r/plastic

Hello there,

I stumbled upon this paragraph and it left me a bit confused, since my basic chemistry knowledge taught me otherwise.

>The G in the acronym PETG stands for Glycol which is added during the manufacturing process. Glycol modifies the properties of PET [...]

https://prusament.com/materials/prusament-petg/

To my understanding, the "G" in PETG does not simply stand for glycol, as is often claimed (and not just by Prusa). As confusing as this may sound, the "E" already stands for glycol - while the “G” actually stands for "glycol-modified copolyester" (and not "contains glycol").

Stick with me for a moment and let's start simple with good old PET.

PET stands for Poly Ethylene Terephthalate. It is produced from the monomers ethylene glycol and terephthalic acid (or dimethyl terephthalate). So the "E" effectively refers to ethylene glycol (also called monoethylene glycol or MEG). Since the common name for this substance is simply "glycol", the "E" already indirectly represents glycol. Chemists may also refer to the broader family of MEG-derived compounds collectively as "glycols".

Now to PETG. The common explanation is that glycol is "added during the manufacturing process". But that is not really what happens. Instead, part of the ethylene glycol is replaced with another diol - most commonly CHDM (cyclohexanedimethanol).

If the ratio of MEG to CHDM shifts further toward CHDM, the polymer may then be classified as PCTG, which some people might know as the "bigger, stronger brother" of PETG.

And finally, if the ethylene glycol were entirely replaced by CHDM, the result would essentially be PCT, yet another polyester.

Since I’m not a chemist, I’d genuinely appreciate feedback from someone with an actual background in polymer science to shed some more light on this - and, of course, correct me if I'm wrong.

TL;DR:

PCTG is a modified version of PCT with partially added (ethylene) glycol - but PETG is a modified version of PET with partially replaced (ethylene) glycol (or respectively, the G stands for "modified by an additional glycol / diol component").

Am i wrong?

Hey everyone,

Some of you might remember a post I made a while back showing off a custom MagSafe wireless charger I designed and 3D printed for the E46 centre console.

Since that worked out so well, I want to use my mechanical engineering background and print setup to try tackling more of the infamous E46 "plastic-itis". We all know how brittle the plastics and clips get on these cars after 20+ years in the Aussie sun.

I’m looking to model up and print some of those annoying little parts that are either NLA or cost stupid money to ship from overseas just for a 50-cent piece of plastic. I'm already looking at redesigning the window regulator sliders and those interior trim clips that always break, but I want to know what else is driving everyone crazy.

Is there a specific bracket, trim piece, or sensor clip that always snaps on your car? Or maybe another custom quality-of-life mod you wish existed but no one makes?

Let me know what’s currently giving you grief. Also, if anyone has their broken original pieces sitting in a bin somewhere, let me know—I'd love to grab them to get the dimensions right!

Hi everyone,

I’ve nearly completed the full restoration of my ‘67 Mustang, but I still need a headliner.

I wanted to make my own hard removable headliner, just like the fiberglass ones that CJ pony sells.

I was able to generate a concept image, where the headliner would be made from some ‘frosted’ looking black plastic to diffuse the LEDs that I would sandwich between the ceiling and headliner.

I’ve been struggling with picking a plastic though.

It needs to be easily moldable and not sag after a few summer parking lot heat cycles.

Any suggestions? I’ve been told I’m looking for a unicorn.

I was planning on draping the sheet of plastic over a mold of the ceiling and forming it with either a space heater or heat gun, but maybe I should just get a dedicated plastic oven to evenly heat it?

Any advice is appreciated!

Cheers

Context: I'm trying to repair a couple boomboxes but a couple of them have broken pieces. The first one has a little black catch and the second one has some more obvious bits. Trouble is different types require different glues.

Note that the black crap on the second one was from some plastic molding kit someone recommended but it doesn't stay malleable long enough and it also doesn't do a good enough job affixing the two sides of the break back together so I abandoned that endeavor.

I've tried looking online and on Reddit but I can't find any details listed; what type of plastic is this? Also any information on commonly used plastic types in boomboxes in general would be amazing since I would love to learn more and do a better job of understanding the materials used and how to best work with them.

I took of a rubber part of an old Roland VDrums kit to repair it, I cleaned it and left it in sun, and it litterally melt liquide in an afternoon. What plastic could it be made of ?

Currently working on a soft serve truck. I'm trying to avoid tempered glass because of possible shattering. Of course I want a clean look with this type of display. Are there any films or clear tints that I can put over poly that would significantly change the scratch sensitivity? Any recommendations other than poly?

I bought a phone case from Ali***ress for my phone and only now realized that the rear insert is not actually magnetic. I already checked it with a multimeter set to resistance (ohms) and confirmed that the part is metallic. I'd like to remove this metal insert and replace it with a truly magnetic one. I already tried mechanical prying with a blade but only ended up damaging the surrounding plastic housing.
Which solvents or debonding agents could be used to detach this metal component from the plastic substrate? Unfortunately there're no identification marks on the plastic, so I cannot determine whether it is ABS, PC, TPU, or another thermoplastic.