Re: [ATM] Help with identifying plastics

[Mark Holm <mdholm@telerama.com>]

In a reasonably well equipped lab, there are a number of fairly simple
tests that can narrow it down fairly well.  Melting point, density (for
an unfilled material, solubility in a few different solvents.  At home,
or in a shop, it is more difficult.  If I still worked in a plastics
lab, I would just suggest you send me a piece and I could do the ID on
the side.  Unfortunately, though I am still working with plastics, it is
 now on the engineering side rather than the chemical side.  I don't
have my trusty IR spectrometer and DSC at hand.

There are also some flame tests that can be diagnostic in certain cases.
 The only one that doesn't require a reference sample, or prior
experience, is the copper wire flame test for chlorine.  Get a fairly
hefty solid copper wire.  Heat the end till it glows in a propane or
methane flame.  Touch the hot end to the material, then put it back into
the flame.  If chlorine is present, you will see a flash of green in the
flame.  The most common chlorine containing plastic is Polyvinyl
chloride (PVC).  There are others, and some non chlorine containing
plastics have chlorine containing additives to improve flame resistance.
 This test is so useful, I used to do it at least once a week on unknown
materials.

Check if a small sample floats on water.  A lot of plastics have
densities lower than water, but some quite common ones, including PVC
are denser than water.  If it isn't filled or pigmented, appearance can
be helpful: transparent, translucent, opaque.

Pigmented and filled materials are a pain.  Can't judge their optical
properties and it is hard to get a thin film you can put enough IR
through for a spectrum.

Give some indication of stiffness and brittlness.  Stiff and brittle?
Soft and ductile?  Sort of in the middle?  How about texture? Slippery,
not so slippery.  Break a piece and look at the fracture surface.  Do
you see glass fibers sticking out?  That is glass filled.  Do you see a
slightly rough surface with lots of shiny facets? Mica filled.  Did it
break cleanly? That is a brittle material.  Are there regions of
stretched out material?  That is more ductile.

-- 
Mark Holm
mdholm@telerama.com

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