Recycling Plastic Bags


We’re a group of students in Barcelona building the machines with the help of Fab Lab Barcelona. Tomas, the director of the Fab Lab, is really excited about the project because he is in contact with the Green School in Bali where they would love to use the machines to address the problem of plastic bags in Bali.

Now it seems that shredding the plastic bags in the shredder might be a little complicated. Since plastic bags are very thin and thus very ‘plastic’ (obviously), some plastic might get stuck in between the parts and I imagine in general it wouldn’t get shredded very efficiently.

Does anyone have any ideas on how to solve this problem in an easily implementable way?

Maybe it is not necessary to shred the bags add all and we can insert them directly in the machines in order to melt them and compress them inside the machine (at least for the injector and the compressor).

Or the bags should be melted together and then cooled down again in order to form thicker parts that can be shredder more easily in the shredder. Ideas include heating them with a hair drier or dropping them in hot oil,…

If you have any suggestions or ideas, please share them!

Thanks a lot!



Hi. When you are working with thin sheets you need an additional process. Just milling isn’t enough. you need to make little balls from plastic first.

Plastic bags have a different recycling process it’s called agglomeration, since plastic bags are so thin and light weighted they can’t be fed into a hopper as bulkier plastics, that’s why you need to use a machine called Plastic Densifier or Plastic Agglomerator. It’s not a complicated process and the machines needed are really easy to make (here in Venezuela most of them are homemade), a set of blades spin at high speed at the bottom of a metal drum, plastic bag will be cut and due to the heat of the process they would regroup into a heavier form that requires less space and handles better in processing, I’ll add some photos at the bottom.

You are not the only one, check out these topics 😉



I think the best way of recycling the bags, is tho shred directly in a bag, or directly to extruction machine, for example, you combine those two machines one over the other, ehe shredder over the extrusion, and, on the output of the shredder is the input of the extrution, on this way you’ll get a more solid material, that will no be lost on the air, as little light particles, and maximize itś recycling efficient… Is just a thought by the way, hope you find the best way 🙂


What about using a cross cutting paper shredder? That should cut well and produce pieces about 4x40mm. I wonder if that would extruder well.


I think 1 step is to extrude it first since it the plastic bag is thin so it can melt and form a solid output where can be shredded. But maybe you need to adjust the extruder speed to have desire output.

By the way, how to create the plastic bag? I was thinking to recycle plastic bag into disposable dustbin bag.

I have cut HDPE plastic bags into large squares and melted them in an aluminum cake pan that was lined with baking paper, in an oven. I kneaded the plastic blob with a metal screwdriver, then pressed the plastic in a wooden mould that was lined with baking paper. I used C-clamps for the compression. I found that air bubbles got trapped in the plastic very easily. I then tried cutting more bags with a scissors, into very thin strips. I melted that batch in an aluminum beverage can, and pressed the plastic with a C-clamp. That seemed to work well for eliminating the trapping of air, but was very time consuming. What I would like to try, is to just feed the plastic bags, one or two at a time, directly into the screw of the extruding machine, with the top of the bags up. My theory is that the extruder will force most of the air out of the top of the bag, and any air that might be left, could pop to the surface of the plastic as it comes out of the nozzle. The filament could then be chopped up into pellets as is shown in the demonstration videos. Then the pellets could be used in any of the machines, just like you would use the flakes from the shredder. An added benefit of this method, would be that all of the different colors of ink on the plastic bags would be throughly mixed into the plastic, giving a uniform color.

Hey Kathleen,

If you’re interested in teenagers getting involved in the issue of plastic pollution you should definitely have a look at the Bye Bye Plastic Bags campaign from Bali.


Dear Cyrille,
I am writing a novella (28.000) ebook to ask teens to help clean up the ocean. Any links you would like me to put in the book that may help you let me know. Take care. Best wishes,

Somebody sent me this link about making plastic sheets using baking paper and an iron. It looks like the result would be great but the technique looks a bit tedious if you are trying to recycle a large amount of bags.

Recycle Plastic Bags Into Usable Plastic Sheets

Hey Marcelo,

Thanks for the reply. How do you propose creating little balls of plastic from the plastic bag sheets?

I also saw a website where they ironed different sheets together in order to form thicker sheets. Wouldn’t this be a good option before putting the plastic in the shredder as well?