Recycling/reusing plastic

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Old 12-02-17, 10:40 PM
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Recycling/reusing plastic

Most of us have seen (or tried) an organic solvent such as acetone or MEK used to dissolve styrofoam packing. Have any tried to use the goo resulting from this experiment?

A couple of years ago I melted down some packing with MEK and then got the bright idea to use it in filling the steering wheel hub of my lawn tractor project. It seemed to work well. A couple of weeks ago I tried melting ABS filament (for a 3-D printer) into MEK and then used the goo to fill some cuts in a larger piece of ABS plastic. Again, it seemed to work well. In both these latter applications I applied the goo in rather thin layers and allowed it to set overnight.

So then I got the bright idea of using the goo to fill in the bottom of the lawn tractor chassis before I painted it. This would have filled in many cuts and molded depressions from the original stamping as well as dressing up the subsequent welds that I have made. So I poured some of my remaining MEK into a juice can and proceeded to add some packing peanuts. First thing I discovered is that not all packing peanuts are styrofoam.

It seems that the box of peanuts I had been saving for this project are NOT polystyrene at all but some other kind of soft flexible plastic. The MEK had almost no effect on it. So I fished those pieces out and just used what looked like PS foam and that melted okay. I tossed in a bit of ABS pipe cement for good measure and kept adding foam and mixing until I got a good thick mixture. I poured this into one of the cavities and let it self-level. Looking at at it a while later I could see it had "skinned over" but the surface would periodically display waves across it which would then subside and later reappear. It was cool but I wondered if it meant the surface was hardening by solvent evaporation while the mass of the goo had the solvent trapped. For this reason I didn't lay it on too thickly.

Well, I left it alone for a few days and it seemed to harden throughout and was well bonded to the steel in most places. Unfortunately it was not bonded in the thinner areas where I was able to peel it right off the steel with no problem. So then I decided it needed to be of a minimum thickness but not so thick as to prevent total solvent evaporation. I mixed up some more goo and layered it on fairly thick, maybe a scant 1/4 inch in places.

Two days later and I checked and found it was NOT hardening under the surface. In fact, I could take a putty scraper and dig most of it out right down to clean metal. And yes, there WAS still a lot of solvent stink with it. Amazingly, or maybe not, it also softened the original layer that I thought had bonded and hardened well. I proceeded to dig out what I could of this failed experiment. Now I have to go back and clean everything up and start over. I was thinking of using casting resin but maybe I'll just use Bondo autobody filler instead.

Bottom line, while recycling of styrofoam (and other packing materials) MAY be feasible, unless you have a chemical background and KNOW what materials to use with what solvent and where to use the resultant plastic...it's probably not a good idea to experiment.
 
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Old 12-03-17, 02:27 AM
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But trial and error is how a lot of us learn stuff
 
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Old 12-03-17, 05:26 AM
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Did this in high school as an accident / turned personal experiment... dissolved an entire box of Styrofoam peanuts into a 1000mL beaker of acetone. It formed a precipitate on the bottom, and after i left the acetone evaporate, the precipitate eventually hardened to form an opaque plastic "hockey puck "... felt similar to the plastic used to make milk jugs... very light.

Some Styrofoam peanuts are made from corn starch and dissolve in water... not sure what would happen to them in acetone. Probably a gooey mess.
 
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Old 12-03-17, 06:23 AM
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Long before they came out with 20' bee spray, a rite of passage for apprentice painters was being told to take a styrofoam coffee cup, fill it have full with mineral spirits and throw it on a bee's nest. Of course the thinner would eat thru the cup before you got 5' from the truck.
 
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Old 12-05-17, 03:26 AM
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Mark, my younger brother (RIP) told me they did this in his high school wood shop only they used lacquer thinner instead of mineral spirits. I may be wrong but I don't think that mineral spirits is "hot" enough to dissolve a styrofoam cup all that quickly.

Another memory is when I was in fourth grade there was a kid that had a bottle cap with a horse head on top. As I recall it looked like a chess knight as it was an armored horse. I wanted that stupid thing soooo bad I went home at lunch and begged my mother for a nickel or dime or whatever so I could buy it. Well, it had paint on the thing and I thought I would remove the paint by soaking it in a can of thinner. Next day I tried to fish it out of the thinner but couldn't so I poured out the thinner and all I found was the cap by itself.

Next experiment: Since I have a ton of the old 100% solids epoxy coating I've mentioned a few times I decided to mix some up tonight and see if a thick layer, something an inch or so thick, will cure solidly throughout in a week or so. Previous experiments with the paint have shown it takes several days of curing before it will no longer show fingerprints and at least a week before it seems hard. However, once it has hardened it has been quite hard.
 
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Old 12-05-17, 04:03 AM
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I may be wrong but I don't think that mineral spirits is "hot" enough to dissolve a styrofoam cup all that quickly.
Mineral spirits doesn't dissolve the bottom of a styrofoam cup instantly, it takes a minute or so .... but it is quick enough that the victim never makes it far from the truck before the bottom of the cup falls out.
 
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Old 12-08-17, 12:19 AM
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Good news!

I mixed up some of my 100% solids epoxy coating and poured it into a small paper cup. The purpose is to see if it hardens throughout in thick layers. I have it about 1-1/2 inches thick and after about 72 hours it is getting rather hard. I can't dent it with a finger but I can use a paint can lid lifter to put a small dent in the side, yesterday I could put a large dent in it.

I also poured out some about 1/8 to 1/4 inch thick and it is hard today. Yesterday it would still accept fingerprints or some shaping by hand.

The original instructions stated to mix two parts of the A component with one part of the B component; I probably mixed about 1-1/2 parts A to 1 part B this time. The garage has been at an average temperature of about 43 degrees and 75% relative humidity. Next step is to wait another 24 hours or so and then cut the glob in half to see if it hardened in the middle. If so, then on to the next step where I will clean all the dirt and grease off the back half of the undercarriage of my lawn tractor project and then mix a goodly amount of the epoxy and pour it into the bottom of the chassis.
 
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