Plastics: green, strong, robust – could we have it all?

A*STAR scientists have developed a material that is biodegradable, strong and robust – a combination that was only an aspiration till now – bringing them one step closer to making plastic products greener.

Team lead Dr Li Zibiao (left) and senior specialist Jayven Yeo (right)

Biodegradable polymers

A way to make plastic products eco-friendly is to make them with biodegradable polymers instead of today’s petroleum-based ones.

Conventional petroleum-based polymers are not compostable, relying on a natural process to degrade, which often takes more than a thousand years to complete. When in a marine environment, such as when plastic bottles end up in the ocean, petroleum-based polymers could endanger marine life.

Polylactic acid (PLA) is a potential candidate for replacing petroleum-based polymers in plastics, as it is biodegradable and compostable. It can degrade within days into carbon dioxide and water under controlled conditions, offering a more sustainable alternative.

PLA materials today, however, are not good enough to make plastic products. Although strong, they tend to be brittle, given the trade-off between strength and flexibility. Their barrier performance must also be improved.

The new technology

A team of scientists and engineers at A*STAR’s Institute of Materials Research and Engineering (IMRE) has developed a new type of PLA material that is 15 times more robust than existing ones, yet just as strong, overcoming the trade-off thought to be inevitable.

The solution, the team revealed, was to create a highly interconnected 3D polymer network.

“What surprised us,” said lead researcher Dr Li Zibiao, 38, a senior scientist and head of the advanced sustainable materials department at IMRE, “was how malleable the new plastic is. We usually see such behaviour only in metals.”

The material is very flexible – it can stretch 120 per cent without breaking, compared to less than 10 per cent in existing PLA materials, giving it the robustness that plastic products need.

It is also biodegradable, being a combination of PLA (over 90 per cent) and green additives.

That the material is malleable and biodegradable is significant, for malleable polymers are often non-biodegradable.

“It was interesting,” Dr Li said, “to see the way the 3D polymer network interacted with a fibrillar (small fibres) bridge that we put in. That’s not one but two mechanisms at work.”

“That’s what makes the material tough.”

Published in the journal Advanced Functional Materials in April 2020, Dr Li’s discovery was the first report of PLA that could be bent, twisted and folded at room temperature.

“Innovation is the name of the game,” said IMRE’s executive director Professor Loh Xian Jun, himself a polymer chemist. “Against the backdrop of climate change, science and technology play an important role in the search for solutions for a more sustainable planet.”

Applications

Dr Li has two latest prototypes: a thin, translucent film, and a dog-bone shaped specimen (pictured on top left of photo). The former is useful for packaging solutions, and the latter, electronic applications.

Dr Li's prototypes (top row) compared with existing PLA materials, which are brittle (bottom row)

His team continues to improve the properties of the enhanced PLA material for use in plastic products, such as barrier performance, which in packaging could prolong a product’s shelf life.

“We are in talks with fast-moving consumer goods companies to further develop the material for packaging applications,” Dr Li said.

“While we develop materials that are more degradable, such as this polymer, we must also reduce the carbon footprint of manufacturing such materials,” added Professor Loh.

The innovation opens up new possibilities for green electronics, such as a laptop that is green, strong, yet robust. As researchers continue to uncover new ground in this area, their efforts will bring us closer to reaching that goal.