In a move that solves two problems by creating one very sturdy new one, MIT engineers have a plan for the world's plastic waste: turn it into your floor joists. A team led by professor David Hardt, SM '74, PhD '79, and lecturer AJ Perez '13, MEng '14, PhD '23, has laid out a vision for using recycled plastic to 3D-print construction-grade beams and trusses, offering a potential alternative to wood framing that doesn't involve clear-cutting three Amazon rainforests.
While some companies are using large-scale 3D printing for walls with concrete or clay - materials famously great for the environment - these engineers are among the first to explore printing structural framing elements from recycled plastic. Their design mimics traditional wooden trusses, resembling a ladder with diagonal rungs. For their test, they obtained pellets of recycled PET polymers and glass fibers from an aerospace materials company and used them as "ink" in a room-size printer.
The result? They printed four long trusses, configured them into a conventional plywood-topped floor frame, and watched it hold over 4,000 pounds, far exceeding key US Department of Housing and Urban Development building standards. Each plastic truss weighs about 13 pounds, light enough to avoid needing a flatbed truck, and an industrial printer can crank one out in under 13 minutes. Crucially, they're developing the process to work with "dirty" plastic that hasn't been cleaned.
"We've estimated that the world needs about 1 billion new homes by 2050. If we try to make that many homes using wood, we would need to clear-cut the equivalent of the Amazon rainforest three times over," says Perez, neatly summarizing the housing crisis with a side of ecological horror. The key, he says, is recycling dirty plastic into building products that are lighter, more durable, and sustainable.
The grand vision involves sending trash like used bottles and food containers directly into a shredder, turning them into pellets, and feeding them into a large-scale 3D printer to become structural components. Perez imagines shipping-container micro-factories placed near plastic sources, like football stadiums, using off-the-shelf shredding tech. The printed parts would be so light you could transport a whole building's frame on a moped or pickup truck to where it's needed, presumably while feeling very smug about your carbon footprint.