Researchers Develop Self-Repairing Corrosion Protection

Fluorescent corrosion protection on a metal plate. Photo courtesy of March D’Elia/ ETH Zürich.

Researchers at ETH Zürich (Zürich, Switzerland) recently presented a new solution to combat corrosion. In an effort led by Markus Niederberger and Walter Caseri from the Laboratory for Multifunctional Materials, they have developed a plastic known as poly(phenylene methylene), or PPM for short, that could greatly improve and simplify corrosion protection. The ETH researchers also worked with partner universities in Austria, Italy, Spain, and the UK. 

When mixed as a paint and heated, PPM can be sprayed onto a surface and become solid. The polymer indicates holes and cracks in the protective layer by failing to fluoresce. What’s more, it repairs any damage to itself without further external intervention, and can be completely removed and recycled with only minimal material loss. The recycled polymer than then be applied to another surface with no loss in its special properties and functions. 

About ten years ago, researchers in Niederberger’s lab were working on the production of nanoparticles in a special organic solvent. Under certain conditions, the solvent became solid and polymerized. “That was unintentional and unwanted,” Niederberger recalls. “We didn’t know what to do with it at first either.” 

But they then discovered that the polymer they had created by accident had another interesting property in addition to its high thermal stability: it fluoresced even though conventional knowledge suggested it shouldn’t. This led the researchers to specifically refine the material. After a doctoral student initially improved the polymer’s synthesis, another doctoral student named Marco D’Elia was tasked with finding a useful application for PPM. 

“And he did this job with flying colors,” says Caseri, who supervised D’Elia, adding that D’Elia’s contacts with corrosion experts at the Universitá degli Studi di Milano also proved fruitful. 

Laboratory tests revealed that a PPM-based coating protects metals, especially aluminum, against corrosion. Even though the protective coating can be applied in layers that are up to ten times thinner than conventional protective agents, such as those based on epoxy resins, it is durable and seals any damage to itself. 

“Self-repair mechanisms are in great demand, but they’re very difficult to attain, and good solutions are still rare,” Caseri says. To achieve self-repair usually requires chemical additives, which migrate in the polymer over time and are released into the environment. Not so with PPM: “This material doesn’t require any additives,” says Caseri. 

PPM is also more sustainable than previous corrosion protection materials because it can be completely removed and recycled at the end of the product’s life. While some polymer material is lost in the process, the recycling rate is very high at 95%. In their tests, the researchers were able to reuse the material five times. 

Studies on the sustainability of PPM-based corrosion protection also shows that the polymer performs better than epoxy-based corrosion protection materials when it comes to both environmental impact and human health. “There are really only two disposal solutions for epoxy resins; incineration or landfill,” D’Elia says. “Our product allows for a third solution: recycling.” 

Nevertheless, PPM is not completely harmless to the environment. “Synthetic products always have an impact,” says D’Elia. “But if you choose the right approach, you can limit that impact to a great extent.” 

D’Elia hopes to see PPM commercialized, and to that end the researchers have applied for a patent for their invention that is currently pending. They are also currently looking for an industry partner to further develop the product, as well as manufacture and develop it on a larger scale. “Our technology is pretty advanced, but before we can sell it as a product, there are still some improvements for us to make,” D’Elia says. 

For his part, Caseri is proud of what he and his fellow researchers have achieved. The chemical synthesis, the characterization of PPM’s molecular structure, and the study of material properties that were not expected for this type of polymer, such as fluorescence, show “all the versatility of materials science,” says Caseri. 

Source: ETH Zürich,