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Thursday, June 24, 2021

New biodegradable single-use plastic which ‘eats itself’ revealed

Scientists invent self-eating biodegradable single-use plastic.

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Scientists have developed a new biodegradable single-use plastic that ‘eats itself’.

The material is manufactured to contain enzymes which then break down as it is exposed to water and heat.

The technology could soon be used in items like plastic forks and bags which litter the planet’s oceans.

The developers think it could also be used in glue so some common electronics could be easily disassembled and their parts re-used.

They hope it could mean a final end to the environmental blight of single-use plastics.

Currently, “compostable” plastic bags, utensils, and cup lids don’t break down during typical composting and contaminate other recyclable plastics, creating headaches for recyclers.

So most of these materials – made mainly of the polyester known as polylactic acid, or PLA – just end up in landfills and last as long as forever plastics.

New biodegradable single-use plastic which ‘eats itself’ revealed

One of the researchers behind the new plastic, Dr. Ting Xu, professor of materials science and engineering and of chemistry at the University of California Berkeley, said:

People are now prepared to move into biodegradable polymers for single-use plastics, but if it turns out that it creates more problems than it’s worth, then the policy might revert back.

We are basically saying that we are on the right track. We can solve this continuing problem of single-use plastics not being biodegradable.

Researchers say the new tech should theoretically be applied to other types of polyester plastics and could lead to the creation of compostable plastic containers – which currently are made of polyethylene, a type of plastic called a polyolefin that does not degrade.

Dr. Xu added polyolefin plastics could be turned into higher-value products, not compost and she is now working on ways to transform recycled polyolefin plastics for reuse.

The most durable plastics have an almost crystal-like molecular structure, with polymer fibers aligned so tightly that water can’t penetrate them, let alone microbes that might chew up the polymers, which are organic molecules.

Dr. Xu’s idea was to embed nanoscopic polymer-eating enzymes directly in a plastic or other material in a way that sequesters and protects them until the right conditions unleash them.

In 2018, she showed how this works in practice. She and her team embedded in a fiber mat an enzyme that degrades toxic organophosphate chemicals, like those in insecticides and chemical warfare agents.

When the mat was immersed in the chemical, the embedded enzyme broke down the organophosphate.

Previously Dr. Xing designed molecules she called “random heteropolymers” (RHPs), that wraps around the enzyme and gently hold it together without restricting its natural flexibility.

They degrade under ultraviolet light and are present at a concentration of less than one percent of the weight of the plastic – low enough not to be a problem.

During this latest research, she encased the enzyme in RHPs and embedding billions of these nanoparticles throughout plastic resin beads that are the starting point for all plastic manufacturing.

Dr. Xing and her colleagues then showed that the RHP-shrouded enzymes did not change the character of the plastic, which could be melted and put into fibers like normal polyester plastic at temperatures around 170C (338F).

This is well below the normal temperature of the inside a compost heap, coming in at around 60C (141F) or higher – meaning the process would be easy with current composting methods.

It would also not break-down under slight dampness or if exposed to heat for short time so could even be used to make polyester clothing that would withstand sweating.

She said:

If you have the enzyme only on the surface of the plastic, it would just etch down very slowly.

You want it distributed nanoscopically everywhere so that, essentially, each of them just needs to eat away their polymer neighbors, and then the whole material disintegrates.

It turns out that composting is not enough – people want to compost in their home without getting their hands dirty, they want to compost in water.

So, that is what we tried to see. We used warm tap water. Just warm it up to the right temperature, then put it in, and we see in a few days it disappears.

The project is in part supported by the Department of Defense’s Army Research Office, an element of the US Army Combat Capabilities Development Command’s Army Research Laboratory.

Dr. Stephanie McElhinny, program manager with the Army Research Office, said:

These results provide a foundation for the rational design of polymeric materials that could degrade over relatively short timescales, which could provide significant advantages for Army logistics related to waste management.

More broadly, these results provide insight into strategies for the incorporation of active biomolecules into solid-state materials, which could have implications for a variety of future Army capabilities, including sensing, decontamination, and self-healing materials.

Dr Xu added:

It is good for millennials to think about this and start a conversation that will change the way we interface with Earth.

Look at all the wasted stuff we throw away: clothing, shoes, electronics like cellphones and computers.

We are taking things from the earth at a faster rate than we can return them. Don’t go back to Earth to mine for these materials, but mine whatever you have, and then convert it to something else.

The research paper detailing the new material has been published in the journal Nature.

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