The 3-D printing revolution has changed the way we think about plastics. Everything from children's toys to office supplies to high-value laboratory equipment can be printed. The potential savings¹ of producing goods at the household- and lab-scale is remarkable², especially when producers use old prints and recycle them. Buying plastic filament³ for printing can be expensive, says Joshua Pearce, the lead researcher in the Open Sustainability Technology group at Michigan Technological⁴ University. Pearce and his students have whittled⁵ the cost of printing to ten cents per kilogram -- down from $30 per kilogram.

 

They made this leap by recycling plastic that had already been printed, using a recyclebot and plastic resin⁶ codes developed by the team.

 

In a new paper from the research group, published in Resources, Conservation and Recycling, the authors lay out how they achieved this price reduction and how to recycle 3-D printed objects more broadly.

 

"The centralized paradigm⁷ of both manufacturing and recycling is being challenged by the rise of 3D printing," Pearce says, explaining that labeling and reusing materials is voluntary.

 

Current labeling schemes, however, are not detailed⁸ enough for 3-D printed recycling. Plastic is not just plastic; there are many kinds, and specific polymers behave in specific ways -- which makes a big difference for 3-D printing.

 

"We want to know about polymers the same way a chemist would," Pearce says, admitting that the seven codes in the US recycling system fall short. In comparison, China has 140 codes for different polymers. "Currently, the most common 3-D printed plastics are grouped in the category seven polymers in the US," he adds.

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