Materials

Wood waste used in renewable, recyclable thermoset plastic alternative

Wood waste used in renewable, ...
A sample of the lignin-based material, which can be thermally broken down and recycled
A sample of the lignin-based material, which can be thermally broken down and recycled
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Researcher Mohammad Morsali shows how an adhesive made from the material was able to bond two aluminum plates together
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Researcher Mohammad Morsali shows how an adhesive made from the material was able to bond two aluminum plates together
A sample of the lignin-based material, which can be thermally broken down and recycled
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A sample of the lignin-based material, which can be thermally broken down and recycled

Not only are most thermosetting resins made from non-renewable ingredients, but they're also difficult to recycle. Swedish scientists have set about addressing those problems, by developing a new lignin-based, thermoset-like material that can be reused several times.

Lignin is a type of organic polymer that makes up much of the support tissue in plants, including trees. It's also a byproduct of the pulp and paper industry, and has previously been put forward for use in applications such as cheaper batteries, waste-derived carbon fiber and stronger concrete.

Researchers at Stockholm University have now combined lignin with a non-toxic cross-linking chemical derived from ethylene glycol, to create a material with characteristics much like those of traditional thermosetting resins. There's no need to chemically alter the lignin beforehand – it's simply "cooked" along with the cross-linker.

The resulting black material can be formed into numerous shapes via conventional casting or injection molding techniques.

Researcher Mohammad Morsali shows how an adhesive made from the material was able to bond two aluminum plates together
Researcher Mohammad Morsali shows how an adhesive made from the material was able to bond two aluminum plates together

Additionally, by varying the lignin-to-cross-linker ratio, it's possible to tweak the material's characteristics – it can be soft and tough, hard and brittle, or even take the form of a strong adhesive. In all cases, it can also be thermally broken back down and reused multiple times, retaining a mechanical strength that is described as being comparable to that of existing engineered plastics.

"The material that we developed is perfectly in line with the current move towards sustainable circular materials," says Asst. Prof. Mika Sipponen. "Owing to its design consisting of so-called dynamic covalent bonds, the material can be formed over and over again by relatively mild heating."

The research is described in a paper that was recently published in the journal ACS Applied Materials & Interfaces.

Source: Stockholm University

3 comments
3 comments
paul314
Interesting. You heat it up to set it, and then you heat it up more to reprocess it.
FatFrass
This is nothing new. Lignin has been exploited as a resin for a hundred years. Particleboard, OSB, hardboard are all held together primarlly by lignin.

The problem that they need to solve is how to make this process use less energy/resources/money than current alternatives.

Nature is very good at getting rid of lignin, so this seems like a solution in search of a problem.
TechGazer
As FatFrass said, it might be a solution in search of a problem, but there might be problems that it does solve. I expect there are applications where this material might have good benefit/cost ratio. If an earlier story here about microplastic particles getting into our brains and causing problems is verified, then safer alternatives might have a huge market. We evolved in an environment which probably has abundant microparticles of lignin, cellulose, keratin, and other organic polymers.