Biodegradable plastic bags, cutlery and coffee towel lids may seem like a victory for the environment, but they often introduce more problems than solutions.
Despite being advertised as “green,” many of these plastics last as long as their conventional counterparts break down into home compost and landfill, causing more contamination in soils and waterways.
Many are also not recyclable, and can be destroyed only by industrial composting under high temperatures.
Now, a team of researchers at the University of California at Berkeley has finally created a biodegradable plastic that almost completely disappears into home compost after a few days, just by adding heat and water.
The new material includes built-in enzymes that chew the plastic into non-toxic molecules without leaving traces of harmful microplastics.
The researchers’ study was published today in Nature.
“Enzymes are really just catalysts by nature to carry out reactions,” said scientific material and co-author of the study, Ting Xu.
Biodegradable is not equal to compostable
A 2015 study estimated that only 9 percent of the world’s plastics are recycled, and most of them end up in landfills.
Australia is slightly better, with around 18 per cent of our plastic waste ending up in recycling facilities.
Biodegradable plastics – which disintegrate into water, carbon dioxide or organic material with the help of microorganisms – have been proposed as an environmentally friendly alternative to oil-based species.
Many of these plastics are made of polyesters, such as polylactic acid (PLA) and polycabrolactone (PCL).
They consist of tightly packed chains of molecules called polymers.
This makes them durable, but also difficult for water and soil microbes to penetrate enough to degrade them.
While the chemical composition of these traditional materials is technique biodegradable, they can be demolished only in industrial composting facilities under strictly controlled temperatures and conditions, said material scientist Hendrik Frisch of the Queensland University of Technology, who did not participate in the study.
“Under other conditions such as soil or marine environments, these materials often show similar durability as their conventional fossil fuel-based companies, causing significant environmental damage and pollution,” Dr. Frisch said.
In response to this problem, the federal government launched a National Plastics Plan earlier this year that aims to eliminate plastics that “do not meet compostable standards”.
The power of enzymes
Professor Xu is researching how to use enzymes to treat pollution and make materials more biodegradable for more than a decade.
In 2018, Professor Xu and her team created fibroids with embedded enzymes that break down toxic chemicals, found in insecticides and chemical warfare agents, into water.
In their new study, Professor Xu and colleagues separated billions of polyester-eating enzymes through PLA and PCL beads, which are used early in the manufacturing process to create plastic products.
By melting these beads, they formed the material into filaments and sheets for testing.
To prevent these enzymes from collapsing before they had a chance to do their job, the researchers coated them with custom polymers to keep them embedded in the plastic.
Without this supporting polymer coating, the enzymes could only partially chew through the molecular chains, leaving contaminated microplastics behind.
But wrapped in the lining, the enzymes were able to crush these large molecules down to their building blocks, similar to breaking down a pearl necklace.
“The enzyme does not leave the plastic [behind], “Professor Xu said.
“Even when the plastic degrades into very small pieces, the enzymes continue to function.”
Plastics pull a disappearing action
When the team added their enzyme polyesters to home soil compost with some tap water, 98 percent was transformed into their individual buildings in just a few days.
The small molecules left behind were harmless, with the enzymes transforming PLA into lactic acid, food for soil microbes.
The enzymes ate the plastics even faster under industrial composting conditions, with PCL breaking in just two days at 40 degrees Celsius, and the PLA disappeared within six days at 50C.
While the “programmed degeneration” offers a promising approach to treating plastic pollutants, Dr. Frisch says more research is needed to find out if the technique works with other types of plastic.
Recombining the residues of the degraded plastics into new products may also require a special recycling facility, he added.
“Implementing several cycles of doing and undoing will be something that needs to be explored in the future.”
Professor Xu said the approach could one day be applied to produce more biodegradable products, from polyester clothing to biodegradable glue in phones and electronics.
“We want to work with industry to really promote this so that it can be found in the grocery store and on your counter.”