PET-G Thermoforming and Heat Treatment Safety
 
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PET-G Thermoforming and Heat Treatment Safety  

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weHavetheMeats
(@wehavethemeats)
New Member
PET-G Thermoforming and Heat Treatment Safety

I am not sure if this is the correct place to post this, so if there is somewhere more appropriate please let me know. I am planning on using PET-G in a project similar to this 3D printed arm brace. https://www.instructables.com/3D-Pri...ization-Brace/ The manufacturing process involves submerging the 3D printed part into a pot of boiling water to heat the plastic to its glass transition temperature, then molding it around an object like a person's forearm so that as the part cools it accurately conforms to the arm's dimensions. After that I want to use my oven to heat treat the PET-G to improve its impact resistance. Before doing any of this, I want to ensure this process won't release any harmful vapors or carcinogens during manufacturing. I know PET-G is safe to print without ventilation and is considered food safe. However, is PET-G safe to thermoform and heat treat? Thank you for your help in advance.

Posted : 20/04/2021 4:40 am
Dan Rogers
(@dan-rogers)
Noble Member
RE: PET-G Thermoforming and Heat Treatment Safety

PETG won't out gas at the glass transition temp (around 200 --> 250 c, depending on the composition).  I don't think boiling water is going to soften PETG, it is only 100 C.

A 450 degree oven will do it.

 

Posted : 21/04/2021 7:14 pm
Neophyl
(@neophyl)
Famed Member
RE: PET-G Thermoforming and Heat Treatment Safety

Glass transition temp for petg starts at around 75c depending on brand and from the Prusa article on annealing they reckon 90-110c is a suitable temp so boiling water is right in the sweet spot.  Pretty rough on whoever's arm you are using though 🙂 

You are safe on the outgassing.  If you have printed it already then heating it up to annealing temps isn't going to do much at all.

Posted : 21/04/2021 7:38 pm
Dan Rogers
(@dan-rogers)
Noble Member
RE: PET-G Thermoforming and Heat Treatment Safety

@neophyl

I did not know that you can't put PETG in the dishwasher (70c) - I do that all the time - and it doesn't soften or melt.  Maybe I don't understand the term glass transition.  I assumed it meant melting point.

Posted : 21/04/2021 7:54 pm
Diem
 Diem
(@diem)
Noble Member
RE: PET-G Thermoforming and Heat Treatment Safety

The manufacturing process involves submerging the 3D printed part into a pot of boiling water to heat the plastic to its glass transition temperature, then molding it around an object like a person's forearm so that as the part cools it accurately conforms to the arm's dimensions.

PETG won't mould unless at temperatures that are likely to cause burns/scalds.  Is it possible to take a cold mould and make a cast of the arm to mould around?  Or work with PLA, scan the tailored PLA and reprint the scan in PETG?

After that I want to use my oven to heat treat the PET-G to improve its impact resistance.

PETG is not going to gain much from annealing, better to design a stronger shape or a thicker part.

Before doing any of this, I want to ensure this process won't release any harmful vapors or carcinogens during manufacturing.

Natural/clear PETG will be fine.  Colours might cause problems unless you can identify the pigments and get safety data on them.

Another possibility is to make a strong outer scaffold and join it to a tough, mouldable liner; it would be worth experimenting with TPU Flex.

What are you designing?

Cheerio,

 

Posted : 21/04/2021 8:17 pm
Neophyl
(@neophyl)
Famed Member
RE: PET-G Thermoforming and Heat Treatment Safety

@dan-rogers

Glass transition temp is when it becomes soft but not at the melting point.  Prusa did an article on annealing here that also explains GTP  https://blog.prusaprinters.org/how-to-improve-your-3d-prints-with-annealing_31088/#:~:text=PETG%20was%20annealed%20at%20110,a%20tougher%2C%20heat%20resistant%20extruder.    but CNC Kitchen also did at least one video about it previously that was quite interesting.

Posted : 21/04/2021 9:12 pm
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