Upcycling of Polyethylene Widely used as a raw material for nylon

Upcycling involves transforming waste products into new, often higher-quality products. The concept is particularly popular among hobbyists. However, the idea can also be applied on an industrial scale—for example, by producing polyamide from polyethylene waste. Researchers in Rostock are working on exactly that. 

It would greatly reduce the burden on the environment and climate if, in the future, nylon could be produced largely from plastic waste instead of from petroleum, as has been the norm until now. Chemists at the Leibniz Institute for Catalysis (LIKAT) are pursuing this approach. They have succeeded in selectively converting polyethylene—the main component of all plastic waste—into dicarboxylic acids, which can serve as chemical precursors for nylon.

The reaction proceeds under mild conditions and does not even require a catalyst. The goal is to develop a process on a pilot-plant scale. To that end, the team aims to increase selectivity and elucidate the reaction mechanisms.

Pyrolysis Is No Longer Feasible

Polyethylene (PE), together with polypropylene (PP), account for four-fifths of plastic waste—an estimated 400 million metric tons per year worldwide. Pyrolysis has become the established method for chemically recycling these polyolefins, as Dr. Esteban Mejía, program director at LIKAT, explains: “The plastic is burned in a controlled manner at temperatures of up to 600 degrees Celsius.”

While the result is indeed “high-quality oil” and the process does not emit any CO₂, pyrolysis’s enormous energy consumption leaves such a large carbon footprint that environmental authorities are sounding the alarm. In the U.S., pyrolysis plants are already being shut down.

Pyrolysis is a process used in the field of chemical recycling. In this process, plastic waste is not simply shredded and remelted, as in mechanical recycling, but rather broken down into its basic building blocks (monomers).

In pyrolysis, plastic is thermally decomposed at high temperatures in the absence of oxygen. This process produces oils, gases, and solid residues (coke/ash), which can be reused as raw materials. Pyrolysis is currently the predominant technology, particularly in Germany.

Reactive Oxygen Species as a Tool

This raises the question of alternatives. Researchers are aware of a number of catalytic processes that work through oxidation, similar to pyrolysis, says Esteban Mejía. “In these processes, a reactive oxygen species—which we call ROS—forms on the polyethylene surface.” As chemists now know, these are precisely what matter. ROS chemically break down the polyethylene. “They essentially eat away at the material,” Mejía sums it up.

However, this reaction requires high pressure, which makes the process explosive. “It cannot easily be scaled up to a level relevant for practical applications.” Furthermore, the catalysts are based on precious metals, which makes the whole process expensive and also dependent on the volatile raw materials market.

During their literature review, the group found reports from colleagues who had produced polyethylene dicarboxylic acid with non-specific chain lengths, using methods that included highly concentrated nitric acid at 180 degrees Celsius and in a microwave. “Those are pretty harsh processes,” says Mejía, “but we were intrigued by the idea of pursuing the nitric acid approach further and simplifying the process.”

"Simpler" means: diluted and mixed with H₂O₂

Since April 2026, a postdoctoral researcher, Dr. Satyajit Panda, has been working on the topic, occasionally assisted by a master’s student from the University of Rostock. Through further research and trial and error, the group ultimately arrived at a simple reaction. The effect was fascinating: “You put pieces of a plastic bag into a test tube containing highly diluted nitric acid and hydrogen peroxide, heat the mixture to a maximum of 120 degrees, and watch as the polyethylene dissolves,” said Mejía.

Controlling the reaction, however, is not quite so simple. “A specific heat input regime is important,” explains Mejía. This is because the conversion of PE to dicarboxylic acid involves several stages. If the intermediate products are allowed too much time, the reaction proceeds suboptimally and ultimately results in a complex mixture.

Selectivity and Reaction Mechanism

Dicarboxylic acid consists of chains of carbon atoms of varying lengths. Previous publications have reported reaction results involving chain lengths ranging from two to over 40 carbon atoms. “The authors used it as a surfactant in soap production,” says Mejía. 

The target product of the Rostock chemists, on the other hand, is a viable starting material for polyamide (PA), better known as nylon. Dicarboxylic acid with a chain length of exactly six carbon atoms is suitable for this purpose. And that places higher demands on the selectivity of the reaction and on any separation processes.

In their experiment, the LIKAT chemists have already been able to narrow down the chain length of their product to between four and ten carbon atoms. They hope to further improve this in collaboration with Prof. Dr. Udo Kragl from the Department of Chemical Engineering at the University of Rostock. Among other things, they have applied for project funding from the DFG for this purpose.

In this project, they also plan to work with analysts at LIKAT to elucidate the reaction mechanism: The primary goal is to determine which intermediates are formed during the reaction process, when they are formed, and how quickly. There is also a collaboration with a colleague from the University of Guayaquil (Ecuador) who is investigating, through photochemical experiments, the influence of light on the function of ROS, the reactive oxygen species.