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Topic: Dangers of PVC exposed to high heat (lasers)?  (Read 611 times)

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Offline jasonronin

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Dangers of PVC exposed to high heat (lasers)?
« on: May 22, 2019, 10:52:45 PM »
Firstly my apologies that I am going to be a leech on the forum as I don't have a chemistry background so I can't help out, but I'm curious about a subject thats often brought up in the laser engraving community.

What happens if PVC is cut/engraved with a laser?

I've seen many, many people say "don't do it, its bad" and a few say "I've been doing it for years, its fine".

Those that say don't do it, say the high heat causes the chlorine to separate from the poly-vinyl, creating chlorine gas. Some leave it at that and say the chlorine gas is the threat. Other say the chlorine reacts with hydrogen in the air and created hydrochloric acid...then they state this will kill you. People often mention chlorine gas used to kill during the wars, stating this is the same thing.

I know dilute muriatic acid is sold in stores for cleaning, pool supplies, concrete neutralizer, etc and people use it often with no ill effects.

So what exactly is the threat/whats happening? Chlorine gas? Hydrochloric acid? The concentration of the hydrochloric? The atomization of it leading to increased chance of inhalation? etc.

If anyone is willing to give a breakdown of what happens, and what is the threat, it would be greatly appreciated. I will repost it on the laser forums to give people a more educated understanding of the issue.

Thank you for any help you can offer.

Online Borek

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Re: Dangers of PVC exposed to high heat (lasers)?
« Reply #1 on: May 23, 2019, 03:42:37 AM »
There are plenty of easy to google papers dealing with thermal decomposition/degradation of PVC, you can try them.

As far as I am aware it is mostly HCl that evolves. Yes, it is nasty (more because of being corrosive and giving burns than because of being a poison). At the same time it is hard to miss in the air, it is a strong irritant at relatively low concentrations, it will choke you and make your eyes itch.

Is it dangerous for engravers? Yes, and no. First, a lot depends on the amount of material removed. HCl makes about 60% of the products, vaporizing 1 g of PVC (that's a bit less than a cubic cm, my understanding is it is quite a lot for just engraving) will produce around 0.4 L of gas, which gets quickly diluted in the air. MSDS lists LC50 for mouse and rats in the 1000-3000 ppm range, 0.4 L of gas diluted even in a small, closed room means final concentration in the tens of ppm order, almost 100 times lower. Second, as far as I am aware laser engraving in any material without a good ventilation is a disaster waiting to happen, so a well designed working station should be probably safe even with PVC (although it will definitely speed up corrosion of metal elements in the ventilation duct).

(All possible disclaimers go here, treat what I wrote as an educated guess.)
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Offline Enthalpy

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Re: Dangers of PVC exposed to high heat (lasers)?
« Reply #2 on: May 23, 2019, 03:52:28 AM »
Most heated polymers are bad for health, and among them PVC is nasty.

Chlorine molecules and hydrogen chloride aren't the main concern. At heat, the atoms recombine, including with oxygen from the air, to create a vast spectrum of poisons. The monomer vinyl chloride is just one example:

More generally, chlorinated hydrocarbons are especially toxic in fires and at heat. Most compounds of C, H, Cl are poisons, and at high temperatures there is no control on what compounds are created. You get inevitably a very broad mix of compounds, many of which are toxic.

If you inhale the stinky fumes once you'll survive with temporary eyes irritation and a headache. But if you make a regular activity of it, without protection it will kill you. Have no doubt about it.

For my personal activity, I'd completely avoid heating PVC. If you really have to do so, and worse, on a regular basis, you need a fume hood that separates any living creature from the gasses and doesn't release the gasses in the atmosphere. Plus, comply with uneasy regulations.

My feeling is that choosing and installing the adequate equipment, defining its operation, is way outside your knowledge. To the very least, you need an expert, maybe the fume hood supplier, to define it for you, which won't make it cheaper. Even that way, when unexpected situations will occur, you won't make enlightened decisions, and this is dangerous.

Every polymer containing chlorine is equally bad at heat. The same holds for polymers containing fluorine, like PTFE and PVDF. Polymers containing nitrogen (ABS being common) aren't healthy to heat neither, as they can release things like acrolein and cyanide, even if in small amounts

Polymers containing only C, H and optionally O are less nasty at heat. These would be my preferred choice for laser engraving. It leaves you PE, PP, PET, POM and many more. Don't underestimate them neither.

Offline jasonronin

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Re: Dangers of PVC exposed to high heat (lasers)?
« Reply #3 on: May 23, 2019, 07:58:13 AM »
Thank you very much for the reply guys.

To clarify, I have no intention of doing it myself, even if only corrosion of the machine was the main concern. Luckily the designs I do, do not call for plastics. But I joined the laser forums about a year ago and at least once a week the PVC topic comes up.

The vast majority of these guys are hobbyists or small businesses that have not consulted with a professional when it comes to fumes...myself included. A typical setup is the laser in a box with an exhaust fan pumping the fumes outside...typically 10-20ft away. No fume scrubbers, etc in use. So while its not nearly as bad as being in an enclosed space, its definitely not ideal.

I wasn't sure if something like chemical pneumonia from HCL was the main threat or if there was something else at play like toxic build up in fatty tissue, hepatotoxicity, etc....its just not a subject I know anything about and was looking for more info than "its bad, don't do it".

Interesting that at high temps they will recombine into different, possibly unpredictable compounds, to me that sounds scarier than HCL fumes in small amounts.

Hopefully you guys don't mind if I point others to this post when the subject comes up.

(edit: I'll look up those papers on thermal degradation of pvc. Months ago I actually attempted looking for studies on lasering pvc but didn't come across any. The more general search of "thermal decomposition" should help me come across a few. Thanks.)

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