Feed Your 3D-Printer With Used Milk Jugs

Made in China style plastic products can be produced at home with low-cost 3D-printers working with free open-source designs--but the source material, plastic filament, still has to be bought for good dollars. This could change with a new method for do-it-yourself recycling of polyethylene into 3D-printing ready plastic filament.

Joshua Pearce, an associate professor of materials science and engineering at Michigan Technological University already made a prototype device for this purpose, called RecycleBot. He already uses open-source 3D printing to save thousands of dollars by making everything from his lab equipment to his safety razor, but thought that he could save even more by getting the source material for free.

"One impediment to even more widespread use has been the cost of filament," says Pearce. Though much less expensive than buying most manufactured products, using 3D-printers to make useful objects still incurs significant costs for the plastic filament.

Using open-source 3D model files downloaded from sites like Thingiverse, which now holds over 54,000 open-source designs, 3D printers usually work similar to ink-jets to make all kind of objects by laying down countless thin layers of plastic in a specific pattern on top of each other. While high-end printers can cost tens of thousands of dollars, simple DIY units can already be had for between $250 and $500--and can increasingly be used to make parts for other 3D printers, driving the cost down ever further.

Pearce chose milk jugs as the first object to recycle, and they do have the advantage to be an uniform and abundantly available piece of trash, that is otherwise a costly nuisance, either to recycle or to bury in a landfill. Pearce and his research group cut the labels off milk jugs, washed the plastic, and shredded it. Then they ran it through a homemade device that melts and extrudes it into a long, spaghetti-like string of plastic. Their process is open-source and free for everyone to make and use at Thingiverse.com.

The process isn't perfect. Milk jugs are made of high-density polyethylene, or HDPE, which is not ideal for 3D printing. "HDPE is a little more challenging to print with," Pearce says. But the disadvantages are not overwhelming. His group made its own climate-controlled chamber using a dorm-room refrigerator and an off-the-shelf teddy-bear humidifier and had good results.  With more experimentation, the results would be even better, he says. "3D printing is where computers were in the 1970s."

The group determined that making their own filament in an insulated RecycleBot used about 1/10th the energy needed to acquire commercial 3D filament. They also calculated that they used less energy than it would take to recycle milk jugs conventionally.

RecycleBots and 3D printers have all kinds of applications, but they would be especially useful in areas where shopping malls are few and far between, Pearce believes. "Three billion people live in rural areas that have lots of plastic junk," he says. "They could use it to make useful consumer goods for themselves. Or imagine people living by a landfill in Brazil, recycling plastic and making useful products or even just 'fair trade filament' to sell. Twenty milk jugs gets you about 1 kilogram of plastic filament, which currently costs $30 to $50 online."

Pearce's research is described in depth in two articles: "Distributed Recycling of Waste Polymer into RepRap Feedstock,"coauthored with Christian Baechler and Matthew DeVuono of Queen's University and published in the March issue of Rapid Prototyping ; and "Distributed Recycling of Post-Consumer Plastic Waste in Rural Areas," coauthored by Michigan Tech's Jerry Anzalone (CEE) and students Megan Kreiger (MSE), Meredith Mulder (MSE) and Alexandra Glover (MSE), which will appear in the Proceedings of the Materials Research Society.