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Plastic from prawns: science is beating the bag scourge

polymer

Turning a waste problem into part of the solution is something researchers at the University of Nottingham and the Nile University in Egypt are hoping to achieve. They are currently just over half way into a two-year project trialling how to turn prawn shell waste into biodegradable shopping bags and also how to turn it into food packaging that can extend the life of products.

The study is aimed at helping to address Egypt’s waste issues because around only 60-65% of the country’s waste is collected – the remainder is simply dumped on streets, in canals and rivers, in open areas or at illegal dump sites, usually in plastic bags.

Researchers are looking at how to use chitosan (see box), which is extracted from prawn shells, to make biodegradable shopping bags. According to their calculations, 1kg of prawn shell waste could be used to produce 10-15 bags. In a second phase of the project, they also hope to investigate whether prawn shell waste can be turned into active polymer food packaging that can help extend the life of food.

Nicola Everitt, associate professor for materials engineering at the University of Notting­ham, is leading the research in the UK, alongside professor Irene Samy from Nile Uni­versity. The idea for the project came about after a research visit by Samy – who was already doing work on chitosan membranes for a dif­ferent use – to Everitt’s lab, followed by supper at her house. When there, Samy was impressed with the array of household collection bins she saw and a conversation ensued.

Everitt looked into the waste situation in Egypt and discovered that a large proportion of waste is simply not collected, which explained Samy’s reaction to household bins in the UK. She adds that because around 60% of this uncollected waste is organic, it rots away, but it is generally contained in plastic bags which do not deteriorate in short timescales.

“What sparked [the idea for the project] was learning how little of [Egypt’s] waste is actually collected and how little of the plastic packaging is degradable,” says Everitt. “There is a big prob­lem with plastic waste collecting both on land and in the sea…and [Egyptians] don’t really have any culture of degradable packaging.

“The use of a degradable biopolymer made of prawn shells for carrier bags would lead to lower carbon emissions and reduce food and packaging waste accumulating in the streets or at illegal dump sites.”

While in the UK the introduction of charg­ing for single-use plastic carrier bags has led to a culture change whereby shoppers bring their own bags and therefore use fewer of them, Everitt says this is not the case in Egypt which is “behind the curve” in this area.

The research project is sponsored by the Newton Fund and the Newton-Mosharafa Fund grant, designed to promote economic development and social welfare in partnering countries.

everitt

everitt

Everitt, pictured, explains: “The Newton Fund grant is particularly geared towards helping a partner country – some of our objec­tives are to help the government there with awareness of reuse and recycling – that is obviously a good long-term aim. But the idea of the bags was that if Egyptians are still using plastic bags, it would be better to use a degradable plastic than a synthetic one which is just going to hang around [in the environment].”

So far, the research team in Egypt has been processing the shell waste and producing the chitosan films, while the team in Nottingham has been characterising them in the lab, “and trying to decide what is a sensible formulation and structure of them” Everitt explains.

“They have made some films and we are testing the first generation. Then the idea is that, based on the knowledge we get from that, we then perform another iteration and try to improve the product.”

One of the project’s objectives is to chart rates of degradation of the chi­tosan film: “The film produced straight, without fillers, is very suscep­tible to degradation by UV and I think humidity might also play a part. So it will be more a case of making sure the films do not degrade too fast to make the bags not usable rather than the other way around.”

Everitt adds that the hope is to assess levels of degradation in high levels of sunlight, as well as when the film is buried. “Initially, we will con­centrate on the ‘with sunshine and lots of oxygen’ [scenario], based on the fact that the problem sparking this was plastic blowing about in piles and piles [in the open environment].”

The second thrust of the grant will be to look at developing active poly­mer packaging. This is packaging that controls the atmosphere around food. Everitt says this stage of the project has not yet started but it would inves­tigate the use of nano-chitosan from prawn shell waste as a packaging material.

“You can make nano-particles – once you have got the chitosan you can use another pro­cess and make nano-sized particles of it,” she explains. But because of the miniscule size of the particles, there could be issues of migration to the body which would need investigation.

“We could do preliminary testing, but that would probably require another grant or another research programme later on to get that to a usable product,” she adds. “By the end of this grant, we are hoping to have a prototype bag, which is the ‘cheap and cheerful’ end of it, and maybe have made some progress towards the active polymer packaging.

“When I last went to Egypt, we had some meetings with fruit harvesting and packaging companies who might be interested in the idea of having an envelope or large package that the fruit goes in while it is transported. So it wouldn’t be the packaging that is actu­ally over the fruit in the supermarket, it would be an envelope around the fruit while it was transported to the supermarket to keep it in the right conditions for ripening.”

She emphasises that this is at ‘pre­liminary discussion phase’ only and there are no results in the lab yet for this part of the project to back it up or otherwise. However, such an applica­tion would mean that factors such as the transparency of the film would not matter as much because it would not be consumer-facing, and there would be fewer concerns with nano-particles migrating to the product.

While the chitosan material made from prawn shell waste could be recy­cled from a technical point of view, because of the lack of recycling infra­structure in Egypt, this is an unlikely end route. Instead, the bags would be designed to degrade in the shortest amount of time to eliminate their pres­ence in the environment.

Everitt says the research has gener­ated interest from countries with large prawn processing industries such as the US and Thailand, where there is interest in using their own waste to create such a product. It would be in such countries that chitosan films would potentially be viable in the future.

Part of the research includes consid­ering the commercial viability of the technology. Everitt says initial calcula­tions suggest there would need to be a system to recycle the strong acids and alkalis used in the process, as well as potentially factoring in environmental benefits.

While the project’s prototype bag would not be produced on a commer­cial machine, part of the study will include talking to people who cur­rently produce polyethylene (PE) blown bags. This would be to discuss trying to use chitosan commercially and whether there are any barriers to using it. The hope is that chitosan could be used as a direct replacement for PE in exist­ing production facilities. If successful, Everitt says it could take 10-15 years for such a system to come to fruition.

film made from lab grade chitosan

film made from lab grade chitosan

Film made from lab grade chitosan

What is chitosan and how is it made?

Chitosan is a man-made polymer derived from the organic compound chitin, which is extracted from prawn shells.

Extraction is done first using acid to remove the calcium carbonate ‘backbone’ of the crustacean shell, and then alkali to produce the long molecular chains which make up the biopolymer.

The dried chitosan flakes can then be dissolved into solution and a polymer film made by conventional processing techniques.

Chitosan is a promising biodegradable polymer already used in the pharmaceutical industry due to its antimicrobial, antibacterial and biocompatible properties.

 

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