Ctitrus Fibers

A desired planetary mill is often used to comminute lower quantities of brittle samples. With a Planetary Mill PULVERISETTE 5 classic line, up to 4x 225 ml of sample volume could be ground simultaneously to maximize the throughput.

Just for demonstration of the desired type of mill, we used our Planetary Mono Mill PULVERISETTE 6 classic line which could be used with 30 mm Ø grinding balls (for higher impact forces) and reduced the speed to 570 rpm, so simulate the impact forces of our Planetary Mill PULVERISETTE 5 classic line.

We started with our standard setup (8x 30 mm Ø grinding balls) and filled the bowl with 15 grams of bulk citric fiber sample. The sample was ground for one minute, but grinding sound indicated after 30 seconds, that the balls sorted themselves and volume of sample collapsed.

We added two more grinding balls to provide interchanging ball positions to make sure, a homogenous abrasion will occur (so grinding balls would remain spherical during longer grinding times), and programmed a comminution in smaller intervals. After each 30 seconds of grinding, a programmed pausing time of 15 seconds was set.

We ground the sample until a total grinding time of three minutes was applied. Afterwards, still fragments up to 5 mm length were found. A much longer grinding time would be required to achieve desired level of fineness. The fibers are not brittle enough to be ground this way. We don’t recommend using such an equipment. Typically, we would recommend a cutting principle to comminute dried organic fiber samples.

Much finer grinding results can be achieved with our Variable Speed Rotor Mill PULVERISETTE 14 premium line. This mill can be converted into a cutting mill with four static knives and three rotor knives. Instead of standard cutting mills with speed settings up to ~ 3.000 rpm, a PULVERISETTE 14 premium line is capable to grind with up to 15.000 rpm. This way, a lot of samples can be ground to < 0,25 mm or even finer. A high-performance cyclone separator is required with this setup.

With this trial, we used sieve shells of 0,2 mm trapezoidal perforation. We prepared a batch of 70 grams and fed the sample continuously into the feeding funnel. It took about one minute until the last fragment of sample was fed. The grinding sound vanished instantly afterwards.

Only a bit of loose sample powder was left inside the grinding chamber. The sieve shells were not clogged significantly. Surely higher amounts of sample could be ground this way. No significant residues are left inside the grinding chamber. Optionally you can improve the output when the residues of the grinding chamber were brushed into the cyclones connecting tube to merge all ground sample inside the cyclones collecting glass. We cleaned the grinding chamber rapidly by vacuuming with a soft brush.

With the last test of citric fiber sample, we used sieve shells of 0,12 mm perforations instead of 0,2 mm trapezoidal perforations. The 185 g of sample were slowly transferred into the grinding chamber; the grinding sound remained smooth during the feeding process.

No obstacles occurred during the feeding process which was finished after 3:20 minutes. Also there was no significant clogging of sieve shell perforations afterwards. A grinding of higher amounts (e.g. 600 grams as desired) should be possible this way.

Only a bit of sample was not transferred into the cyclones collected one-liter glass and remained loose inside the grinding chamber. For an intensive cleaning afterwards, we disassembled the cutting equipment and washed it with warm water. Afterwards, the equipment was placed into our incubator at 50 °C for a rapid drying.

A bit of the output was placed onto a sheet of paper and a spoon was pressed into the heap to demonstrate the present fineness.