I have looked into this a bit, and I find making things with 3d printers is pretty slow compared to using a mold. 3d printers are great for making original patterns, but not so great for making durable parts from plastic especially when your plastic is not consistent in quality.
I believe the right way of doing this, is use a resin 3d printer to make silicon molds, then use the recycled plastic in these molds via injection molding.
Or, buy molds and then inject.
This video demonstrates one such method of using recycled plastics in injection molding.
I would be interested in your experience with this if you have done this and if you have photo's of your setup.
I adore Linux, and love open sourced ideas...
Mart