Hi Kenneth...
>Here's one for Y'all. Is there a safe way to remove paint from plastic,
>like a plastic jerry can? Could this be blasted with a media like walnut
>shells or sodium bicarb without too much damage? Any suggestions short of
>sending it out would be appreciated.
It depends on the plastic that the can is made of. Most of these
jerry cans are polyethylene (PE) or polypropylene (PP). If it is PE
or PP, you could safely use methylene chloride, which is the main
ingredient in most non-flamable paint removers (and also the liquid
sealed inside the glass tubes in Christmas bubble lights,
interestingly enough). If your cans are styrene (or any plastic in
the acrylic or styrenics families), methylene chloride and any other
solvent will dissolve the surface...if it is not PE or PP, you might
be able to use a citrus non-flamable stripper of some sort like the
non-flamable "Goof Off" product. You could always try naptha (white
camping gas stove fuel), but this could also attack certain types of
plastic.
Now, how do you tell what kind of plastic you have? Here is an
interesting excerpt from the USENET on how you can identify plastics
at home:
***
How To Identify Common Plastics
First, read the recycle code (see below for code numbers).
Alternatively, give it to the nearest IR spectroscopist who has a
polymer library.
But if you want some fun, try the following:
There are several simple tests that can be performed in the home that
can assist in separating common plastics, however it is important to
realize that formulated products contain large quantities of pigments,
plasticizers, and fillers that can dramatically alter the following
properties. If possible repeat the tests on a reference sample of the
plastic.
Visually examine the sample, looking for recycle codes. While you are
at it, you can check for indications of how the plastic was made -
molded, injected, rolled, machined etc.
Try assessing the flexibility by bending, and look at the bending zone
- does the material stretch or is it brittle?
Test the hardness, try scratching it with pencils of differing
hardness (B, HB, 1-6H) to ascertain which causes a scratch in the
plastic. Alternatively, attempt to scuff the sample with a fingernail.
Cut a small slither with a sharp knife. Does the sample cut cleanly
(thermoplastic), or does it crumble (thermosetting)?
Hold sample in small flame, note whether it burns, self-entinguishes
on removal from the flame, color of the flame, and smell/acrid nature
of fumes when flame is blown out (caution - the fumes are likely to be
toxic). Also attempt to press melted sample against a cold surface,
and pull away - does sample easily form long threads?
Drop the object or a sample onto a hard surface, does the sample
"ring" or "thud"?
Place the sample in water. Does it float, sink slowly, or sink
rapidly? If it sinks rapidly, it is likely to be halogenated (PVC,
Viton, PTFE).
If it sinks slowly, possibly nylon.
If it floats possibly polyethylene or polypropylene.
You could ascertain the actual density by adding measured volumes of
solvent until the sample neither rises nor sinks.
Now do the sliver test:
If cutting thin slivers results in powdery chips (thermosetting):
- carbolic smell in flame, self extinguishing, then it is phenol
formaldehyde.
- self extinguishing, black smoke, acrid, then it is epoxide (epoxy).
- fishy smell, then it is urea formaldehyde, or melamine formaldehyde
(urethane or polyurethane).
If cutting thin slivers results in smooth sliver (thermoplastic), and:
- metallic "ring", burns (styrene smell), then it is polystyrene
(note that high impact polystyrene may not give "ring").
- "thud", floats, hard, glossy surface, burns (paraffin wax smell),
then it is polypropylene.
- "thud", floats, medium-hard surface, burns (sealing wax smell),
then it is high density polyethylene.
- "thud", floats, soft surface, burns (paraffin wax smell), then it
is low density polyethylene.
- "thud", sinks, burns (fruity smell), then it is acrylic
(plexiglass).
- "thud", sinks, burns (burning paper smell), then it is cellulose
acetate or propionate.
- "thud", sinks, burns (rancid butter smell), then it is cellulose
acetate butyrate.
- "thud", sinks, difficult to ignite (greenish tinge), then it is
PVC.
- "thud", sinks, difficult to ignite (yellow color, formaldehyde
smell), then it is polyacetal.
- "thud", sinks, difficult to ignite (yellow color, weak smell),
draws into long threads, then it is Nylon.
- "thud", sinks, difficult to ignite (minimal flame, decomposition
but no charring, cellular structure forms, then it is polycarbonate
(Lexan).
30.2 What do the plastics recycling codes mean?
The recycle codes for plastics are as follows:
1 = PET
2 = High density polyethylene
3 = Vinyl
4 = Low density polyethylene
5 = Polypropylene
6 = Polystyrene
7 = Others, including multi layer
***
I'm sure the blasting method would result in fluffing of the surface,
so you should avoid that.
Good luck.
--Jim "Ike" Newton
o 1984 M1007 CUCV Military Suburban 6.2 Liter Turbo-Diesel Engine 5/4 Ton Cargo Capacity, 4WD
o 1971 M35A2 Military Troop/Cargo Truck "Deuce and a Half" 478 Cubic Inch Turbo-Diesel Multi-Fuel Engine Air Shift Front Axle 2 1/2 Ton Cargo Capacity, 6WD
See them at: http://www.CUCV.net
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