, two factors enabled by more powerful milling/ grinding machines that are safer and easier to clean and more rapidly achieve desired particle sizes.
For the pharmaceutical industry, which is a growing market for mills/grinders, experts believe that many drugs that fail in clinical trials could be improved by producing them as nanoparticles or within very narrow size ranges. Similarly, existing solid drugs might benefit from tailoring their particle size. Lab-scale mills can rapidly produce small sample batches of a drug during product R&D for subsequent testing. “Every major pharmaceutical company in the U.S. uses a planetary mill for that purpose,” says Kyle James, sales manager at Retsch (Newtown, PA).
“Working in nanoscale provides greater bang for the buck,” says Goldberg. “Whether it’s greater coverage area for pigments, taste enhancement for foods, or improved efficacy for drugs, the control of size is important, and smaller is often better.”
Tim Osborn-Jones of Spex SamplePrep (Metuchen, NJ) says throughput is the leading issue factoring into purchase decisions. “Labs are taking in more and more samples and need to process them in a shorter time frame. They have the option of doing one sample at a time manually or employing a miller or grinder that handles multiple samples.” Two other related factors are reproducibility and yield. Analytical labs must be assured that grinding a particular sample under specified conditions will always lead to the same result and provide the same quantity of the target material. Osborn-Jones says price is a relatively minor factor since “the purchase price is paid back relatively quickly, particularly for grinders with automation features.”
Freezer mills (also called cryogenic mills or cryomills) have been around for about forty years. Cryogenic mills pulverize nonbrittle materials by first freezing and then milling them in specialized sample containers.
Although not appropriate for every sample, freezer mills work wonders with samples that typically do not grind well—plastics, rubber, biological articles, and heat-sensitive materials, for example. “When we used a conventional laboratory blender, our product was coarser and took twice as long to grind. Incorporating the freezer mill into our protocols has increased throughput and efficiency,” says Sharhara Anderson at Rice- Tec (Alvin, TX), which researches rice plants and seed.
SM 300 Heavy-Duty Cutting Mill
• Features a powerful, high-torque 3 kW (4.02 horsepower) motor
• Fold-back housing and removable, push-fit rotor allow for quick and easy cleaning
• Capable of processing power cords, batteries, circuit boards and LCD screens to a fineness of <2 mm
• Available in a heavy, metal-free version for contamination-free results
Micron-Master® Jet Energy Mill
• Designed to grind any type of crystalline or friable material, producing product in the size range of 0.25 to 15 microns
• Able to handle materials as diverse as talc and diamonds
• Available with IQ/OQ protocol documentation for Qualification Test Plans
The Jet Pulverizer Company
PULVERISETTE 6 Planetary Ball Mill Premium Line
• Features automatic imbalance compensation and a grinding bowl lock system
• Able to grind larger sample quantities down into the nano range
• Includes a special emptying device with 2 sieves for grinding bowls
• EASY GTM ensures the set grinding parameters are not exceeded
M 20 Universal Mill
• Batch mill suitable for dry grinding of hard and brittle substances
• Double-walled grinding chamber can be cooled with water through two hose adapters
• Grinding chamber is removable for easy cleaning
• Two grinding chambers can be alternatively operated using one drive