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Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
I need to powder some thermoplastics and wax-type materials (for example, microcrystaline wax, polycaprolactone aka "Shapelock", polylactic acid, etc you get the idea).
The smallest wax powder I've been able to get is ~20-30 mesh/600 micron but I'd like to reduce that by an order of magnitude. I also begged some 50-mesh/300 micron PCL out of an industrial supplier but it too is not fine enough.
I don't know if any of you have ever tried to grind a thermoplastic but its a disaster. In a burr grinder it goes goey and gums up the burrs in zero seconds. In an impeller-type grinder (like a coffee grinder) it amazingly just bounces off.
I understand that standard practice is to cool the stock with LN2 to embrittle it. Do you think dry ice would be cold enough to do the same? I figure perhaps I could mix up dry ice and my subject material and just run it through the grinder all at once, then allow the ice to sublimate....?
Is it the glass transition temperature that I need to get below? For PCL thats -60C which means that dry ice (sublimation -78.5C) should be OK...?
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
To get better thermal contact with dry ice, try a dry ice + alcohol bath. I have used one in the past when I need to chill things in a hurry (press fitting) and It's a lot cheaper then getting a dewar and some liquid nitrogen.
Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
For the record...
Pic #1 is my starting material - this is a "carvable" injection wax from Kerr Lab.
Pic #2 is one dixie cup worth of wax prills, plus one dixie cup worth of coarsely chopped dry ice, ground in a standard issue coffee grinder.
Pic #3 shows the result - the volume is greatly inflated by the dry ice, which will sublimate slowly over the next few hours.
Pic #4 shows that dry ice does NOT work with PLA/polylactic acid - despite the high glass transition temperature for this material it remains ungrindable even at dry ice temps.
So there you have it - at least for some wax, dry ice enabled the creation of a very fine powder.
Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
Carbon_Rod wrote ...
PLA is usually mixed with PDLA and or a 1/3 ratio cellulose composite... Kinda like the hotdog-meat of plastics...
Oh! That makes total sense.
I got my PLA in filament form for use in 3D printers. I had been wondering why the manufacturer recommended setting the extruder to 200C, given that I thought PLA melted at only 50 or 60C... must be the PDLA.
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Cryomilling wax/thermoplastic
