I have a partially crosslinked polyurethane polymer which need to be crushed into fine powder of particle size ~ 100 micron or less. The polymer is tough but gooey or rubbery. We tried the cryomilling. Is there any other way to crush it into fine powder (~100 micron) besides cryomilling.
Thanks
I shared a postgraduate research laboratory, long time ago in the U.K., with a schoolmate who used to work on polyurethanes (PUs). When he wanted to crush a tough rubbery PU into fine powder, the sample was placed in dry ice (to reach the glass transition temperature) & and it is moved at once into a pestle and mortar applying fast crushing. This needed repetition, on the same sample, few times until the powder was as desired.
Sometimes, he used to place a PU sample in liquid nitrogen & then he crushed it as above. I saw success in this way several times. It just needs some patience.
Thanks for all the answers. We used to grind our samples in Freeze/Mill (mechanical grinder), this is a cryomilling process using liquid nitrogen. But we have seen that after several cycles of milling the polymer films become non-transparent. We do not know yet if it is moisture or just rearrangement of the polymer chain and formation of crystallite structures. Thats why we wanted to do away with cryomilling. Instead looking for dry milling process where we can get very fine powders (~150 micron size).
I may not be able to recommend a specific method, but whatever you do, make sure it’s done at a temperature below the Tg of the polymer. From your description you are above Tg at ambient temperature.
I've ground harder cross-linked polymers in a mortar and pestle after drying it in an oven. This method was effective but time consuming. Have you tried a planetary ball mill at room temperature? That is the other way we are able to make very fine powders from our polymer.
We have tried ball mill but the particle size was not that low (not ~150 micron or less). Since the polymer is little gooey, it need to be rock solid by freezing it in liquid nitrogen.
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