New Method Uses Collisions to Break Down Plastic for Sustainable Recycling

While plastics help enable modern standards of living, their accumulation in landfills and the overall environment continues to grow as a global concern.

Polyethylene terephthalate (PET) is one of the world's most widely used plastics, with tens of millions of tons produced annually in the production of bottles, food packaging, and clothing fibers. The durability that makes PET so useful also means that it is more difficult to recycle efficiently.

Now, researchers have developed a method to break down PET using mechanical forces instead of heat or harsh chemicals. Published in the journal Chem, their findings demonstrate how a "mechanochemical" method - chemical reactions driven by mechanical forces such as collisions - can rapidly convert PET back into its basic building blocks, opening a path toward 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 make the PET 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 hazardous solvents.

"We're showing that mechanical impacts can help decompose plastics into their original molecules in a controllable and efficient way," Sievers said. "This could transform the recycling of plastics into a more sustainable process."

Mapping the Impact

In demonstrating 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 structure and chemistry of PET in tiny zones that experience different pressures and heat. By mapping these transformations, the team gained new insights into how mechanical energy can trigger rapid, efficient chemical reactions.

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

Breaking Down Plastic

Each collision created a tiny crater, with the center absorbing the most energy. In this zone, the plastic stretched, cracked, and even softened slightly, creating ideal conditions for chemical reactions with sodium hydroxide.

High-resolution imaging and spectroscopy revealed that the normally ordered polymer chains became disordered in the crater center, 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 breaking, showing that mechanical force itself can trigger chemical change.

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

"Understanding this energy threshold allows engineers to optimize mechanochemical recycling, maximizing efficiency while minimizing unnecessary energy use," Sievers explained.

Closing the Loop on Plastic Waste

These findings point toward a future where plastics can be fully recycled back into their original building blocks, rather than being downcycled or discarded. 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 where everyday plastics are processed mechanochemically, giving waste new life repeatedly and reducing environmental impact."

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

"With millions of tons of PET produced every year, improving recycling efficiency could significantly reduce plastic pollution and help protect ecosystems worldwide," Gołąbek said.

CITATION: Kinga Gołąbek, Yuchen Chang, Lauren R. Mellinger, Mariana V. Rodrigues, Cauê de Souza Coutinho Nogueira, Fabio B. Passos, Yutao Xing, Aline Ribeiro Passos, Mohammed H. Saffarini, Austin B. Isner, David S. Sholl, Carsten Sievers, "Spatially-resolved reaction environments in mechanochemical upcycling of polymers," Chem, 2025.