ETH process turns polyolefin waste into load-bearing adhesives

By Elena Vasquez

Around 450 million tons of plastic are produced worldwide each year, and a team at ETH Zurich has developed a patented, one-step process that converts polyethylene (PE) and polypropylene (PP) waste into a high-strength adhesive instead of downgrading it into low-grade products.

What waste stream is ETH Zurich targeting?

PE and PP are polyolefins. Used in packaging materials and films, they account for approximately half of global plastic consumption. Most of the 450-million-ton annual output gets one use before ending in an incinerator or landfill, and the research targets that disposal challenge directly.

Conventional melt-and-recasting causes significant quality loss: dyes darken the recycled material and heating damages it, limiting output to products such as plant pots and paving slabs.

Selective breakdown into basic building-block monomers has not proved feasible for polyolefins. Olefins consist only of carbon and hydrogen and lack the oxygen, nitrogen or chlorine atoms required for targeted cleavage reactions.

The established alternative is random breakdown through energy-intensive heating known as pyrolysis. That process produces petroleum-based feedstocks from which the monomers must be rebuilt.

How does the one-step process work?

Under the method developed by polymer chemist and ETH professor Tae-Lim Choi, additional polymer chains with new functions are grafted onto polyolefins. The entire process runs in one step: researchers dissolve plastic waste in a chlorinated solvent, then add the monomers needed to synthesize the desired graft polymer.

The method avoids expensive special reagents and catalysts and does not require high process temperatures. It also allows direct control over the reaction.

Hongsik Kim, the senior scientist in Choi’s group and primarily responsible for developing the method, explained: “We are able to control how many radicals are generated – and consequently how many sites in the polyolefin chains are activated for grafting – by adjusting the degree of chlorination of the solvent and the wavelength of the light as required.”

Chlorinated solvents are a key chemical component. Short-wavelength light irradiates the solvent, producing highly reactive individual chlorine atoms known as radicals. Those chlorine radicals transfer their reactivity to carbon atoms in the polyolefin chains, creating carbon radicals that serve as starting points for synthesizing additional chains.

The underlying idea came from a collaboration between Choi and the group led by Athina Anastasaki, ETH Zurich professor of sustainable polymers. Anastasaki has applied the same chlorine-radical principle to recycling acrylic glass, also known by the brand name Plexiglas.

What has the team demonstrated?

Kim produced adhesives as the method’s first product, using standard plastic bags and bottles as feedstock. The material’s strength with metal, glass and wood met the requirements for an industrial adhesive used in load-bearing and high-stress joints in vehicle or equipment manufacturing.

Choi described that result as a starting point rather than the end product: “The adhesive is a first-generation product. In the future, plastics with entirely new properties will be possible. In principle, additional polymers with every conceivable chemical functionality can be grafted onto polyolefins.”

The grafted chains can introduce polar groups that interact with water to varying degrees, acids and bases, and chemical groups capable of highly specific reactions. Kim said the adhesive could also act as a binding agent, bonding low-grade recycled plastic into a more durable, higher-quality material.

What will decide commercial uptake?

ETH Zurich has patented the process and nominated it for the Spark Award, a prize honoring the most promising patent application of the year. The patent was published six months ago, and the researchers have already established numerous industry contacts.

One collaboration concerns food packaging made from polyolefin plastics. The package is intended to be waterproof and prevent oxygen from penetrating, so food oxidizes less in the freezer and develops less tarnish than with current PE and PP packaging.

The announcement identifies no partner, commercial plant capacity, production start date or regulatory filing. An adhesive product has been demonstrated, but no operating commercial line is reported.

The next market milestone is whether an industrial partner takes the patented method from the demonstrated adhesive and food-packaging collaboration into commercial production; no partner, scale or timetable has been disclosed.