How to Recycle PET Plastic into 3D Printing Filament

PET  is the most recycled plastic, having a recycling rate of 58.2% After it is recycled, it is called rPET, or recycled PET.  Many companies thefefore are now aiming to reuse it and recycle it as new packaging. For example, some shoemakers have been turning rPET into sneakers.

Sneakers and packaging aren’t the only products you can recycle PET into; by turning it into 3D printing filament and 3D printing, you can produce unique designs and new products! 

We’ve been able to extrude rPET into filament and print with it successfully and have collected all the steps into the step-by-step guide below so that you can too! 

Step 1: Prepare the PET Bottles

The first step to recycling your bottles is to prepare them by cleaning and shredding them to the appropriate size. To get them ready for shredding we have to clean them from any residue, contamination and extra materials. The steps for this are:

1. Unscrew the caps from the bottles and cut off the security rings using a cutter or knife. Be careful as the hard plastic might be challenging to cut with cutters.
2. Remove the labels from the bottles using scissors or cutters. There might be residue glue leftover. We suggest removing it using a piece of cloth or cotton swab and Acetone. Acetone dissolves the glue, and thus it becomes easy to remove it.
3. Clean the internal of the bottle using dishwasher soap (or any soap available at hand, we are generous here) and brush.
4. Ensure that you have removed all the solid residue (in milk bottles), liquid, or any dust contamination. Contamination can cause inconsistencies and flaws in the recycled product.
5. Dry the bottles by placing them upside down. You can put them in the sun for a speedy drying process but make sure the place is free from dust.
6. Once dried, reduce the bottles in size. We advise you to do so using one of the following methods:
   • Crushing the bottles flat by hand,
   • Using a vacuum cleaner to shrink the bottles by removing the air,
   • Using scissors to cut the bottles into small pieces (be careful as the sharp edges of the bottles can hurt you).

Step 2: Shred the Bottles

Now that the bottles are clean and cut into smaller pieces, they are ready to be placed into a plastic shredder. Our aim is to get them into smaller chunks no bigger than 4mm. When you’ve put them through your shredder, check the size of your pieces using Vernier Calipers or a ruler.

If after the first feeding the sizes are bigger than 4mm, feed the regrinds through the shredder once again.

The top filament was extruded without drying the regrind and the bottom after drying the regrind.

Step 4: Preheat the Filament Maker

Typically, new filament makers come preloaded with pellets of materials like PLA. If the filament maker is already in use, it can have previously used material in the machine. In either case, to obtain the pure extrusion of PET, it is necessary to remove that material. These materials can have the same or different melting points than PET. For example, our filament makers have PLA pellets by default.

PLA has a working temperature of 60-190^oC, whereas PET’s temperature range is between 350 to 490^oC. So, if PLA gets heated to the working temperature of PET, the PLA will degrade or decompose, both of which we do not want. That’s why a transition material which is workable between the temperature ranges of PLA and PET is used. In our case, we used Devoclean EZ MidTemp, which works for both the cleaning and transitioning process.

How Transitional Material Works.

To preheat and remove the existing material from the machine, follow these guidelines;

1. If the current material in the filament maker is PLA, the recommended settings are:
   • Heater Temperature to 200^oC,
   • Extruder speed to 15RPM,
   • Filament fans to 30%.
2. Start the machine and wait until the hopper gets emptied from all the existing material. To speed up the process, you can use a vacuum cleaner to remove the current PLA pellets from the hopper. (Usually, there is protection gauze on top. Unscrew the screws and slide to remove the gauze).
3. Pour the Devoclean EZ MidTemp or HDPE Flush into the hopper. The recommended amount is 250g.
4. Wait until all the Devoclean from the hopper has been extruded, the output of Devoclean is white, bubbly, and foamy.
5. Once you observe the hopper becoming empty, change the machine settings for PET. We recommend:
   • Heater Temperature to 270^oC,
   • Extruder speed to 7RPM,
   • Filament fans to 30%.
6. Continuously check for the hopper to prevent it from becoming empty. The machines have a built-in feature to turn them off if the hopper is empty for more than 10 minutes. However, you can turn this feature off in the settings.
7. Observe the temperature of all the heaters; there are four of them. To reach 270^oC, let all the pellets in the hopper get emptied.
8. Now, feed in the PET regrind in the hopper. Use a small amount of PET at a time, as overloading can cause blockage and slow down the process.
9. If you have already opened the safety grid, you can plug in the feeder and place it in the hopper. The feeder generates vibratory motions that help move the regrind through the extruder easily, as its sharp edges can make this difficult.
10. During the extrusion, keep an eye on the contents of the hopper. Make sure that it stays filled to avoid any obstruction in the extrusion. Once the output is no longer foamy or bubbly, you’ll know that all the Devoclean has been extruded, and we are now extruding rPET. 

