PET Recycling – From Bottle to Filament

Recycling. A word often related to large companies receiving tons and tons of paper or plastic in an effort to reduce our carbon footprint. However if we look at plastic bottles for instance, humans buy a million plastic bottles per minute, and 91% of all plastic is not recycled. This article is going to cover what makes plastic recycling so important, how to recycle PET and the future of recycling in 3D printing.

What is PET Recycling?

Focusing on plastic bottles here, they have one huge advantage – unlimited recycling potential. PET is one of the few polymers that can be recycled into the same form over and over again. Think of it as a closed-loop recycling solution.

PET recycling loop
The “closed-loop” of PET recycling. Image via PETCO

Recycled PET, or rPET, can be used to make many new products. This can range from clothing, automotive parts, packaging as well as bottles for food/non-food products. Depending on the application required, rPET will be blended with the original PET.

What Are The Uses of Recycled PET (rPET)?

As mentioned above, rPET has many great uses, which includes:

  • Food containers
  • Polyester carpet fiber
  • Fabric for T-shirts
  • Athletic shoes
  • Luggage and upholstery
  • Sweaters and fiberfill for sleeping bags and winter coats
  • Industrial strapping
  • Sheet and film
  • Automotive parts
  • New PET containers
Some recycled PET products

Using rPET in place of the normal or virgin PET has substantial environmental impacts as well as reducing overall energy consumption.

Creating Our Own Filament from Plastic Bottles

Now that we’ve covered the background of recycling PET, how exactly does one go about doing the actual recycling? The one method is simply going to your local recycling company and dumping your plastic waste there, or having it picked up at home if that company provides a pick-up functionality. The other method though is a bit more rewarding – doing it yourself.

We wanted to test of normal plastic bottles can be turned into 3D printing filament. The following is a quick summary of our tests to turn around 30 bottles into filament.

  • Water bottles were collected, cleaned (properly) and any external caps or seals were also removed
  • The bottles were then vacuum sealed and heated to reduce their size
  • Once cooled the bottles were cut into smaller chunks with a saw and a pair of scissors
  • After that, the pieces were shredded into tiny pieces using our SHR3D IT
  • The pieces were then dried at a temperature of 160°C for 4 hours
  • The PET was then fed into our Next filament extruder
  • After multiple tests at different nozzle diameters and temperatures, our team ended up with a great result of PET filament
PET Filament Final Result
Final results of the filament

If you’d like to read the complete test and the different results, you can find the document here.

The Future of Plastic Recycling in 3D Printing

The biggest issue that faces 3D printing recycled filament – dirt. With the above experiment, just cleaning those bottles took a great deal of effort. Now imagine doing it with tons of plastic, often coming from dumps that have been contaminated all forms of impurities.

Also, one has to take note that different types of plastic produce different types of filament. High-density polyethylene — shampoo bottles, for example — are relatively easy to convert into filament, but it’s difficult to print with because it shrinks more than other plastics as it cools. On the other hand, PET, prints well but is brittle, making it difficult to spool as filament.

Recently, we saw the US Department of Defense (DoD) is exploring 3D printing feedstock made from plastic containers that have been left on the battlefield, which can hopefully be reproduced in other government sectors. There’s also Ethical Filament, a company focused on promoting the concept of recycling to produce ethical 3D printing filament that is sold to improve the livelihoods of waste pickers and their communities worldwide. Then there’s the Perpetual Plastic Project (PPP), which is an installation which can directly recycle old plastic drinking cups into 3D printing gadgets as well as other plastic products if needed.

While there is more and more aware of using recycled filament for 3D printing, we still have a long way to go. Hopefully, with the rise in 3D printing over the last few years, more emphasis is being placed on plastic recycling.

 

Bio PE – Extruding the Renewable Polymer

Last year saw a huge surge in the varieties of different 3D printing materials. However, with the world’s focus on saving the environment, not many are coming from biological sources. Even though 3D prints can be recycled into other 3D prints, it is not a zero-sum outcome. With the increase in biological materials though, the end result would be just carbon dioxide and water. In this article we focus on one of these biological materials – Bio PE – and if it can be extruded using our Next filament extruder.

Bio PE Summary

By definition, bio-plastics and biopolymers are the type of plastics and polymers which come from renewable biomass sources. These sources include: vegetable oils, sugarcane, starch and wheat grain. Depending on the products; the global bio-plastics market includes bio-PET, starch blends, PLA, bio-PA, bio-PE and others. Bio PE, or biopolyethylene, is simply polyethylene made out of ethanol. After a dehydration process, it becomes ethylene using these biomass sources. The final product is polyethylene, which properties mimic those of conventional polyethylene.

Applications

The main application for biopolymers is packaging, which makes up around 28% of the total volume shown in 2016. This includes shopping bags, food packaging, bottles and many other uses. Other uses include blow-molded hollow parts such as automotive fuel tanks, injection molded parts, tubes and other applications used in the automotive and consumer-goods industries.

Advantages & Disadvantages

sugarcane field

According to Braskem, the world-leading supplier of bio-PE, a production rate of 200 kilo ton/year of bio-PE would require approximately 450 million liters of ethanol. This would utilize 65 million hectares of Brazilian sugar cane land to produce enough sugar to enable Braskem’s production capacity. This represents 0.02% of the Brazilian arable land.  Clearly, the impact to the sugar cane food supply is quite small.

Another great advantage is that the chemical structure, applications, and recycling are identical to fossil-fuel based PE. Also do not forget that Bio PE is 100% recyclable.

All these advantages do come with one main drawback. Currently, the price of bio-PE is about 50% higher than fossil-fuel PE. In upcoming years though it should see a decrease in price when volumes increase.

Extruding Bio PE + TMP + MAPE

Here at 3devo we were able to acquire some Bio Polyethylene (PE) SHD 7255 LSL, including 20% thermomechanical pulp (TMP) and 6% maleated polyethylene (MAPE). Take note this is just a short summary of our testing. More information can be found here.

Preparation and Extrusion

Cleaning the Next filament extruder has been very important. Either a purging compound or HDPE can be used. Drying the materials was also critical. After 7 hours of drying the material doubled in moisture content over 48 hours (stored in a closed container with silica gel), it was finally ready. Three tests were conducted, using various temperatures and settings. It was interesting to see how quickly the material heated up, and fast fan cooling was vital it to handle more stress. Low temperatures also helped improve the results.

The end result of the extrusion tests

Extrusion Summary

After multiple tests, we conclude that Bio PE + TMP + MAPE combination can be successfully extruded with the Next. Some issues include the TMP particles causing the material to get easily torn apart and the ease at which the material heats up. Cleaning also determines the best results for the final filament.

Conclusion

In the end, bio-plastics and biopolymers are definitely something to focus on in the future of 3D printing. Their unique characteristics make it great for sustainable development. Also now that extruding materials like this is possible, it will be great to see what upcoming projects will be rolling out in the years ahead.