Single-use packaging is a necessary part of health and medicine, providing safety and sterility, but this innovation from engineers at Monash University promises to help reduce the environmental impact of these requirements.
Challenges abound when it comes to bioplastics. No generally-accepted definition exists for the material; it is simply characterised as being biodegradable, biobased, or both. Both these terms have many interpretations, and the wide range of polymer types confuse end-users. Most bioplastic currently ends up in landfill, adding to one of the main problems it is meant to solve.
However a team from Monash University has created a framework for a novel type of biodegradable plastic by converting food waste sugars into polyhydroxyalkanoates (PHA) biopolymers, and then blending those polymers to produce sustainable, compostable ultrathin films with tunable properties.
According to the CSIRO the PHA family of biodegradable polymers holds the most promise for commercial viability to replace single-use packaging because of its ability to break down in various environments.
The Monash study, published in BMC, was led by Edward Attenborough and Dr Leonie van ‘t Hag from the Department of Chemical and Biological Engineering. Attenborough said that being able to tailor these natural plastics for different uses opens the door to sustainable alternatives in packaging, especially where they can be composted along with food or agricultural waste.
Two breakthroughs in one study
“The very interesting thing is that we’ve grown two different strains of bacteria separately, then extracted the polymers. The polymers displayed a broad range of chain lengths and random monomer incorporation, consistent with the biosynthetic nature of PHA copolymers.
“And then we blended them at different variations to look at how miscible these blends are, and how we can tailor and tune the plastic that we’re getting. We found that adding these increased chains gave us a more flexible, plastic material that’s a bit more stretchy and less brittle.”
Attenborough said that it is not only the mechanical properties that can be tuned, but also the melting points. And this led to another first by the research team.
Using FTIR spectroscopy to take ester carbonyl bands and then fitting the bands with Gaussian curves, Attenborough and van ‘t Hag were able to quantify polymer crystallinity. Higher polymer crystallinity corresponds to more ordered molecular packing and reduced chain mobility, while lower crystallinity is associated with more amorphous and flexible polymer regions.
“So it’s not just exciting that we have blended these plastics to tune them, but we have also developed a technique for very quick testing of the samples to see the crystallinity instead of running them through more expensive and complex machinery.”
A product with full circularity
The polymers were created by feeding two soil-dwelling bacteria – Cupriavidus necator and Pseudomonas putida – a carefully balanced “diet” of sugars with the right blend of salts, nutrients and trace elements. Once the microbes fattened up, they began stockpiling natural plastic inside their cells, reaching cell lengths up to 30 microns. The scientists then “milked” these plastics out using solvents, cast them into ultrathin films about 20 microns thick and tested their stretchiness, strength and melting behaviour.
The aim was to create full circularity in a plastics ecosystem. A lot of biodegradable plastics are fossil-fuel based, and some that are plant-based compete with our food production systems. To avoid both these sources, the team used food waste sugars to produce the bio-based polymer. The product also needed to be home compostable and fully marine biodegradable to be an effective replacement for single-use plastic.
“There’s been a bit of work on films, but not much on really thin films. We want to look at 20 micron thin films to see if we could solve this problem of dual circularity for ultra film or a plastic product.”
Currently, the bioplastic has potential as biomedical film with multiple melting points, or as a mulch film because it composts as it degrades in the soil.
Multiple potential uses
The next step is to expand the source of waste used to create the polymer, including to carbohydrates and fats, and optimising use cases.
“This would be a great solution for food waste, and something that could work really well on a farm. For all their fruit or food that is not good enough to go on shelf, this would be a way to use them,” Attenborough said.
It could also be implemented directly at processing sites. For example, at a frozen food company, where large amounts of potato waste are generated, this approach could enable full circularity, turning that waste into the packaging used for their own potato products.
It is not just packaging the team is considering. Attenborough said they are also looking at biomedical applications, with a study from the authors published in 2024 on nanoparticles for drug delivery.
The team is collaborating with industry partners including Enzide and Great Wrap through the ARC RECARB and VAP hubs to develop biodegradable packaging and medical solutions with potential commercial applications.