NANOVERMAHLUNG CRYOMILL SAFE AND FLEXIBLE
One particular advantage of the CryoMill is the high operating safety, since the user is at no time in contact with the liquid nitrogen. The nitrogen supply from the integrated autofi ll system is controlled by a temperature sensor so that LN2
is
always replenished in the exact amount that is needed to keep the temperature at -196 °C. The automatic cooling system
guarantees that the grinding process will not start before the sample is thoroughly cooled – this reduces consumption and guarantees reproducible grinding results. With a vibration frequency of 30 Hz, the mill grinds a variety of materials very effectively in a few minutes. The main grinding mechanism is impact, but there is also friction, so that much fi ner grind sizes can be obtained compared with other cryogenic mills. At very high energy inputs, grinding can be interrupted at defi ned moments to dissipate frictional heat from the grinding jar. The mill can also be operated without nitrogen cooling.
GENTLE GRINDING OF PET
Thanks to the wide range of accessories, the applications of the CryoMill are very diverse. For nitrogen supply,
RETSCH offers a 50 liter LN2 tank with safety valve. The grinding jars from 5 to 50 ml can be screwed tightly, so that no sample material can escape. For neutral-to-analy- sis applications, 25 ml grinding
jars made of zirconium oxide or PTFE are available. The offer is completed by different ball sizes and materials, as well as adapters for the use of up to 6 x 2 ml reaction vials.
In order to ensure the best possible adaptation to the different samples, pre-cooling, grinding time, and intervals are freely programmable. During the pre-cooling, the grinding jar is moved at 5 Hz, so that the grinding ball permanently stays in motion and does not freeze in humid samples. By storing up to 9 grind- ing programs (SOPs), routine processes are simplifi ed. LEDs in the display allow to control at any time, which step is current- ly being processed.
PET bottles are popular and widely used as light and robust beverage packaging. Mineral water and other beverages in PET bottles, however, can contain trac- es of the harmful compound acetaldehyde. The sub- stance, even in small traces in the range of 10-20 ppb, has a negative effect on the taste. Therefore, the quality control process of packaging manufac- turers and beverage bottlers involves time-consum- ing and elaborate quantitative test methods. Since acetaldehyde is a highly volatile compound, thermal stress on the PET sample must be avoided in any case before the analysis. Cryogenic grinding at -196 °C is an ideal method for gentle, reproduc- ible grinding of samples made of elastic mate- rials. A heat-induced loss of acetaldehyde during the grinding process is reliably prevented by cooling. The cryogenic grinding is ideal for sample preparation in the context of chromatographic routine checks in certifi ed laboratories.
The preliminary size reduction of the fl exible PET material takes place in a cutting mill such as the RETSCH SM 300 which is ideally suited for this purpose. This mill ensures an adequate preliminary size reduction to a fi neness of about 5 mm without thermal stress on the
material. On this basis, the required fi nal fi neness of less than 0.5 mm can be easily achieved in a second grinding step in the CryoMill. The grinding of a sam- ple of 6 g of pre-crushed preform PET material takes only 5 minutes.
Conclusion
The RETSCH CryoMill has proven to be a perfect instrument for grinding of temperature-sensitive materials with a glass transition temperature below room temperature. The fi nal fi neness is signifi cantly higher than compared to other cryo- genic mills. For materials with volatile components, the CryoMill is the ideal instrument for sample preparation.
PET preforms after preliminary size reduction in the SM 300 (center) – 1200 min-1 section rotor.
, 6 mm sieve, parallel
After fine size reduction in the CryoMill (right) – 50 ml grinding jar of stainless steel, 1 x 25 mm grinding ball of stainless steel, 30 Hz, 2 x 2 min with 1 min intermediate cooling.
www.retsch.com | the sample 39 | page 17
Direct contact: 866-473-8724
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