How to finally replace the plastic bag

After Australian states and territories introduced plastic bag bans, supermarkets like Woolworths have recently begun offering alternatives such as paper bags. But much to the chagrin of eco-conscious consumers, it’s hard to go into a supermarket these days and not still be frustrated by the overwhelming presence of plastic. Whether it’s plastic bags for the vegetables or bananas and apples wrapped in the stuff, it’s clear plastic packaging isn’t disappearing any time soon.

But the fact that environmentally friendly alternatives aren’t more readily available, is not for a lack of trying. “There are synthetic polymers which have properties that are great, but they’re much more expensive,” says Graeme George, Emeritus Professor at Queensland University of Technology. One of those is known polyhydroxybutyrate, or PHB. It’s among a class of plastics which are bio-derived and biodegradable. Because PHB is made by microorganisms it decomposes when buried in soil.

“We’ve had this plastic since the 1970s, so coming up to 50 years now and it hasn’t been able to be fully commercialised,” Prof George explained. “Why has it taken 50 years? It’s the same question of cost.”

Traditional plastic bags are made from ethylene, derived from petroleum or natural gas which does not degrade easily and as a result, they mostly end up in landfill. But the process of making them is highly automated, cheap and their properties are perfect for their purpose. Despite all the work that has been done, biodegradable alternatives are still more expensive by a factor of about 10.

Prof George, who has made a career in macromolecular and materials chemistry and studying the environmental issues of plastics, says there is one material that has been getting a lot of attention due to its potential to replace standard plastic bags at a low cost: starch.

“We’re more familiar as starch as a food stuff than anything else,” he conceded, but starch-based polymers could provide a cheaper source of biodegradable plastic material, although so far it lacks the sturdiness of regular plastic bags.

Nonetheless, such alternatives have been trialled in Australia recently. Last year, light-weight “compostable” bags for fruit and vegetables made from 98 per cent corn starch were trialled in two south Australian supermarkets.


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