Mechanical method uses collisions to break down plastic for sustainable recycling

Although plastics help ensure modern standards of living, their accumulation in landfills and the general environment continues to become a global concern.

Polyethylene terephthalate (PET) is one of the most widely used plastics in the world, with tens of millions of tonnes produced each year in the production of bottles, food packaging and clothing fibers. The durability that makes PET so useful also means it is harder to recycle effectively.

Now, researchers have developed a method to break down PET using mechanical forces rather than heat or harsh chemicals. Published in the journal ChemistryTheir findings demonstrate how a “mechanochemical” method (chemical reactions caused by mechanical forces such as collisions) can quickly convert PET back to its basic elements, paving the way for faster, cleaner recycling.

Led by postdoctoral researcher Kinga Gołąbek and Professor Carsten Sievers of Georgia Tech’s School of Chemical and Biomolecular Engineering, the research team hit solid pieces of PET with metal balls with the same force they would experience in a machine called a ball mill.

This can cause PET to react with other solid chemicals such as sodium hydroxide (NaOH), generating enough energy to break the plastic’s chemical bonds at room temperature, without the need for dangerous solvents.

“We show that mechanical impacts can help break down plastics into their original molecules in a controllable and efficient way,” Sievers said. “This could turn plastic recycling into a more sustainable process.”

Mapping the impact

To demonstrate the process, the researchers used controlled single-impact experiments along with advanced computer simulations to map how energy from collisions distributes across the plastic and triggers chemical and structural transformations.

These experiments showed changes in the structure and chemistry of PET in tiny areas subjected to different pressures and heats. By mapping these transformations, the team gained new insights into how mechanical energy can trigger rapid and efficient chemical reactions.

“This understanding could help engineers design industrial-scale recycling systems that are faster, cleaner and more energy efficient,” Gołąbek said.

Break down plastic

Each collision created a tiny crater with the center absorbing the most energy. In this area, the plastic stretches, cracks and even softens slightly, creating ideal conditions for chemical reactions with sodium hydroxide.

High-resolution imaging and spectroscopy revealed that normally ordered polymer chains had become disordered in the center of the crater, while some chains broke into smaller fragments, increasing the surface area exposed to the reactant. Even without sodium hydroxide, mechanical impact alone caused minor chain breakage, demonstrating that mechanical force itself can trigger chemical change.

The study also showed the importance of the quantity of energy delivered by each impact. Low-energy collisions only slightly disrupt PET, but stronger impacts cause cracking and plastic deformation, exposing new surfaces that can react with sodium hydroxide for rapid chemical degradation.

“Understanding this energy threshold allows engineers to optimize mechanochemical recycling, thereby maximizing efficiency while minimizing unnecessary energy consumption,” Sievers explained.

Closing the loop on plastic waste

These results point to a future in which plastics can be fully recycled back into their original building blocks, rather than being under-cycled or thrown away. By harnessing mechanical energy instead of heat or harsh chemicals, recycling could become faster, cleaner and more energy efficient.

“This approach could help close the loop on plastic waste,” Sievers said. “We could imagine recycling systems in which everyday plastics are treated mechanochemically, giving new life to waste repeatedly and reducing environmental impact.”

The team now plans to test real-world waste streams and explore whether similar methods can work for other hard-to-recycle plastics, bringing mechanochemical recycling closer to industrial use.

“With millions of tonnes of PET produced each year, improving recycling efficiency could significantly reduce plastic pollution and help protect ecosystems around the world,” Gołąbek said.