Plastic Recycling - Shredding

[Ayydan]

I've been casting in silicone a stiffer mold for melting down scraps, I'm hoping to use some plaster of Paris to act as a better weight, with some embedded rods to act as integrated spacers. Hopefully allowing it to press to a more even thickness. One concerning thing to note is that the center of my earlier melts was very thin, and the result was brittle. I'm hoping this was simply caused by the silicone being too thin to resist buckling. This will likely be the most annoying aspect to nail down...

[Ayydan]

Just finished the silicone mold, next step will be to setup the plaster press component 

   

Yooo that's awesome! Looks very well done

---

I've been casting in silicone a stiffer mold for melting down scraps, I'm hoping to use some plaster of Paris to act as a better weight, with some embedded rods to act as integrated spacers. Hopefully allowing it to press to a more even thickness. One concerning thing to note is that the center of my earlier melts was very thin, and the result was brittle. I'm hoping this was simply caused by the silicone being too thin to resist buckling. This will likely be the most annoying aspect to nail down...

Do you think it's thin because of buckling, or because of shrinkage when cooling? The center would stretch as it shrinks, which would also explain the brittleness from the added stress.

Good job, you just figured out how to file harden PLA

[Ayydan]

Might be shrinkage, but I'd rather pretend it isn't for now, since that'd be more difficult to resolve.

I may have to implement a slower cool down

[Ayydan]

Well... After weeks of experimenting with silicone molds and the like, I've found the best means so far for getting a consistent, grindable output. I essentially just used my original idea with two silicone sheets being pressed together and added some walkway pavers. I wish I'd discovered this before wasting money on silicone, but lessons have been learned.

I'll likely still try to use my silicone mold to melt down irregularly shaped objects before pressing them flat. I'll update with a process diagram after some more experimentation.

[Ayydan]

Haven't updated in a while. I've gotten a bit of a process for shredding sorted out for now, and have begun extruding some material for testing!

The current shredding process is:

1. Line a silicone baking mat with ~100g of material (I only process PLA right now)
2. Bake in a toaster oven on convection at 200C for 30 minutes. This creates a plastic "biscuit"
3. After allowing the biscuit to cool, they are collected in a bucket until processed further
4. A biscuit is placed between two nonstick grill mats, then pressed using a t shirt heat press at 230C for ~5 minutes
5. The grill mats are removed, and sandwiched between two sheets of MDF to cool (I want to try seeing if other materials will allow the sheets to cool faster)
6. The sheets are then passed through my modified office shredder and collected in a standard home supply store bucket

Once a reasonable amount of material has been collected, the current process for extrusion is:

1. Mix virgin PLA to regrind material at a ratio of 1:1 by mass (I will try to use less virgin material later, but for now I want to make sure the process is sound)
2. Wash the material to remove any residue or foreign elements (this step may be optional, but I want to be careful)
3. Dry to material in a food dehydrator for 12 hours
4. Feed into the filament extruder and process

Currently I find the best results with my artme3d extruder using the following settings:

Temperature: 180C
Extruder RPM: 20.20
Fan speed: 28

All other settings are more or less stock. Measuring the produced result every now and then currently has it being produced at around 1.77-1.73mm, but further testing is needed to observe consistency. In addition, these parameters will likely vary with a lower percentage of virgin material in the batch.

I am hoping to test this first consistent product once it has completed extruding and will follow up with material results.

  PXL_20240725_183048683.TS.mp4

[Ayydan]

1:1 blend extruded quite nicely, will have print images shortly

1:9 virgin to regrind doesn't extrude as well as I'd like, it's a lot thinner and cools very quickly.

I'll probably try to go for 1:3 virgin to regrind next to see if that performs better without requiring quite as much virgin material.

[Ayydan]

Here is the resulting benchy from the 1:1 trial, no flow compensation 

   
   
   

[Ayydan]

A few lessons have been learned so far in the use of this machine.

1. Make sure that the unit has stabilized at the target temperature for a few minutes, otherwise the melt filter will get damaged
2. Don't run pure regrind (at least not if yours is a similar quality to mine), the melt is not even close to consistent enough otherwise

I ran a 100g batch of 70:30 blend PLA that seems to have come out fairly nicely, which I am printing a benchy from now. If all looks good I'll move onto a larger batch size to validate my process. Unfortunately between a bad ratio and insufficient heating, I had damaged the melt filter twice so far, requiring replacement. From this experience, I think it would be best to avoid changing the target temperature any time the machine is actually running, as it likely allowed the melt to cool too much.

Once I have managed a larger batch size I will follow up with some procedure images hopefully.

[Ayydan]

Sadly despite my best efforts I've had the machine jam up for the third time despite my best efforts to keep the melt filter from introducing flow restriction. I may try a run without any form of melt filter to see if I can get more consistent results. If the results from this don't hold up I may have to take another approach to my shredding solution, as it is likely that my resulting granulate is not sufficiently uniform to get consistent extrusion. This would likely be a very expensive solution, so I will hopefully not need to take this course.