PET Flakes

In our first trail, we took the Universal Cutting Mill PULVERISETTE 19 which might be more suitable for this kind of application.

We used a V-cutting rotor and fixed knives made of hardmetal tungsten carbide. This rotor is not as sharp as a V-cutting rotor made of steel (because of a different angle), but shows a much higher durability. For a daily grinding of such small amounts of sample, the standard rotor with V-cutting edges made of tool steel should be suitable.

By using a cutting mill, usage of liquid nitrogen is only necessary for a grinding of thermoplastic samples which will start to melt very fast.

After 30 seconds of grinding, we achieved an output of 26 g of ground sample. After 1 minute, already 30,7 g of ground sample have been found in the collecting vessel. After a total of 90 seconds of grinding, 31,8 g of ground sample have been found.

Typically, a residue about 3 g of sample use to remain inside of the grinding chamber of a cutting mill; like in this case, only a small quantity of ground sample use to lay loose on top of the used sieve cassette, a small amount use to stay in front of the first knife and fine ground sample particles use to stick by electrostatic charge to the housing of the machine. No melted sample has been found inside of the grinding chamber, the cleaning of the machine use to be done rapidly by vacuuming with a soft brush.

Instead of a 1,0 mm sieve cassette, only 0,75 mm sieve cassette has been used in the second trial.

During grinding, output uses to rise slowly. After 30 seconds, 17,5 g of sample have been found in the collecting vessel. After 1 minute, output rose to 25,5 g. After 2 minutes, 29,05 g have been found and after a total grinding time of 3 minutes, already 30,5 g of ground sample have been found.

Like in our first trial, bit of residue inside of the grinding chamber can be removed easily by vacuuming with a soft brush.

Sample 1 has been ground equally, with 0,75 mm trapezoidal perforated sieve cassette, we found an output of 23,8 g after the first minute of grinding. After 2 minutes, 27,2 g of ground sample has been found in the collecting vessel. After a total of 3 minutes of grinding, 28,8 g output has been found. We aborted the grinding process after 4 minutes with a total output of 30,0 g.

No sample started to melt on rotor and knives. A grinding of higher amounts is possible. Electrostatic charged sample residues inside of the grinding chamber can be removed by vacuuming with a soft brush.