From: knapp@spot.Colorado.EDU (David Knapp)
Subject: Re: Teflon: question about heating.
Organization: University of Colorado, Boulder
Date: Fri, 24 Jul 1992 05:04:11 GMT

In article <1992Jul22.221548.17086@yrloc.ipsa.reuter.COM> loc@yrloc.ipsa.reuter.COM (Leigh Clayton) writes:
> I'm not normally a reader of sci.chem, but this question came up in
>rec.food.veg a while ago and I hope someone here can lay it to rest. I will
>read sci.chem for a while so you can respond either by mail or a post; I'll
>summarise to rec.food.veg but not here unless people ask me to.
>
> I posted this article to sci.materials, and got one response suggesting
>that the gas Teflon *may* emit when heated too much is Phosgene.

The gas given off could as small as the CF2 monomer, or perhaps small chains of 
polymers as a soot or the monomer.

Phosgene is CCl2O or Carbonic dichloride. I don't see how that could be
a product unless you are cooking bleach or something ;-)


> The respondant
>was a bit cautious, though, since Phosgene seems to contain Chlorine and it
>isn't obvious where that would come from. Since the interest in rec.food.veg
>seems to still be there, I'm trying again this time to sci.chemistry; maybe
>we'll get better luck. I don't read sci.chemistry though, so if anyone does
>decide to post an answer, please post to rec.food.veg as well.
>
>       -----------Begin previously posted article--------------
>
> In article <1992Jun11.152827.4156@bb1t.monsanto.com> tjfeue@bb1t.monsanto.com
>(I think. He may have been responding to an earlier post) suggests that Teflon
>should not be overheated because it will emit a dangerous gas that will kill
>pet birds (and presumably people).


Teflon should *not* be overheated.  Beyond 400C it decomposes back into its
monomer, tetrafluoroethylene and beyond that, probably down to CF2.

In the Merck Index, it is only cited to cause mucous membrane irritation,
but hey, it could kill your birds...

> Teflon is (according to my American Heritage) a trade name for
>polytetrafluoroethylene. My organic chemistry is rather tentative, but I decode
>that name to look a bit like this:
>
>       F F F F F
>       | | | | |
>  ... -C-C-C-C-C ...
>       | | | | |
>       F F F F F
>
> This is sort of a chlorine-less, polymerised CFC. Containing Fluorine it
>clearly *could* be convinced to emit Fluorine gas, which is indeed very toxic
>(though why it would kill a pet bird and leave a human around to gripe about it
>is a bit of a mystery to me). But I would expect this compound to be quite
>heat-stable (and indeed, fluorine gas being well known to be so toxic I can't
>imagine regulatory agencies allowing anything likely to emit it in cooking
>utensils for home use). Of course, the indicted gas may not be fluorine, since
>there are lots of dangerous gases in the world (like cyanide, which is made out
>of just carbon and nitrogen, so there's likely some way to make it out of
>Teflon (or wood) and air too, but I'd be surprised to see a lot of it made just
>by heating the stuff too hot).

But you need to do some serious work to break the N2 bond to *make* that CN.

> This strikes me as a typical urban myth, but I'm cross-posting to the
>sci.materials group in the hope that someone there will know (or be willing to
>find out) exactly how thermally stable the stuff is.

It is not an urban myth. I have heated teflon in the lab and have encountered
the fumes. Have you ever gotten a whif of NO ( =>NO2 ) ? It's pretty rough
and, to my knowledge, can cause pulmonary edema the same way NO2 can.

As I remember, when we've ordered teflon samples, the book sized warning label
that comes with every order, included warnings about toxic gases  if overheated.
Personally, I'll take their word for it.  Merck does also say "..There 
have been reports of fume fever in humans exposed to unfinished products. 
Pyrolysis products are irritating to mucous membranes."

As far as birds go, yes, they are more sensitive to airborn toxins than humans.
This according to my brother who is an 'avian endocrinologist and reproductive
physigist', which certainly *sounds* good.  It has something to do with the
fact that birds respirate through the insides of their *wing* bones! 
(hey, this is just what I'm told)  You've certainly heard of a 'canary in 
a coal mine'. They didn't bring canaries into coal mines just to hear them
tweet, they brought them there because they made darn good toxic gas detectors.
Dead bird -> leave soon.


-- 
David Knapp                                      University of Colorado, Boulder
Highly Opinionated, Aging  and                      knapp@spot.colorad.edu
Perpetual Student of Chemistry and Physics.
            Write me for an argument on your favorite subject.