Science & Nature

May 1, 2017

FROM SHRIMP TO PLASTIC

For some time, during the 20th century, plastic was considered one of Mankind greatest inventions. Ladies and gentlemen from all over the world, used them as a prize, when shopping. Then it became a headache, just before becoming public enemy number one. 

First of all, the terrifying numbers. Take a sit and don't be too scared.

Every year, the United States only, generates 34 million tons of non-recycled plastic. Thus, the Atlantic Ocean won itself its own continent of plastic waste to rival with the Pacific Garbage Patch (and there are four more trash vortexes around the world). In the North Pacific Ocean, fish ingest an estimated amount of 24 thousand tons of plastic every year.

Conventional polythene plastic, made from fossil fuels, lasts between 500 to 1000 years before decomposing. Considering, human being has been using this material for over 40 years, we can calculate the amount of plastic bags there are in the oceans. And we're only talking about regular plastic bags.

Fortunately, some countries are aware of this total ecological disaster and they are taking measures to solve this huge planetary problem. For instance, the United Kingdom has been working hard to create a biodegradable bag industry and, the United States, are starting to ban plastic bags and other forms of plastic materials. Other countries like Taiwan, South Africa and Bangladesh have already banned plastic bags.

One could say: plastic bags are most convenient when shopping and there are already bioplastics made from plants.

Indeed. However, this is not a solution for developing nations, such as Egypt, where most cultivation goes entirely for food and cotton production and processing.

And that's why, researchers and bioengineers at Nile University, in Egypt, are developing a process to turn dried shrimp shells, which would be thrown away, into thin films of biodegradable plastic. Their goal is to obtain a new biodegradable material which will be used to produce reliable eco-friendly grocery bags and other kind of food packaging.

The funds came in September 2016 and, since then, Dr. Nicola Everitt, material engineering professor from the University of Nottingham, in the United Kingdom, has been leading the research team in Cairo, Egypt. So far, they discovered that out of two pounds (less than a kilogram) of shrimp waste, they can produce as many as 15 bags. This could seam short numbers, but given the country imports 3,500 tonnes of shrimp every year, which produce 1,000 tons of shell waste, the numbers are quite appealing.

After six months of the two-year project, the team has managed to create a thin, clear prototype of plastic, using Chitosan, a substance which can be found in the shells of many crustaceans.

Chitosan is already known to scientists. Recently, the biomedical industry has been working with this substance in order to use it in tissue engineering, drug delivery and wound healing.

Processing the shells

For the time being, the researchers buy the shrimp shells from restaurants, supermarkets and local fishermen at low prices. Don't forget we're talking about food waste.

Afterwards, the shells go into a laboratory for the chemical treatment.

The chemical process is quite simple. The shells are boiled in acid to dissolve the calcium carbonate, which is what makes the shells brittle. And then, in order to remove the protein molecules, the obtained substance is boiled, once again, in an alkali solution. This will induce the mixture to turn it into a polymer in the form of flakes. These flakes, can then, be processed into a thin plastic film using conventional manufacturing methods.

Processing the shrimp shells into Chitosan is particularly attractive. The substance is, not only, biocompatible, but it also has antimicrobial and antibacterial properties. In addition, the plastic film absorbs oxygen, making it very suitable for the food industry as it prolongs the shelf life of many products.

Furthermore, people with shellfish allergies don't react to Chitosan.

According to Dr. Nicola Everitt, "so far, the team has only produced small samples of the film and the project is not yet ready to go into commercial large scale production, but the team is working hard to develop properties that would allow the material to go into widespread use".

Right now, the team in Egypt is working to optimize chitosan extraction process, which takes about three days to complete, but "that might come down when the process has gotten a bit more streamlined", Dr. Everitt added.

This process is being worked out, also at Harvard's Wyss Institute for Biologically Inspired Engineering, Massachusetts, United States. For the American researchers, there is no reason why plastic can't be replaced with other biodegradable material. Their option is aiming for the production of Shrilk, made out of Chitosan.

The tests performed in the United States show the material breaks down within few weeks of being thrown away and provides nutrients for plants.

Chitin, the principle of Chitosan, is the second most abundant organic material on the planet and it can also be found in fungal cells, insect exoskeletons and butterfly wings.

Going back to Dr. Nicola Everitt: 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 dump sites. It could also make exports more acceptable to a foreign market within a 10 to 15 year' time frame".

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