PMMA - (C5O2H8)n

As desired we used to Jaw Crusher PULVERISETTE 1 for a comminution. In our lab we only have Model I of the premium line instrument. Due to the feed size (> 60 mm), we recommend the use of a Model II (for samples up to 95 mm). A classic line Model II could also be used for this purpose.

Our jaw crusher was pre-equipped with crushing plates made of zirconium oxide to grind the sample metal-free. Certainly, crushing plates made of steel can also be used for such a sample.

The gap was set by us to 0.3 mm (smallest gap setting). With this setting, the grinding gap has a distance of 0.3 mm in closed position, but opens > 2 mm wide in operation (with standard kinematics). Generally, fragments up to about 8 mm long are still found in samples ground in this way.

A batch of 100 g was prepared and the individual models were placed in the feed hopper one after the other. The grinding noise after the first PMMA model fed in quickly faded away. For the second model, a soft tapping was heard on the moving crushing plate. This indicates that the model was too large and jammed in the grinding chamber in front of the crushing plate. Possibly, the weight of sample added further could mobilize the PMMA model again. We added the rest of sample. After a short improvement of the noise, a soft knocking noise reappeared.

We mobilized the sample in the grinding chamber by modifying the gap setting. The gap was opened almost completely and closed again several times. In this way, the entire sample was pre-crushed within approx. 60 seconds.

Finally, the discharge was applied one more time at 0.3 mm gap setting. The grinding noise was typical. The sample was brittle and small enough to be ground without problems.

Some fragments > 5 mm were found in the discharge. Residues were not visible in the grinding chamber. Cleaning was quick, using a brush and vacuum cleaner.

Classically, plastics are often comminuted with cutting mills. For a feed size up to approx. 70 mm, we would have advised the larger universal cutting mill PULVERISETTE 19 Large. Here, a metal-free size reduction is not possible.

With this mill, samples up to 120 mm wide can be fed via the protected funnel with sample pusher. If less fine dust is to be produced, it would have been advisable to set a lower speed. We had set our Universal Cutting Mill PULVERISETTE 19 Large to 1000 rpm (300-3000 rpm possible).

A batch of 160 g was prepared and two of each sample were added simultaneously via the protected funnel. Due to the used sieve cassette with a 4 mm square perforation, the sample was ground very quickly and the grinding noise stopped after only a few seconds. The entire sample had been fed after only 40 seconds and no grinding noise was heard after about 45 seconds. The machine was stopped after 50 seconds.

The mill discharge was even slightly finer compared to result 1. Some fine dust was found in the grinding chamber, as well as in the protected funnel. Cleaning was done by brush and vacuum cleaner. Finally, the last residues were removed with compressed air. Certainly, much larger sample quantities can also be comminuted in this way.