Each year, the world produces roughly 100 million tons of flexible multilayer plastic packaging — materials that keep food fresh and pharmaceuticals safe from moisture and oxygen. Yet most of these plastics are nearly impossible to recycle due to their complex, chemically incompatible layers.

Researchers in Michigan State University’s School of Packaging and College of Engineering, in collaboration with the Pacific Northwest National Laboratory, have developed a scalable approach to address this challenge. Supported by a $1.7 million grant from the U.S. Department of Energy, the team designed polyester-based multilayer films that perform comparably to commercial packaging while offering potential for both mechanical and chemical recycling.

New multilayer design

One of the plastics industry’s biggest challenges is making previously unrecyclable plastics recyclable. Led by Professor Muhammad Rabnawaz, Ph.D., the research team set out to re-engineer multilayer structures so they could enter both recycling streams without compromising performance.

The result is a new class of polyester multilayer plastics composed of 80 to 100 percent polyester. The films combine PET (polyethylene terephthalate) for strength and clarity, with PBAT or PBS for sealability and EVOH (ethylene-vinyl alcohol) or PGA (polyglycolic acid) for barrier protection.

By keeping the chemistry within the same polymer family, at least 80 percent, the researchers achieved structures that remain compatible during recycling.

Performance comparable to commercial films

The team produced two main designs using standard cast film melt co-extrusion: a PGA-based trilayer (PET/PGA-PBAT/PBAT) and EVOH-based four-layer films (PET/EVOH/PET/PBS or PET/EVOH/PET/PBAT). This indicates the process can be scaled using existing industry equipment.

Rabnawaz, director of the NSF Center for Plastic, Paper and Hybrid Packaging End-of-Life Solutions (C3PS), described the work as a balance between performance and sustainability.

“These are high-performance materials that happen to be recyclable. Our goal was not to compromise function for sustainability,” he said.

Two recycling pathways

The films were designed to be recovered in two ways:

• Mechanical recycling: The materials were shredded and remelted without compatibilizers. The recycled EVOH-based film (rTETS) retained strong material properties, showing an 11 percent higher tensile modulus and 105 percent greater impact strength than recycled PET (rPET). Unlike conventional multilayers, which become brittle after one cycle, the polyester versions remained flexible and strong.
• Chemical recycling: Using a mild methanolysis process catalyzed at 190 degrees Celsius, the films were depolymerized into dimethyl terephthalate (DMT) and EVOH with approximately 99 percent purity. Recovery yields ranged from 63 to 71 percent, significantly higher than the less than 7 percent yield typically achieved with traditional multilayer packaging. The monomers were of sufficient purity for potential food-grade applications, a key requirement for packaging reuse.

Economic and environmental benefits

Researchers conducted preliminary techno-economic analyses and life-cycle assessments to evaluate cost and environmental impact. Early-stage results indicated that the EVOH-based structure (PET/EVOH/PET/PBS) could be produced for about 32 cents per square meter, similar to current nonrecyclable films. The PGA-based version costs approximately 66 cents per square meter and offers biodegradability advantages.