The scientists have developed the first truly biodegradable plastics that break down in just a few weeks when exposed to heat and water.
Most ‘compostable’ plastics as they are called today are made of polyester called polylactic acid, or PLA, and do not actually break down during typical composting.
As a result, they are often disposed of in landfill – where they last as long as traditional ‘forever’ plastics.
However, researchers from the United States have incorporated polyester-eating enzymes, protected by special polymer wrap, into polyester plastics as they are made.
When exposed to heat and water, the enzymes are released by their packaging and work to break down the plastic into its constituent parts.
In the case of PLA, the plastic is reduced by the enzyme proteinase K to lactic acid – which can be used to feed the soil microbes found in compost.
The enzyme wrapper also degrades under ultraviolet light, the team explained.
Furthermore, the enzyme-coated plastics do not produce microplastic pollutants when it breaks down – with 98 percent degrading into small molecules.
The scientists have developed the first truly biodegradable plastics that break down in just a few weeks when exposed to heat and water. Pictured: the modified plastic containing polyester eating enzymes (left) breaks down into regular compost (right)
MAKE BIODEGRADABLE PLASTICS
In their study, Professor Xu and colleagues focused on plastics made of the polyester ‘polylactic acid’.
However, they said, it should be possible to apply the same principle to other types of polyester plastics.
This, the team says, may allow the creation of compostable plastic containers – replacing some polyethylene that won’t degrade.
Professor Xu said she believed it would be better to turn polyethylene and other so-called polyolefin objects into higher value products at the end of their original life.
To this end, the team is now working on ways to transform recycled polyolefin plastics for reuse.
‘People are now ready to move to biodegradable polymers for single-use plastics,’ says paper writer and materials scientist Ting Xu of the University of California Berkeley.
‘But if it seems to create more problems than it’s worth, then the policy could come back,’ he added.
‘We’re basically saying we’re on the right track. We can solve this ongoing problem of not being biodegradable single use plastics. ‘
The problem with conventional plastics is that they are inherently designed not to break down – which is great for normal use, but not environmentally beneficial later on when thrown.
In fact, the most durable plastics have almost a crystal-like molecular structure, with polymer fibers aligned so tightly that exterior polymer-eating microbes cannot enter.
Professor Xu’s and colleagues’ approach circumvents this problem by adding the microbes to the plastic before use.
The key to the researchers’ innovation was to develop a way to keep the polyester-eating enzymes from collapsing – which is what proteins typically do when extracted from their native environment, such as a living cell.
The wrappers they used to protect the enzymes were made of molecules called ‘random heteropolymers’, which hold the proteins together lightly without restricting their natural flexibility.
These molecules degrade under ultraviolet light and are present at a concentration of just 1 percent by weight in the plastic – which the researchers say is low enough not to cause a problem.
To make the biodegradable material, wrapped enzyme nanoparticles are incorporated into their billions in the resin beads which are the starting point for all plastic manufacturing – similarly pigments are used to color plastic.
‘If you only have the enzyme on the surface of the plastic, it would etch down very slowly,’ explained Professor Xu.
‘You want it to be distributed nanoscopically everywhere so that they all need to eat away their polymer neighbors, and then the whole material decomposes.’
In their study, the team showed that the heteropolymer randomly wrapped enzymes did not change the basic properties of the plastic – which could be dissolved and extruded into fibers at temperatures of around 338 ° F (170 ° F).
To make the biodegradable material, wrapped enzyme nanoparticles are incorporated into their billions in the resin beads which are the starting point for all plastic manufacturing – similarly pigments are used to color plastic. ‘If you only have the enzyme on the surface of the plastic (as the top shows), it would etch down very slowly,’ explains Professor Xu. ‘You want it to be distributed nanoscopically everywhere (bottom) so they all need to eat away their polymer neighbors, and then the whole material breaks down’
Under high temperature industrial composting conditions of 122 ° F (50 ° C) the modified PLA was found to degrade completely within six days.
Another modified plastic – this one based on polycaprolactone with lipase enzymes – broke down faster, however, degrading in just two days at 104 ° F (40 ° C).
Lipase and proteinase K are cheap and easily produced enzymes.
The researchers are also looking to randomly program the heteropolymers so that the plastic breakdown can be prevented part way, which would allow the plastics to be re-melted for other purposes.
According to the team, the modified polymers do not degrade at low temperatures or during short humid periods – meaning they could be used to make clothes, for example, that could survive sweat and be washed on moderate temperatures.
Similarly, soaking in water for three months at room temperature did not cause the plastic to deteriorate – unlike lukewarm water.
‘It seems that composting is not enough – people want to compost at home without getting their hands dirty, they want to compost in water,’ said Professor Xu.
‘So, that’s what we tried to see. We used warm tap water. Heat it to the right temperature, then put it in, and we see in a few days that it disappears. ‘
One modified plastic (left) – this one based on polycaprolactone with lipase enzymes – broke down in just two days in water heated to 104 ° F (40 ° C), as shown on the right
‘It’s good for millennials to think about this and start a conversation that will change the way we interact with the Earth,’ said Professor Xu.
‘Look at all the wasted things we throw away: clothes, shoes, electronics like mobile phones and computers. We take things from the ground faster 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,’ he recommended.
With their initial study completed, paper writer Aaron Hall – a former doctoral researcher at Berkeley – has formed a spin-out company to further develop these biodegradable plastics.
The full findings of the study were published in the journal Nature.
URBAN FLOODS ARE FLOOR MICROPLASICS IN OCEANS FASTER THOUGHT
Urban flooding is causing microplastics to be flushed into our oceans even faster than previously thought, according to scientists looking at pollution in rivers.
Waterways in Greater Manchester are now so heavily contaminated by microplastics that particulates are found in all samples – including even the smallest streams.
This pollution is a major contributor to contamination in the oceans, researchers discovered as part of the first in-depth catchment-wide study anywhere in the world.
These debris – including microbeads and microfibres – are toxic to ecosystems.
Scientists tested 40 sites around Manchester and found that each waterway contains these tiny toxic particles.
Microplastics are very small pieces of plastic debris including microbeads, microfibres and plastic pieces.
It has long been known that they enter river systems from several sources including industrial effluent, storm water drains and domestic wastewater.
However, although it is thought that about 90 percent of microplastic contamination in the oceans originates from land, little is known about their movements.
Most rivers surveyed had about 517,000 plastic particles per square meter, according to researchers from the University of Manchester who conducted the in-depth study.
Following a period of major flooding, the researchers re-sampled at each of the sites.
They found that contamination levels had decreased in most of them, and that floods had removed about 70 percent of the microplastics stored on the river beds.
This shows that flooding can transfer large amounts of microplastics from urban river to the oceans.