‘Unique’ plastic as pure as the lotus flower, and as much a part of nature

“The Lotus,” researchers in 2008 wrote, “has been the symbol of purity for thousands of years; [contaminants] and pathogens are washed off the surfaces of Lotus and some other plants with rain or even dew.”

Now,  another group of scientists have developed a self-cleaning bioplastic, modelled on the lotus flower that is extremely water-repellent ('superhydrophobic') thanks to the rough surface of its leaves that repel water and dirt.

They say they are motivated to do something about plastic pollution, which, they note, is “recognised as a major environmental problem in many countries.” TRT World has also written about plastic pollution and the blight of microplastics that are tiny broken-down pieces of plastic which do not, however, completely disappear from nature.

According to the researchers, “academics have embraced research on bioplastics to discover newer high-end green materials,” yet the end-of-life environmental fate of such materials is “not adequately understood.”

The bioplastic developed at RMIT University in Melbourne, Australia repels liquids and dirt, the news release heralds, then breaks down rapidly once in soil.

RMIT PhD researcher Mehran Ghasemlou, lead author of the study published in Science of the Total Environment, says the innovative bioplastic could be the perfect fit for 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,” Ghasemlou says.

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

Ghasemlou enthuses about how nature was full of “ingeniously-designed” structures that could inspire researchers working to bring into existence “new high-performance and multifunctional materials.”

“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,” he says.

The bioplastic in question is composed of starch and cellulose, ingredients that are cheap and widely available. It is, according to the news release, also cheap to produce and easy to biodegrade in nature.

Ghasemlou says the fabrication process “does not require heating or complicated equipment and would be simple to upscale to a roll-to-roll production line.”

Fit to compost

An evidence review report prepared by Science Advice for Policy by European Academies called “Biodegradability of plastics in the open environment” points out that “most available plastics labelled as ‘biodegradable’ degrade only under specific conditions and can thus still cause harm to ecosystems.” The authors add that “plastics that are labelled ‘compostable’ are not necessarily suitable for home composting and may affect the quality of recyclates if compostable and conventional plastics are mixed in the recycling process.”

The authors of the “Biodegradability” report say that “failure of a biodegradable plastic to reach an appropriate receiving environment may lead to inefficient or incomplete biodegradation … with the associated environmental risks, and in these circumstances biodegradable materials are less likely to convey benefit over conventional plastics.”

Luckily, the new bioplastic created and described by Ghasemlou et al is at an advantage over other bioplastics, in that it “does not require industrial processes and high temperatures” to break it down, according  to the news release.

The new bioplastic “does not need industrial intervention to biodegrade,” and trials suggest it breaks down naturally and 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,” Ghasemlou says.

“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,” he continues.

Ghasemlou says the team’s ultimate goal 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.”

Inspired by nature

Lotus leaves, thanks to their surface structure, “composed of tiny pillars topped with a waxy layer,” are immune to dirt and water.

When the leaves get wet, the water drops do not stick to the surface but roll off, cleaning the plant as they slide off.

The RMIT team of science and engineering researchers put together starch and cellulosic nanoparticles to create the synthetic bioplastic, which they imprinted with a pattern reminiscent of the structure of lotus leaves. They then coated the printed pattern with a silicon-based organic polymer called PDMS (polydimethylsiloxane). They describe their workings in a separate study.

The news release reveals that the bioplastic “retains its self-cleaning properties after being scratched with abrasives and exposed to heat, acid and ethanol.”

Corresponding author, Professor Benu Adhikari, says the design “overcomes key challenges” of starch-based materials.

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

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

Thumbnail photo: The design of the self-cleaning bioplastic was inspired by the lotus leaf, which effortlessly repels water and dirt. Credit: RMIT University

Headline photo: Magnified image showing the pillared structure of a lotus leaf (left) and the new bioplastic (right). Images magnified 2000 times. Credit: RMIT University