Wrapped in shellfish

Materials World magazine
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1 Sep 2018

A new material made from food waste could be a biodegradable alternative for food packaging, as Ellis Davies reports.

A material made up of a mix of crab shells and tree fibres has been developed for use in food packaging, comprising the two most abundant biopolymers – cellulose and chitin. Researchers at Georgia Institute of Technology, USA, aimed to produce a thin film that could rival the highest grades of polyethylene terephthalate (PET), showing up to a 67% reduction in oxygen permeability in comparison, meaning that it will keep food fresher for longer.

Carson Meredith, Professor of Chemical and Biomolecular Engineering at Georgia, told Materials World, ‘We have been working on cellulose nanomaterials for around eight years [...] As an offshoot to this project, we were trying to think of additional renewable sources of polymers, and came upon chitin. Not many people were looking at it, so we saw an opportunity to demonstrate how it could be used, and we viewed it as something that could compliment cellulose.’ Meredith and his team were intrigued by the idea of using a food waste product such as chitin in a food packaging application, as it could be composted after use to make a circular product.

They extracted chitin from crab shells in fibre form, where they are in the nanoscale, and began to look at ways to deposit them as thin films. They settled on spray coating – a simple industrial process in which water based suspensions of fibres are sprayed onto a substrate.

Polylactic acid (PLA) was used as the base material because it is biodegradable, and is sourced from biomaterials, meaning that it can be composted. Also, PLA doesn’t have the oxygen barrier properties needed for food packaging, and the team saw this as an opportunity to improve the material.

‘It’s the oxygen sealing properties that are the key primary properties that you want for food packaging,’ says Meredith. Researchers found PLA’s mechanical properties to be sufficient, and the resulting film is optically transparent, which allows it to look like any other food packaging film. Meredith says that the desired water barrier properties are still in progress.

The benchmark

PET is commonly used in the production of food packaging, from water bottles to thin films. However, ‘there are a wide range of PET grades, so the oxygen permeability can vary over a factor of five times,’ says Meredith. The films produced perform as well as the best PET grades, but are currently not as cost effective.

‘In the immediate future it would not be very cost effective because the raw materials, especially the chitin, are not being produced industrially at an appropriate scale,’ says Meredith. ‘That is going to change, in my view, and there are already some companies, such as fishery byproduct recycling company Tidal Vision, USA, looking at ways to produce chitin for products like packaging. I would compare the challenge here to be similar to what it has been seen in the cellulose nanomaterial domain, where there are now major corporations beginning to produce cellulose nanofibres in tonnes per day, which has started to drive the cost down. I think something similar will happen to chitin.’

Looking forward, researchers will continue their work on the project. ‘This is an on-going research product, and we continue to investigate the oxygen properties to improve them so that less material is used – this is one way to control cost,’ says Meredith. The team is also looking at rudimentary process designs to try to estimate the manufacture cost that would exist today, and ways to monitor the quality of the chitin during its manufacture, which is an important part of scaling the process.