As many of you may already know Precious Plastic initiative provides open-source designs for machines that grind, melt, and inject recycled plastic such as PP (plastic type 5) or PS (plastic type 6) mainly, allowing for the creation of new products from recycled plastic! [you can also search there for alternatives for other plastic types but there are not many]
See here: https://www.preciousplastic.com/solutions/machines/overview

Polyformer is another open-source project that aims at help solving world’s plastic waste problem. It is a 3D printed machine that turns plastic bottles which are made from PET (plastic type 1) into filaments for 3D printers. Check the PolyCutter before!
See videos here: https://www.youtube.com/@reitencheng4878
See more info here: https://www.reiten.design/polyformer

Check also the PET2print project!
See here: https://www.instructables.com/Turn-PET-Bottles-Into-3D-Printer-Filament/

Or the recycling PET plastic to filament project!
See here: https://www.instructables.com/Recycling-PET-Plastic-to-Filament/

Check out the amazing work of a group of students reported here: Prototype Pultrusion of Recycled Polyethylene Terephthalate Plastic Bottles into Filament for 3D Eco-Printing: Education for a Sustainable Development Project (2024)
See here: https://www.mdpi.com/2071-1050/16/19/8347
(ps: by reading it carefully you’ll find the Reciclator3D projects’ website (ES) and the machine drawings!)

Get inspired!