Self-cleaning bioplastic modelled on the lotus plant

Researchers have developed a new bioplastic that’s sturdy, compostable, and cleans itself, modelled on the miraculous qualities of the lotus leaf. 

The innovative plastic repels liquid and dirt, and then breaks down rapidly when buried in soil, according to studies published in Science of the Total Environment and Applied Materials and Interfaces.

Mehran Ghasemlou, lead author of the studies and a PhD researcher at RMIT University, says the new bioplastic could be ideal for use in fresh food and takeaway packaging.

“Plastic waste is one of our biggest environmental challenges but the alternatives we develop need to be both eco-friendly and cost-effective, to have a chance of widespread use,” says Ghasemlou. 

“We designed this new bioplastic with large-scale fabrication in mind, ensuring it was simple to make and could easily be integrated with industrial manufacturing processes.”

The new research is a classic example of bio-inspiration – taking inspiration from the ingenuity of evolution to solve classic technological problems. 

“We’ve replicated the phenomenally water-repellent structure of lotus leaves to deliver a unique type of bioplastic that precisely combines both strength and degradability,” says Ghasemlou.

Compostable plastics?

The new plastic is naturally compostable, which sets it apart from most mainstream bioplastics which require industrial processes to break down.

This bioplastic, on the other hand, breaks down quickly in soil.

“There are big differences between plant-based materials – just because something is made from green ingredients doesn’t mean it will easily degrade,” says Ghasemlou.

“We carefully selected our raw materials for compostability and this is reflected in the results from our soil studies, where we can see our bioplastic rapidly breaks down simply with exposure to the bacteria and bugs in soil.

“Our ultimate aim is to deliver packaging that could be added to your backyard compost or thrown into a green bin alongside other organic waste, so that food waste can be composted together with the container it came in, to help prevent food contamination of recycling.”

Lotuses: a lean, mean, self-cleaning machine

Lotus leaves, among their many strange and mythic attributes, are almost impossible to get dirty. That’s thanks to their supremely water-repellent surface which, at the micro-level, is composed of tiny pillars topped with a waxy layer.

Any water that lands on a lotus leaf will remain a droplet, and simply roll off as compelled by gravity or wind. Those droplets sweep up any dirt from the leaf’s surface as they go, keeping it remarkably clean.

To make their self-cleaning plastic, the RMIT researchers synthetically engineered a plastic made of starch and cellulosic nanoparticles. The surface of the plastic was then imprinted with a pattern that mimicked the columns of a lotus leaf, before being coated with a protective layer of PDMS, a silicon-based organic polymer.

Tests found that the bioplastic not only repels liquids and dirt effectively, but also retains its self-cleaning properties after being scratched with abrasives and exposed to heat, acid and ethanol. That makes it particularly useful for the food industry.

Corresponding author Benu Adhikari says the design overcomes many of the challenges of starch-based plastics.

“Starch is one of the most promising and versatile natural polymers, but it is relatively fragile and highly susceptible to moisture,” Adhikari says.

“Through our bio-inspired engineering that mimics the ‘lotus effect’, we have delivered a highly effective starch-based biodegradable plastic.”