US scientists have developed a biodegradable plastic that breaks down in just a few weeks when exposed to heat and water.
The breakthrough, made by researchers at the University of California, Berkeley, has the potential to transform the plastics industry if it can be applied at scale.
Biodegradable plastics have been championed as one possible solution to the problem of plastic pollution, but some products labelled ‘biodegradable’ or ‘compostable’ do not actually break down in typical composting conditions, and can create problems if sent for recycling.
“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,” said Ting Xu, a UC Berkeley professor and author of the research paper, published in the journal Nature.
“We are basically saying that we are on the right track. We can solve this continuing problem of single-use plastics not being biodegradable.”
One of the most commonly-used compostable plastics is polylactic acid (PLA) – a synthetic polymer derived from plant-based materials, which is designed to biodegrade in industrial compost but can last as long as regular plastics if it ends up in landfill.
Now Professor Xu and her team have invented a way to make these compostable plastics break down within just a few weeks using heat and water.
The molecular structure of the most durable plastics is almost crystal-like and so strong that the polymer fibres are impenetrable to water, or indeed the microbes that might break them down.
But the UC Berkeley team’s breakthrough came when they embedded polyester-eating enzymes into polyester as the material is made.
Billions of these nanoscale particles were embedded in the resin beads that are the starting point for plastic manufacturing. Xu compares this process to embedding pigments in plastic to color them.
The enzymes were protected by a simple polymer wrapping, which is released and degrades on exposure to heat and water, allowing the enzymes to break down the plastic into its original building blocks. In the case of PLA, this reduces it to lactic acid, which feeds the soil microbes in compost.
“If you have the enzyme only on the surface of the plastic, it would just etch down very slowly,” Xu said. “You want it distributed nanoscopically everywhere so that, essentially, each of them just needs to eat away their polymer neighbours, and then the whole material disintegrates.”
Triggered by water and a little heat, 80 percent of the modified PLA fibres degraded entirely within about one week, whilst the process was even faster at higher temperatures, such as those employed in industrial composting.
The majority of compostable packaging products on the market today – such as this range of compostable carrier bags from leading UK manufacturer Polybags – are designed to disintegrate within a matter of weeks and fully biodegrade within a few months in industrial composting conditions.
Whilst these products offer a handy waste management solution to those with a food waste collection service at their disposal – which ends up in industrial composting – Xu’s discovery has the potential to go one giant step further, with products that degrade in just warm water.
“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,” said Xu.
“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 full research paper is available to read at Nature.com.
Images courtesy of UC Berkeley.
