Identifying plastics?

WCraig

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Hi:

I got a box lot cheaply at an auction filled with what appears to be 4-5 types of plastics. How could I figure out better what I have? Couple of pictures follow:

IMG_2956.JPG IMG_2957.JPG

I have a little project where I think a couple of small pieces of UHMW would be ideal (low friction, easy machining). Would the whiter pieces in the middle of the second picture possibly be UHMW?

I wondered if I calculated weight per volume if that would help?

Thanks for any help,

Craig
 
MatWeb is a good source for information on various plastics. You will have a difficult time distinguishing various types of polyethylene by density alone.
I usually do a burn test as a first pass. Different plastics smell differently when I heat them with a soldering iron. Polyethylene and polypropylene have a candle wax odor to them. Nylon has a very distinctive odor, as does Delrin(acrylic). Acetone will attack PVC and ABS but not polypropylene, polyethylene, Nylon, or Delrin. Teflon os another fairly common plastic but there are several formulations. Teflon will resist the burn test.ro aq large extent. Hardness is another test that can help identify plastics.

To complicate matters, there are numerous plastic alloys as well as some exotic engineering plastics like Ultem and PEEK.

https://modernplastics.com/wp-content/uploads/2015/03/how-to-identify-plastics.pdf
 
I'll dig out a soldering gun and try those tests.
 
I chuckle - I was going to mention the burn-and-sniff as a joke :confused 3:

If you manage to get it alight, and it then begins to dissolve your eyeballs, and all the steel in your shop, you've got PTFE for certain!

ABS & PVC are super easy to tell by how they cut/smell with a hacksaw, but that doesn't help you. UHMW will act differently under a drill than Acetal. That black stuff I'd simply assume is Delrin, but that's just me I guess - except the shiny stuff (does it have a slight ring under impact? Acrylic).

The yellow color probably tells you more - it's either oil-mist adsorption, or UV degradation from fluorescent shop lights - if that's true that would rule out UHMW as far as I could say.

Also, abrasion. Who will scratch whom? How do the scratches appear? Strings or galling?

Start by cutting and cleaning a bit - just doing that will tell you a great deal about what you've got, just not specific formulation.

Anyways, I ain't your dad - and I do ill-advised dangerous things more often than I care to admit. Just... PTFE + flame = Hydrofluoric acid... and I try to avoid that particular ingredient... unless I'm enriching Uranium or something (that's a joke... Thorium is superior!!)
 
For some plastics you can purchase air welding sticks of known content. It is helpful to have a plastic of known content to compare with the characteristics of an unknown plastic especially if you are starting out for the first time.
 
As stated, examine toolmarks present, most appear sawn. Great clue to machinability. Thermoplastics melt, SOME suitable in only very low RPM applications. Some like PVC machine terrifically but don't have bearing qualities. Various Nylons and Delrins are good when mechanically applied. Each of those like honed HSS bits.
Thermosetting burns, some can be used mechanically. Phenolics with embedded linen eat HSS rather quickly...
 
For some plastics you can purchase air welding sticks of known content. It is helpful to have a plastic of known content to compare with the characteristics of an unknown plastic especially if you are starting out for the first time.

That is what I have done....and Hey @WCraig you are in Canada too!

Your local Princess Auto will have an assortment of plastic welding filler material:
https://www.princessauto.com/en/10-pc-polyethylene-plastic-welding-filler-rods/product/PA0008709982
https://www.princessauto.com/en/10-pc-abs-plastic-welding-filler-rods/product/PA0008699142
https://www.princessauto.com/en/10-pc-polypropylene-plastic-welding-filler-rods/product/PA0008709941
https://www.princessauto.com/en/10-pc-polystyrene-plastic-welding-filler-rods/product/PA0008710006

They are handy to have around, not only for plastic repairs, but can be used as known samples for comparisons.

-brino
 
@brino thanks very much for the links. I had the impression that I'd have to find a specialty plastics shop to get such things. I'll have a look at these the next time I'm at PA.

Craig
 
@brino thanks very much for the links. I had the impression that I'd have to find a specialty plastics shop to get such things. I'll have a look at these the next time I'm at PA.
You're Welcome!
They are in the isle with the soldering and welding accessories.
-brino
 
I am reviving this old thread that I found very useful! I have gone through my plastics box and identified most of what I have. Polypropylene/ethylene are pretty easy since they float in water. I also have nylon (characteristic smell with burning), abs, polycarbonate, acetal, and some PTFE.
I have a 3" section of round rod that is an unknown. For years I assumed it was nylon but this is incorrect. It is white and seems very dense. It does not burn or drip or make much odor. It is not soluble in acetone. It could be PTFE but it seems too dense and is not very slippery. I am at a loss on this one! Is there glass filled PTFE commonly around? What else is likely? I do not even know where I got this material. It is possible it came from Allegany Ballistics Laboratory so it could be uncommon.

Great Table:
 
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