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Old 30th April 2019, 02:34 AM   #101
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by gingertube View Post
I'm wondering if earlier poster confused PTFE and PVC and got them backward with respect to which can be hazardous at higher temperatures and which is not.
With respect, you need disentangle normal out-gassing (or simply getting over 70C with PVC) from pyrolysis and combustion products.

PTFE starts decomposing around 250C and the results are toxic, in varying degrees, starting with teflon flu. PVC also produces nasty, toxic compounds when burnt (e.g. HCL & dioxins).

So keeping away from melting or smoldering cables is a very good idea, regardless of what the insulation is made of.

LSZH cabling is less lethal but breathing the fumes is still not recommended.

General soldering at the level we do is unlikely to cause serious issues.
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Old 30th April 2019, 06:25 AM   #102
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by gingertube View Post
I'm wondering if earlier poster confused PTFE and PVC and got them backward with respect to which can be hazardous at higher temperatures and which is not.
No, I did not.

I was first introduced to PTFE insulated wire around 1990, while working in a university physics research lab. The wire was used in electronics that went into high-vacuum chambers. Just like your laser use case, it was necessary that the insulation be relatively resistant to outgassing - at room temperature.

When soldering the wire (with the usual 60/40 lead/tin solder), I noticed that it emitted a very nasty stench that made me cough. Clearly, the soldering process was heating the PTFE insulation sufficiently for it to break down and emit something noxious.

You may very well be right that PVC is also nasty toxic stuff - but so is Teflon, at the temperatures at which we normally solder electronics (and, as you will see, at considerably lower temperatures as well.)

If you think Teflon is safe at soldering temperatures, please read this: Teflon offgas studies | Canaries in the Kitchen | EWG

That link comes with a long list of references, proper peer-reviewed scientific publications. Here are some excerpts:
Quote:
thermal degradation of Teflon leads to the slow breakdown of the fluorinated polymer and the generation of a litany of toxic fumes
<snip>
At least four of these gases are extremely toxic
<snip>
...PFIB, which is a chemical warfare agent 10 times more toxic than phosgene

<snip>
Many of the thermal degradation products are unmatched in their environmental persistence.
<snip>
The lowest temperature at which nonstick coatings have been reported to kill birds in a peer-reviewed study is 396F (202C) [3].
<snip>
...recorded 52 percent mortality in 2400 chicks within three days of the birds being placed into floor pens with new PTFE-coated heat lamp bulbs.
<snip>
...Teflon offgases toxic substances at temperatures as low as 396F and 325F.
<snip>
...fumes generated at temperatures below 572F (300C) are formed exclusively by sublimation of a low MW (molecular weight) fraction already present in the polymer.
<snip>
...at low temperatures PTFE offgases particulate matter which is composed of small molecules of PTFE...this particulate matter...has been reported to cause bird deaths at temperatures below 500F (260C)
<snip>
Within four hours of exposure to a Teflon-coated pan heated to 536F (280C) parakeets died, and quail were killed when the pan was heated to 626F or 330C
<snip>
The facts are clear: PTFE is NOT your friend.

I set my soldering iron to either 700 degrees (F), or 750 deg F, depending on the size of the object to be soldered. Some of the studies cited in the above link show that PTFE outgasses sufficient toxic fumes to kill birds starting at temperatures as low as 396 F, far, far below the temperature at which normal through-hole soldering is done.

Even SMD parts are typically soldered with an iron set to 600 - 650 F, which is also well above the 396 degree threshold above which PTFE emits enough toxic fumes to kill birds.


-Gnobuddy
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