Buying plastic filament for 3D printing can be expensive, says Joshua Pearce, the lead researcher in the Open Sustainability Technology group at Michigan Technological University. Pearce and his students have cut the cost of printing to $0.10 per kilogram (kg), down from $30 per kg.

In a paper published in Resources, Conservation and Recycling, the authors lay out how they achieved this price reduction by recycling plastic that had already been printed. They also explain how to recycle 3D-printed objects more broadly.

Current labeling schemes are not detailed enough for 3D printed recycling, the researchers say. Plastic is not just plastic, they say; there are many kinds, and specific polymers behave in specific ways, which makes a big difference for 3D printing.

"We want to know about polymers the same way a chemist would," Pearce says, arguing that the seven labeling schemes in the U.S. recycling system fall short of what may be needed. By comparison, China has 140 codes for different polymers. "Currently, the most common 3D-printed plastics are grouped in the category seven polymers in the U.S.," he says.

The two most common plastics for 3D printing are PLA (polylactic acid) and ABS (acrylonitrile butadiene styrene). Although they are distinctly different, being lumped with so many others in one category makes it difficult to reuse these plastics.

Pearce and his team developed a new resin code identification system based on the Chinese codes and made the system expandable to accommodate innovations.

"We also demonstrated how to weave recycling symbols into 3D-printed objects using open-source and parametric scripts for our new print codes," Pearce says. The scripts are available on the website Appropedia.