This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Around 450 million metric tons of plastics are produced worldwide each year. The major share of this sheer volume is used only once and then winds up in an incinerator or in landfills.
This also applies to so-called polyolefins, which include polyethylene (PE) and polypropylene (PP). As packaging materials and films, they account for approximately half of our plastic consumption. Although polyolefins can be melted down and recast into new shapes, this process results in significant quality losses.
The dyes in the waste impart a dark color to the recycled material, while the heating process damages its quality: as a result, the material is only suitable for low-grade applications such as plant pots or paving slabs. So far, it has proved impossible to selectively break down polyolefins into their basic building blocks—the monomers—from which new, high-quality polymers could be synthesized. Olefins, which consist exclusively of carbon and hydrogen, lack the oxygen, nitrogen or chlorine atoms required for targeted cleavage reactions.
To date, the only feasible method is random breakdown by way of an energy-intensive heating process known as pyrolysis. This produces petroleum-based feedstocks from which the monomers must be rebuilt. Now, a team of researchers led by polymer chemist and ETH Professor Tae-Lim Choi has developed a process that allows polyolefins to be upcycled into higher-value plastics, rather than simply being recycled in a manner that reduces their value.
To achieve this, they graft additional polymer chains with new functionalities onto the plastics. The research is published in the Journal of the American Chemical Society. ETH Zurich has patented the process and nominated it for the Spark Award.
Hongsik Kim, the senior scientist in Choi's group who was primarily responsible for developing the method, produced adhesives as the first product using standard plastic bags and bottles. Their adhesive strength with various materials such as metal, glass or wood meets the requirements for an industrial adhesive employed in load-bearing and high-stress joints in vehicle or equipment manufacturing. The range of potential applications, however, is much broader: the additional polymer chains allow the entire spectrum of chemical functionalities to be introduced into polyolefins: from polar groups that interact with water to varying degrees, through acids and bases, to chemical groups capable of undergoing very specific reactions.
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