Material Scientists Set Out to Beat Plastic Packaging on 3 Fronts – They Succeeded
They’ve brewed up a plastic alternative that is transparent, nonabsorbent (i.e., won’t get soggy) and disappears in two months—and for a bonus, it’s edible.
By Emma Bryce
Packaging with all the strength and resilience of plastic, but without its environmental impacts: this would seem too good to be true. Yet a group of researchers say it’s exactly what they have created: a plastic alternative that’s not only transparent and strong, but also completely edible and fully degradable after two months.
The team of researchers from the University of Hong Kong built on previous research into bacterial cellulose, a sheet-like substance made of tight-knit cellulose fibers that’s produced by the activity of certain bacterial species. The substance is renewable, non-toxic, and it degrades in the environment.
Yet for all these benefits, it has one weakness: its huge sensitivity to water, which makes it unsuitable for storing wet goods or functioning in humid environments.
This design challenge set the researchers on an experimental path to test different ingredients and recipes for making a superior cellulose composite. They started with a productive bacteria species Komagataeibacter xylinus, placing it in a growth medium of tea and sugar. Into this mix, they stirred protein isolates extracted from soybeans, which they hoped would strengthen its resilience and other mechanical properties.
Then after seven days of fermentation they took the bacterial cellulose film that had formed, and plunged it into a pool of calcium alginate, a biodegradable ingredient that increases transparency of the substance and crucially, adds water- and oil-resistant properties. They also mixed in a compound called polyethylene glycol which helped to bind the ingredients and acted as a plasticizer which gives regular plastic its bendy qualities.
After drying out the film, the researchers had a robust raw material that they could fashion into different products for testing. Starting with a bag designed to store oily ingredients like cereal and crisps, they found that the packaging kept the contents crisper against humid exterior conditions than conventional bacterial cellulose bags. It also performed comparably to single-use polyethylene plastic bags that are the ubiquitous default worldwide.
And when the researchers plunged straws made out of their new material into everything from water to coffee and fizzy drinks, they discovered that while they did eventually bend a little, they were far more water-resistant and lasted far longer than the paper straws that have become everyday plastic replacements, despite their tendency to disintegrate.
Tests also showed that the tensile strength of the cellulose composite outperformed both paper and low-density polyethylene plastic that’s ubiquitous in single-use packaging. But encouragingly, these resistant qualities don’t seem to hold out for long — which is the major design challenge in conventional plastic that drives its detrimental persistence in the environment. In fact, in experiments where the researchers buried their plastic alternative in soil, they say the material broke down within one to two months.
They also claim that their alternative gets around another problem of conventional plastic in the ocean which can float around for decades, poisoning and starving sea creatures who mistake it for food. The new cellulose product is non-toxic to consume — and while even so, you ideally wouldn’t want animals filling their stomachs with any substance other than their natural food, the short lifespan of this plastic alternative would hopefully limit creatures’ exposure to this product in the wild.
What’s more, the researchers see routes for more sustainable production by using food waste streams as the raw materials to nourish the cellulose-secreting bacteria.
Worldwide, a striking 40% of plastic waste is packaging, most of it single-use and much of it escaping into the environment where it lives on for decades. Many now recognize that production caps are the only way to limit the sheer scale of single-use plastic production. Yet it’s likely that we’ll still be dependent on some plastic products going forward, and for those we need to design better alternatives that don’t pose such an existential planetary risk.
As the researchers see it, their discovery is one ingenious way to move us towards that goal. “This research serves as a reminder that natural raw materials may already possess the necessary characteristics to perform beyond the functions of plastic packaging.”
Ngai et. al. “Edible, strong, and low-hygroscopic bacterial cellulose derived from biosynthesis and physical modification for food packaging.” Journal of the Science of Food and Agriculture. 2023
Source: Anthropocene magazine (7 July 2023)