Lotus-like bioplastic repels liquid and dirt

Researchers at RMIT University have developed a self-cleaning bioplastic that is sturdy, sustainable and compostable. Described in the journal Science of the Total Environment, the innovative plastic repels liquids and dirt — just like a lotus leaf — then breaks down rapidly once in soil.

According to lead author Mehran Ghasemlou, a PhD researcher at RMIT, nature is full of ingeniously designed structures that could inspire researchers striving to develop new high-performance and multifunctional materials. With this in mind, he said, “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.”

Lotus leaves are renowned for having some of the most water-repellent surfaces on Earth and are almost impossible to get dirty. The secret lies in the leaf’s surface structure, which is composed of tiny pillars topped with a waxy layer. Any water that lands on the leaf remains a droplet, simply rolling off with the help of gravity or wind. The droplets sweep up dirt as they slide down, keeping the leaf clean.

To make their lotus-inspired material, the RMIT team first synthetically engineered a plastic made of starch and cellulosic nanoparticles. The surface of this bioplastic was imprinted with a pattern that mimics the structure of lotus leaves, then coated with a protective layer of PDMS, a silicon-based organic polymer.

Tests show the bioplastic not only repels liquids and dirt effectively, it also retains its self-cleaning properties after being scratched with abrasives and exposed to heat, acid and ethanol. Corresponding author Professor Benu Adhikari said the design overcomes key challenges of starch-based materials, noting, “Starch is one of the most promising and versatile natural polymers, but it is relatively fragile and highly susceptible to moisture.

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

While biodegradable plastics are a growing market, most require industrial processes and high temperatures to break them down. Ghasemlou noted, “There are big differences between plant-based materials — just because something is made from green ingredients doesn’t mean it will easily degrade.”

The RMIT bioplastic does not need industrial intervention to biodegrade, with trials showing it breaks down naturally and quickly in soil. Ghasemlou said, “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.”

Furthermore, the bioplastic is made from cheap and widely available raw materials to keep production costs low and support rapid biodegradability. The fabrication process does not require heating or complicated equipment and would be simple to upscale to a roll-to-roll production line.

“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,” Ghasemlou said.

“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.”

Ghasemlou is currently working with a bioplastic company, which is evaluating further development of these novel water-repellent materials. The RMIT research team is keen to collaborate with other potential partners on commercial applications for the bioplastic.

Image credit: ©stock.adobe.com/au/kaymotec

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