Researchers at RMIT University in Melbourne, Australia, have developed a sturdy bioinspired plastic that can repel both liquid and dirt. The innovative self-cleaning bioplastic has potential applications in environmentally friendly fresh food and takeaway packaging as it stops moisture getting in and spoiling products, and is also compostable once finished with. With plastic waste and pollution being such a huge environmental challenge, the bioplastic is produced from inexpensive starch and cellulose, both widely available raw materials that help to keep production costs low.
Although the majority of biodegradable and compostable plastics need considerable industrial processes and high temperatures to break them down, this material does not depend on heating or complicated equipment to biodegrade as the compostable raw materials break down naturally and quickly in soil. As reported in the journal Science of the Total Environment [Ghasemlou et al. Sci. Total Environ. (2022) DOI: 10.1016/j.scitotenv.2021.152684], the design also overcomes some key challenges of starch-based materials. Although starch holds promise as a versatile polymer, it is quite fragile and very susceptible to moisture.
Lotus leaves are one of most water-repellent surfaces in nature due to their surface structure of tiny pillars topped with a waxy layer. Water that lands on the leaf stays as a droplet and just rolls off due to gravity or wind. These droplets pick up any dirt as they move down, keeping the leaf clean. The new bioplastic mimics that surface structure. The team synthetically engineered a plastic made of starch and cellulosic nanoparticles, with the surface of the bioplastic being imprinted with a pattern that mimics the structure of lotus leaves before being coated with a protective layer of a silicon-based organic polymer.
Tests show the bioplastic repels liquids and dirt effectively, and retains its self-cleaning properties even after being scratched with abrasives and exposed to heat, acid and ethanol. As lead author Mehran Ghasemlou 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”.
One application is in stopping unwanted rainwater from reaching a crop, or in food or beauty packaging applications. The bioplastic could also one day be used as packaging that is home-composted or put with other organic waste so that food waste can be composted together with the container it came in. The team now hope to further develop and test the material to reduce the costs of scaling up, as well as to improve the ease of printability and meet the regulations for use in food applications.
“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”Mehran Ghasemlou
Magnified image showing the pillared structure of a lotus leaf (left) and the new bioplastic (right). Images magnified 2000 times. Credit: RMIT University.