From Donations to Raw Material
A cornerstone element of our project is the use of recycled plastic. Donated and salvaged plastic often needs a little work before being printer ready. Our plastic preparation process happens before printing and includes sorting, cleaning, cutting down, and granulating.
The plastic that we use for the project all comes through the donation drive at the ReStore. Most donated goods arrive in plastic bins, and it’s rare that the owners want them back. Sometimes the bins are in good shape and make their way to the sales floor, but most of the time they’re too worn out to reuse. Most of the bins are broken, faded, or missing handles and lids, but that’s fine by us. Plastic is plastic! We just make sure to pull out anything that’s too dirty since oil, rust, and other grime aren’t great for the printer
Identifying the Right Plastics
From the secondhand store’s discard pile, we pick out plastic waste that can be reused for 3D printing. There are five common types of recyclable plastic, usually identified by a number inside the recycling symbol on each item.
- Polyethylene Terephthalate (PET or PETE): Used for beverage bottles and packaging.
- High-Density Polyethylene (HDPE): Used for milk jugs, detergent bottles, and pipes.
- Polyvinyl Chloride (PVC): Found in pipes, window profiles, and some food packaging.
- Low-Density Polyethylene (LDPE): Used for plastic bags, films, and flexible containers.
- Polypropylene (PP): Commonly used for food containers, bottle caps, and automotive parts.
Most of the waste we’ve collected this year has been polypropylene. The clear tubs are made from it, and we’ve used that material for much of our testing. These bins are available in large quantities and a variety of shades and colors, allowing us to experiment with a wide range of products in different color combinations. We’ve recently found high-density polyethylene to be very suitable for use as a feedstock for the printer, and are currently running some tests on using HDPE more in the lab.
Sorting, Cleaning, and Tracking
After sorting donations by recycling group and color, we weigh and record each piece of plastic to keep track of where it goes in the process. We follow it from the time it’s accepted to when it’s granulated and eventually printed.
We all realized it was a lot more tedious to clean whole bins than a few flat sheets, so now we break the material down into flats. My favorite part is rinsing the sheets to get rid of all the grime and peeling off any stickers or decals. It can be repetitive, but it’s also a nice chance to relax, talk, and work alongside a teammate.
Granulating the Plastic
We cut the larger sheets from former bins into narrower strips, since the granulator’s opening is limited in size. The granulator then grinds these strips into plastic flakes roughly the size of coarse coffee grounds. Strips of plastic are dosed out in containers (Plastic bins – who’d have guessed…) in batches of about 6-7 kilograms, just enough to fill up the hopper in our granulator.
We feed these batches of plastic sheets through our granulator, and in a cool 20 minutes or so, we’re left with a batch of plastic flakes, ready to be logged, and soon turned into something amazing!
