It is called "pultrusion". A key property of PET plastic is that it is not infinitely re-meltable, it gets more brittle each time. If you melt bottles to form filament, then melt it again when printing, those two re-melts are too much.
But, you can heat it enough to soften it without truly melting it -- so it does not loose strength -- and pull it through a heated nozzle, that kind of wraps the little strip around into a tube, sometimes with a small hollow center like a straw.
There is then one full melt left in the plastic's life to allow a 3D printing.
You might have to adjust for the filament being hollow and extrude a bit more.
You also get a filament with a shorter length, just the plastic from one bottle, because joining the filaments is finicky and no one seems to have come up with a reliable way yet.
In spite of all this, it's really appealing because getting one more human use out of the vast volume of PET bottles that are thrown away seems really useful.
Note, that the strips that you cut the bottles into, are useful by themselves. There are a series of youtube videos by a Russian guy building a log cabin in the woods, and he utilizes those strips extensively -- if you use them to tie things together, you can pour hot water on them or heat them with a flame and they will shrink and stick to themselves, making a really strong joint.
>it's really appealing because getting one more human use out of the vast volume of PET bottles that are thrown away seems really useful.
So where are all our old plastic bottles? Mostly, we're wearing them.
So sure, we get one more use out of that clothing, and then it gets put in a landfill or "donated" to west African countries that receive a year's supply of clothing every week.
I searched youtube and found a youtube short of it being used.
First you have to use another small machine to slice up a plastic bottle into a spool of roughly formed plastic spaghetti. Then you feed it through the nozzle on this machine to draw it into a properly formed filament.
Having to slice up every plastic bottle you want to run through it by hand seems like a cost to using it in any kind of bulk (I originally was trying to work out if it melted them down which would alleviate that).
The Recreator3D[2] somewhat automates the bottle cutting, feeding, and filament making. Older versions repurpose a specific 3D printer's hardware, but the MK6[3] uses largely off-the-shelf parts.
Igor Tylman sells kit and fully-assembled PETmachines that cut, feed, and pullstrude filament.[4]
1: http://PPU3D.com, which just redirects to https://www.facebook.com/groups/petpultrudersunited
3: https://www.printables.com/model/352729-the-recreator-3d-mk6...
4: https://www.etsy.com/listing/1851116187/petmachine-fully-ass... with a pretty thorough demonstration at https://www.youtube.com/watch?v=WUcZyOWUzcY
One thing to consider is that PET isn't the same as PETG, and may require changes when printing, and possibly additional ventilation
https://all3dp.com/2/pet-vs-petg-differences-simply-explaine...
Also from the link (I just thought it was a little funny and answered a question I had)
> "Do all plastic bottles work?
Yes, as long as the bottle is made of PET. But the bigger the bottle the more filament can be made per bottle! Plus don’t forget, any colour of bottle will work!
If I lose 10 cents by turning a 500 ml bottle into filament, will I get at least 10 cents worth of filament out of it?