The next step is to tune the settings to get the perfect extruded filament.

Spool the Filament

After you begin to observe a continuous filament of desired quality, it is time to wind the filament on the spool. 

1. Take the empty spool and tighten the spool holder on this empty spool.
2. Go to the settings, start the spooling wizard, and follow the instructions as indicated on the screen.
3. Cut the filament off the product and attach it to the spool by guiding it through the positioner.
4. Place the spool on the winder shaft, tighten the winder and start the winding.
5. Close the safety door. 
6. During the process of spooling, keep an eye on the regrind quantity in the hopper. Fill the hopper with more regrind as needed.
7. When the spool is wounded, cut the filament using scissors and remove the full spool by untightening the screw.
8. As stated earlier, PET absorbs water. So, either uses the filament directly after spooling or store the spool in an airtight environment.

Purge the Filament Maker

Since there is molten material inside the Filament Maker, it is necessary to remove it before turning it off to prevent hardening in the Filament Maker and clogging the machine. You can do this by:

1. Allowing the materials in the hopper to completely use or vacuuming the regrind out of the hopper.
2. Add Devoclean EZ MidTemp in the hopper. We recommend using 50 grams of these pellets.
3. Turn up the RPM to 15 to speed up the process.
4. Remember, the output of Devoclean EZ MidTemp should be foamy and bubbly.
5. Once all the Devoclean pellets are used, stop the extrusion, and turn off the machine.

Extrusion Trouble Shooting

During the extrusion, you may encounter several faults and product flaws. Below you’ll find the most common issues you may encounter and how to troubleshoot them.

2. Solid Bumps Appearing in the Filament

Solid bumps in the filament indicate the presence of contamination or impurities in the regrind.

Troubleshoot: Make sure to clean your PET bottles properly and protect your regrind from dust (storing it in a container until use can help).

3. There is Build-up in the Nozzle

Nozzle build-up is due to the premature hardening of the product coming out of the nozzle. The possible reason for these faults can be the cold nozzle.

Troubleshoot: We recommend increasing the temperature settings of Heater H1, decreasing the filament cooling fan speed, lowering the fan orientation from the nozzle, or having proper insulation of the nozzle area through a magnetic plate.

4. The Molten Filament is Collapsing

Nozzle build-up is due to the premature hardening of the product coming out of the nozzle. The possible reason for these faults can be the cold nozzle.

Troubleshoot: The troubleshooting involves lowering the heating by decreasing the temperature of the heaters. In addition, we recommend reducing the fan cooling. During the troubleshooting, make sure that you do not reduce the temperatures too much, or nozzle build-up may occur.

Tips for 3D Printing Your Dream Design

Now that you have your spool full of PET filament, you can use it to 3D print your dream design. These are the steps we took to make it happen:

1. Open the slicer software on your computer. We used Cura, but you can use any of the ones you are comfortable with and upload the STL file.
2. In the printing settings, set the settings to the following temperatures:
   • Printing temperature to 255^oC,
   • Bed temperature to 70^oC.
3. For better adhesion between the subsequent layer, we suggest you turn print cooling off.
4. You can decrease the print speed to compensate for the lack of cooling. We recommend the settings to be 20mm/s.
5. Start the printing and enjoy the process!