Laser cutting PET and PETG (is PETG really a banned material?)

#1

I noticed that the laser manual lumps polycarbonate and PETG together as the same banned material however I think this may be a typo. PETG is a glycol modified PET (“polyethylene terephthalate”) and is not related to polycarbonate. Anyone have input on this? If it’s wrong then I will edit it but want to check in to see what people say.

I thought maybe PET(G) could be banned for the same reason that polycarbonate is banned (that it absorbs the IR laser light and cuts inefficiently resulting in soot/flames), but the spectra I’m pulling up on the internet for PET(G) seem to show decent transmission in the IR. Also people on the internet appear to be cutting it with IR lasers.

Whether PET/PETG is approved at NB is a separate issue but first I want to make sure it’s not banned…

#2

It generates HCN when burned. https://www.jabil.com/content/dam/insights/data-sheet/jabil-petg-sds.pdf

It probably should note that at a minimum, maybe put it in with ABS below it’s current entry, as it lets off the same fume,

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#3

You can always talk to the guys at TAP Plastics about this. They’ve steered me away from bringing the wrong scrap back to Noisebridge a few times.

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#4

Cyanide, deadly, makes sense! Good call on MSDS I didn’t realize they had thermal decomposition/combustion data in those. I checked the MSDS for PET and it doesn’t list cyanide but somehow that glycol in PETG leads to cyanide.

Will make note for PETG in the wiki and try to investigate more on PET.

#5

It’s interesting that it makes cyanide when burned but has no nitrogen in it (cyanide is :C≡N:).

I guess it gets it from the nitrogen in the atmosphere.

I’d imagine it might be possible to rig-up the laser cutter to use dry Carbon Dioxide as the jet gas to prevent the C≡N from forming. This could also, in theory, allow a other problematic plastics to be cut because the laser would no longer be burning the material (no oxygen), it would be vaporizing it.

There’s still a possibility of icky decomposition products from pure thermal breakdown though, so not a guaranteed win. Research would be required.

What happens when you cut PVC on a normal laser cutter:

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