Polycarbonate (PC)

As requested, we used our Knife Mill PULVERISETTE 11 for the first trial. With the optional single use vessels, even low quantities of sample can be ground (< 20 ml with our 40 ml vessels).

We prepared a batch of 50 grams of sample and placed the sample into our 100 ml vessel. The mill was programmed to maximum speed (14.000 rpm) and we started to grind the particles in short intervals (~ 3 seconds per each). After ~ 30 seconds, a lot of sample was electrostatically attached to the vessel, but no visible grinding success was observed.

We interrupted the grinding process and opened the vessel. A small amount of liquid nitrogen (-196°C) was added into the vessel with the sample. We refilled evaporating liquid nitrogen for about one minute before we placed the closed vessel back into the mill.

Even embrittled, the sample wasn’t comminuted after further 30 seconds of comminution. We aborted the trial at this point. Our Knife Mill PULVERISETTE 11 is not capable to comminute the sample.

For our second trial, we used the sample of result one and fed the sample slowly into our Variable Speed Rotor Mill PULVERISETTE 14 classic line.

The mill was equipped with our Impact rotor with 12 ribs and a sieve ring with 0,5 mm trapezoidal perforations. With maximum speed, typically a d50 < 250 µm would be achieved.

The grinding sound was slightly harsher, but still fine. It took us five minutes until all 50 grams of polycarbonate sample was fed and ground. Rotor and sieve ring were hot, but no sticking, clogging or smearing was observed. A embrittlement of sample (e.g. with liquid nitrogen) does not seems to be required. Surely also higher amounts of sample can be ground this way.

Finest results can be achieved with our Variable Speed Rotor Mill PULVERISETTE 14 premium line. This type of mill can be modified to a high-speed cutting mill. Instead of ~ 3.000 rpm (our Universal Cutting Mill PULVERISETTE 19), this mill is running with up to 15.000 rpm.

Typically with cutting mill conversion, we combine the mill with our high-performance cyclone separator. For this trial, we used the new Small Volume Cyclone (passive, without vacuuming).

A batch of 50 grams was prepared and the sample was slowly fed into the feeding funnel. The cutting sound was fine, only the collecting glass of the passive cyclone was not filled with sample.

The feeding process was finished after 2:40 minutes. Only a few grams of sample were separated inside the cyclones collecting glass. The majority of sample remained inside the grinding chamber; attached to available surfaces by electrostatic charge. We brushed off the ground sample best possible and faced a loss of ~ 3 grams of sample which was removed later on, by vacuuming with a soft brush.

No significant smearing, melting or clogging of sample was observed. On the static knives of the sieve shell holder (typically the hottest point in the mill), we observed a temperature of 54 °C. Cleaning was performed rapidly by vacuuming with a soft brush.