The modern world’s addiction to plastic shows no sign of ending, with forecasts indicating that demand for the material is likely to rise steeply in the coming decades.
As a result, efforts to design and produce less harmful alternatives have ramped up.
Cutlery, bottles and plates can now be made out of plant material, and some even degrade into fish food.
But can they replace the need for traditional plastic?
Is biodegradable the answer?
Given the problems created by conventional plastics, mostly generated from fossil fuels, is the answer to be found in biodegradable alternatives?
Starch, cellulose (plant fibres), biologically derived polymers and proteins are the starting points for various biodegradable plastics, including packaging materials. Some biodegradable plastics are compostable, meaning that they turn into a nutrient-rich substance.
“There are many types of compostable plastics,” said Dr Teresa Domenech, associate professor in industrial ecology and the circular economy at University College London.
“The most common ones are polylactic acid derived. The feedstock is starchy products such as sugar cane, corn starch … but they can be derived from a variety of biomaterials, including agricultural waste.”
Researchers are investigating potential new materials, as evidenced by a study published in June by scientists at the Dubai campus of the Indian university Bits Pilani.
The scientists found that a composite of starch, cellulose, chitin (which can be obtained from fungi, for example) and date seed extracts could be useful as a food packaging film.
Starch is widely available from plants including wheat, corn and potatoes but, on its own, tends not to prevent the growth of microorganisms that cause food to spoil.
With the date seeds extract included, the film was better able to protect the fruit from deteriorating.
“Addition of extracts from date seeds to the prepared composite film imparted antioxidant and antimicrobial properties, which when used for fruit wrapping suggested that the freshness of the fruit was retained for a much longer period,” the researchers wrote in Food Bioscience.
When conditions are optimal, the film degraded in composting soil in five to seven weeks.
In another example, scientists in China recently found that a mix of cellulose nanofibres and part of the sweetcorn stalk called the corn straw core was a potential food packaging material because it resisted ultraviolet light and was not water vapour permeable.
The researchers’ paper in the journal Food Hydrocolloids described corn straw cores as “by far the most readily available” type of crop waste.
Breaking down the truth
While such results may appear to suggest that biodegradable packaging could be the answer to society’s plastic problem, “there are all sorts of caveats”, according to Prof Phil Purnell, a professor of materials and structures at the University of Leeds in the UK.
Key among them is that materials that are compostable typically break down under a specific set of circumstances.
“There’s a perception if it says biodegradable it will rot down. That’s not the case at all,” Prof Purnell said.
“If you bury them in the garden, after a year they will still be there.”
According to a 2020 Greenpeace East Asia report, Biodegradable Plastics: Breaking Down the Facts, 83 per cent of biodegradable plastic used for packaging is “industrially compostable”.
This means that for it to turn into compost, it must be processed in particular conditions, with humidity carefully managed and temperatures above 50°C.
If compostable material is put into a regular compost bin or thrown on the ground, it will probably not degrade because conditions will not be hot enough.
Another issue with biodegradable plastic, such as packaging, is that it can contaminate recycling streams for regular plastic waste.
As a result, biodegradable plastic needs to be kept separate from non-biodegradable plastic, which is not easily done.
“At the moment we have to be cautious in terms of replacing conventional plastic packaging with compostable materials because there’s not a clear route for the end of life of these plastics,” Dr Domenech said.
“They are perceived by the public as low carbon or low impact, but they don’t necessarily have to be low carbon or low impact.”
Are we better off sticking to regular plastic?
Indeed, at the moment it may be more straightforward to process conventional plastic than biodegradable plastic.
“Packaging materials like PET [Polyethylene terephthalate] are basically recyclable through plastic mechanical recycling and there are already structures. In some cases, these have a clear route and there is a closed loop,” Dr Domenech said.
A closed loop means that the plastic can be turned into another product of the same type, rather than something different.
There is also concern that biodegradable plastics may encourage consumers to continue to buy products wrapped in single-use plastics because there is a perception that the environmental impact is reduced. It is a concern for the environmental organisation Greenpeace.
“Our position is clear on this: We consider these technologies false solutions that do not stop the plastic crisis. There is no way to throw away, the solution is to reduce and reuse,” said Dania Cherry, of Greenpeace Mena.
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