MineMan
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Mixing Thermoplastics, Equipment and Chemistry?
Hello All,
I have bought several types of plastic pellets, TPU, PLA, PETG and an extruder to make filament for my 3D printer. I want to mix these plastics in
various proportions to achieve a print with the ideal properties. For example according to a research paper I read the addition of TPU in PLA will
increase the elongation and the impact toughness; the resulting mix will act similar to PLA until 40% or more TPU is mixed in, then the mix will no
longer have any rigidity. When PLA is the majority, the TPU "droplets" are 4um in a matrix of PLA.
I bought a simple screw extruder hoping the two types of pellets could be added and extruded, but this is not enough, I need a way to pre process the
plastic, mixing them while molten with a capacity of at least .5L. I can't seem to find any equipment for this... maybe there is a specific name to
search for?? I envision a stainless steel pot, with a heater element and a motorized mixer.
The other option is to obtain the plastic in fine powder form instead of pellets, but again, I don't see availability of thermoplastic powders unless
in large quantities. I am up for grinding my pellets, but plastic is quite a hard material to powder... my only thought is to put the pellets in a
ethanol cooled by dry ice, take the pellets out, and blend... don't know if this will work.
Can anyone refer me to any types of small scale equipment or methods to mix molten plastic... Maybe a large sand bath??
Also, how can I tell if two types of thermoplastics are mixable by looking at their molecular structure, if they have a close melting
temperature, is it hydrogen bonding??
Search engines have really come to suck lately, with all of the Search Engine Optimization one can't seem to find specialty equipment or suppliers,
they are all over run with results that are only partially relevant by companies that pay the search engine, or optimize their website to show up
whenever thermoplastic is typed in... even is mostly irrelevant. SM might be the only hope for the internet!!
[Edited on 20-5-2018 by MineMan]
[Edited on 20-5-2018 by MineMan]
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elementcollector1
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What's the melting point of your TPU? Poly[urethane] has quite a surprising range of properties depending on its crystallinity. I'd imagine the %
crystallinity is quite low if your aim is to improve elongation, which would make the melting point and molten properties quite different from the
harder, more crystalline variety.
I'd imagine 4 um particles would be rather difficult to controllably synthesize in matrix in an amateur setting, but perhaps it's just how things work
out with this particular system. You may want to quote the paper's procedure and see if there's anything special about it.
Also, keep in mind that changing your plastic's properties will require an equivalent change in your printer's settings, unless that paper
specifies otherwise. 3D printer heads are extraordinarily finicky even with the 'approved' breeds of plastics, and you might want to plan for more
than one ruined extruder nozzle/setup.
Natural (no-additive, translucent) PLA's fairly brittle, at least compared to other plastics. Have you considered a coffee grinder, followed by ball
milling? In my experience, natural PLA behaves fairly rigidly and should powder well under these conditions. Failing that, I'd imagine a stovetop, a
'sacrificial' pan or pot and some vigorous stirring of the molten PLA should get you somewhere, at least in terms of mixing. You might also burn some,
but it's a worthy sacrifice if you produce enough workable-quality material.
Generally, plastics are never quite 'mixable' - one of the fundamental problems in macromolecular engineering is that all save for a few select blends
will refuse to dissolve in one another. Entropy's a tricky beast at the best of times. However, since your end goal seems to be a suspension
rather than a dissolution, you should be fine with just physical mixing.
[Edited on 5/20/2018 by elementcollector1]
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Twospoons
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How about making a cutter to sit at the end of your extruder, turning filament back into pellets. That way you could keep reprocessing your plastic
until you are happy with the mixing.
Helicopter: "helico" -> spiral, "pter" -> with wings
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unionised
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Are people assuming that all polymers will mix?
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aga
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Get a tuna tin, chuck in some of each pellet.
Stick a candle underneath, light it, then start stirring the pellets.
If they melt and mix, they are 'mixable'.
Gonna be hard to achieve a constant 1.75mm diameter filament for running thru a standard 3D printer.
I'd suggest getting that part right before wasting effort on the mixing thing.
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