Ion exchange resins

After 7 minutes of dry grinding, sample has been ground to fine powder; only a few particles seem to be still intact. After 10 minutes of dry grinding, the sample starts sticking to bowl and balls. This uses to happen after the majority of particles reached a fineness of < 20-30 µm. Interacting forces between fine ground particles will become bigger as their own g-force. Therefore, particles will stick to each other and become compressed by the used grinding balls. These clusters of particles also contain bigger particles which will not be ground any further.

We took out a small portion of sample for demonstration.

For a further grinding success, a grinding in suspension is required. For this, we added 110 ml of water after 10 minutes of dry grinding.

To avoid over pressure, we ground the sample in steps of 5 minutes, followed by a programmed pausing time of 10 minutes. After several cycles, the outside temperature of the bowl should be checked (remain below 80°C); grinding time or programmed pausing time might be readjusted afterwards.

After 15 minutes of grinding time, still a few particles with up to 200 µm could be found by optical microscopy. Those particles could still be found after 30 minutes of total grinding time.

Probably a change in ball size (e.g. 10 mm Ø) will be suitable for a further comminution (will be tested with second sample in following trial).

With bowl and balls made of steel, abrasion will grayly discolor the sample rapidly. For a grinding in suspension, we recommend not using water because of possible pressure building. We recommend using alcohol or other organic solvents. After 10 minutes of dry grinding with 20 mm Ø steel balls, we added 120 ml of ethanol and ground stepwise (mentioning the temperature) for a total of 30 minutes. We took small portions of sample after 10 and 20 minutes of grinding for demonstration.

After 30 minutes of grinding we changed the balls to 5 mm Ø for an optimum grinding result.

After 60 minutes of grinding, sample filled the bowl to the maximum and viscosity has been too thick. We took out a small portion of ~ 30 ml of sample and added ~ 70 ml of ethanol to maintain a motor oil like slurry again (for a best grinding result).

We proceeded grinding to a total of 120 minutes. It has shown that the result after 90 minutes of grinding and 120 minutes have been equal. For this, no further grinding success has been achieved after 90 minutes with the present ball diameter. It might be possible to improve the grinding result with a further change of ball diameter (e.g. 1-2 mm Ø).

Grinding results has been determined by our Laser Particle Sizer ANALYSETTE 22 NanoTec plus. Find the measurements after 30; 60 and 90 minutes on separate page.