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Chemically grinding ABS scrap: part 2Thursday, December 11. 2008
In which your narrator continues his efforts to get something for Adrian to
put in his granule extruder...
This time I prepared 5 cm^3 of ABS from 3 mm filament by cutting it into
4-5 mm bits
To this I added 20 cm^3 of pure acetone at room temperature (~18-20 degrees C).  After about an hour with periodic stirring to keep the softening bits from sticking to the bottom of the container about 20-30% of the ABS was dissolved. At that point I put the jar in a water bath 43 degrees C. (~110 F).
Raising the solvent temperature allowed the rest of the ABS to dissolve within
another 20 minutes. Thus, at this point, I know that I can dissolve ABS in pure
acetone in volumetric proportions of 1:4. I expect that it would be possible to
improve on this. The limiting factor seems to be the need to wet the pieces of
ABS with acetone more than anything.
When I decanted the ABS dissolved in acetone in the previous experiments I
skimmed the floating precepitate off the water and was able to filter it quite
easily with an ordinary coffee filter. Unfortunately, I soon discovered that
much and possibly most of the precipitate was heavier than water and settled,
over a period of days to the bottom of the water.
As a result of that, this time I simply filtered the whole water/acetone
mix through the coffee filter so as to get all of the ABS precipitate instead of
just the lighter fraction. While the light fraction of ABS did not jam the
coffee filter, apparently the heavier fraction was of a fine enough grain size
that it did and I had extreme difficulty using the filter to separate water and
ABS precipitate.
Cleaning the filter several times and changing it once did allow me to
recover all of the precipitate eventually. I know now, however, that coffee
filters aren't going to be a practical way of recovering the ABS. I'm beginning
to think that some minaturised variation on a spray drier is going to be needed
in which we can skip the need to precipitate the ABS in water.
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If you want an efficient way to remove particulates from a fluid... hydro-cyclones are a good option. They are small and highly efficient at separating very fine particles from liquids. the only moving parts are in the pump that feeds the hydro-cyclone.
Spray drying tends to need very high temperature air in order to minimize the size of the drying chamber (cooler air needs more contact time with the droplets). You also need to atomize the solid/liquid suspension, which adds to the complexity of the apparatus.
When using a spray-dryer you generally need a air-cyclone to catch the product... if you're making a cyclone, you may as well make one that works in the liquid rather than gas phase. Saves the energy associated with evaporating the liquid.
Super! Got some links so I can see how they work? Have we got patent issues with this method?
http://en.wikipedia.org/wiki/Cyclonic_separation
Just like a Dyson Vacuum cleaner. They're also commonly used in wood shops to separate out the bulk of wood chips / sawdust before a second stage of (more expensive and labor-intensive) bagged filtration.
Patent issues... I don't think so. The design methodology is set out in Perry's Chemical Engineers Handbook, and it is standard equipment in process plants such as paper mills, oil drilling platforms and many others. Dyson have patent on the use of cyclones in a particular configuration for domestic vacuum cleaners. They don't have patent on the concept of cyclonic separators.
That's good to hear. I'm hoping that somebody else takes that task on. I'd like to get back to work on my printable variable reluctance linear stepper motor. I'm also going to be trying to see if I can control warping with HDPE using a hair drier like Adrian just blogged. If we can crack the problem with warping on HDPE we effectively cut the filament cost in half.
Could this acetone/ABS solution be used to print ABS with a printer cartridge? As in, does the ABS dissolve sufficiently to be used like ink in a printer and then print subsequent layers at very high resolution?
It seems like the acetone would evaporate once the print was completed, so that the residue would be all that is left behind.
Possibly, this would require the chamber to be heated in some way to facilitate the joining of new material to already printed layers.
Just a thought.
Interesting idea! I hadn't considered that. Mind, you'd be getting a lot of acetone evaporating, but really not that much. Fascinating! I'm really going to have to give that some thought.
Great discussion, is there more on this in a previous thread? Also, here is what I know about ABS from working for a short time at Formall Plastics in Knoxville, TN years ago.
We used Trimethylethylene (spelling) or Dimethylchloride to make glue using the ABS regrind. It dissolved quite readily. I don't see why you couldn't dilute it to a very thin liquid. I have no clue about the Environmental impact on humans or Earth.
I tried to memorize the names of these chemicals because I thought it would come in handy for molding things. Please, let me know what results you get with them. Oh, and they are probably very flammable, but I'm only guessing. This was in 1975, so who knows if they are even available or EPA approved anymore.
Michael Couch
1. That would be much easier to dissolve the ABS if you first grind it mechanicaly to the maximum state you can obtain, and then dissolve it in acetone. Also, acetone gets crazy if it's warmed. You just shall care about acetone gas with air, which can easily detonate.
2. Printing with such liquid would be much better than using thermal way. Liquid could be thrown to the surface at evaporation point, so it will immediately make firm.
3. Maybe old dot-matrix printer printhead could be used.
4. Looks like you can use any dissolvable plastic this way.
ps i'd be glad to get comments for my grammatics =)
1. The point of using acetone was to avoid having to grind plastic. 2. I certainly hope you are right. 3. Possibly. 4. Yes. (ps) {That would be much easier... - It would be much easier} {You just shall care about acetone gas - You should be careful with acetone vapor} {Printing such liquid - Printing such a liquid} {so it will immediately make firm - so it will immediately solidify} {Maybe old dot-matrix - Maybe an old dot-matrix} {for my grammatics - about my grammar} :-)
Whoops =) That must be quite difficult to do. ABS has irregular structure. That means there's infinite quantity of different polymere molecules. Some of them are well dissolvable in acetone, some are not. That's why solution has that milky color.
Maybe something like chemical separator could help. At least you won't have to shake that box =)
ps my English is soooo bad...
"my English is soooo bad... " Not at all. Your posting was perfectly comprehensible which in English is what really counts. You asked for comments on your grammer, so I tried to help. I had no trouble understanding what you were trying to say.
How important is it to have powder? Could you live with fibers? If so, you should try electrospinning, where you put the acetone-ABS solution in a syringe, apply high-voltage to the needle and aim it at a oppositely charged plate. http://en.wikipedia.org/wiki/Electrospinning
Getting the acetone back might be a problem though...
If you put high voltage electricity through acetone vapour say goodbye to thine eyebrows. :-s
I was just wondering if you could make shot instead of powder. Would a shot tower or Bliemeister process work for ABS?
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