Plastics are incredible because they are so versatile. Plastic waste, however, is problematic because it is so persistent. Right now, the life of a typical piece of plastic follows a linear path: plastic is born from fossil-fuel building-blocks, molded into products, and dumped into landfills and oceans as waste. 

A cyclic life would be more sustainable, where plastic is born from plant-based building-blocks, molded into products, broken back down into building-blocks, reborn into plastic, and so on. This “closed-loop” recycling is challenging because the plastic must be durable enough for product use but breakable under the right conditions. 

To obtain durable yet breakable material, researchers made new plastic that imitates the world’s most common plastic, polyethylene, but with a slightly different chemical make-up. Polyethylene is durable because it is made of carbon and hydrogen atoms, which form strong bonds with each other. Long chains of connected atoms in polyethylene also arrange themselves into an organized 3D structure, further increasing strength. 

The new plastic still has long segments with carbon and hydrogen atoms, like polyethylene, but with small amounts of oxygen atoms, which serve as breaking points. To obtain a strong plastic despite these breaking points, the plastic needed to be made of extremely long chains of connected atoms. Researchers overcame this challenge by using a more reactive combination of molecular building-blocks to grow longer chains. 

The new plastic is just as strong as polyethylene and was 3D printed into a protective smartphone cover and a cup that could withstand boiling water. However, a combination of heat and alcohol completely broke the new plastic down into its molecular building-blocks – even in mixtures with other plastics and dyes that are present in real-world waste streams. The building-blocks were then re-used to make the plastic again in a “closed-loop” lifecycle. 

Plastics with “closed-loop” lifecycles could dramatically reduce the resources needed for products that we use every day, like smartphone covers or cups. While more research is needed to understand how to produce and recycle new plastics on large scales, this initial example is a promising step towards a sustainable future.