Recycled by-products key to ‘plastic of the future’

IFM researchers have designed a new plastic of the future – that not only improves in quality each time it enters the recycling process but diverts three waste by-products away from landfill.

The research paper, Inverse Vulcanisation of canola oil as a route to recyclable chopped carbon fibre composites, was published in the Sustainable Materials and Technologies journal.

The paper reveals how researchers combined recycled chopped carbon fibre with a polymer derived from elemental sulfur, a byproduct that’s in abundance within the mining industry, and waste canola oil, from fish and chip shops, to create a new thermoset plastic, that could be repeatedly separate from each other, mechanically or chemically, and recombined and processed into new composites.

‘There are two subcategories of plastics – thermosets and thermoplastics,’ lead researcher Dr Filip Stojcevski said.

‘Thermoplastics are the kind of plastics you see in water bottles and they work well because they can be remelted and recycled. The other type of plastic that’s used for aeroplanes is thermosets and once they are made, they can never be recycled.

‘We have discovered a new material that uses a different pathway to make a thermoset plastic – that can be recycled and used again and again.

‘By using these two byproducts to create a thermoset, we can hopefully one day replace half of the plastic that is on the market.’

The aim of the research was to ‘generate composites with improved physical properties, enabling their widespread use in high volume material applications’.

The research found that the introduction of 20 wt% carbon fibre was found to significantly improve tensile strength and modulus in iterative generations of recycling with tensile strength reaching a maximum of 909.1 kPa (+137.4%) and tensile modulus to 94.3 MPa (+160.1%) as compared to the initial introduction of carbon fibre.

‘The key findings we found were the material actually ended up getting better after two or three regenerations of recycling,’ Dr Stojcevski said.

‘Through the recycling process itself, the carbon fibre was getting better integrated with the plastic. If you think about penetration of the plastic into the fibre, it was getting better and better each time.

‘A material that gets better as you recycle – that’s an advantage.’

Building a new body of research

The research was an extension of the work being done by Professor Justin Chalker and his team at Flinders University, who were the first to discover how a polymer could be synthesised directly from elemental sulfur and plant oils such as limonene and canola.

‘Those two byproducts were being researched through a close association between us and Justin Chalker and his research group at Flinders University, who won a Prime Minister’s Prize for innovation in this field,’ Dr Stojcevski said.

‘No one had ever done this before and it seems to have such implications that the government recognised this as a huge breakthrough that wasn’t being researched.

‘At the time of this study we had seen what Justin Chalker at Flinder’s University had done and what he had shown is that you can this material and use it in wastewater remediation.

‘There is a lot of artisanal mining that puts mercury into the water streams in very low socioeconomic countries and of course that poisons the people.

‘This material is able to extract the mercury around those waterways and make it clean again.

‘The reason we got involved is because even though this material has these implications that are both economical, sustainable and can help regenerate the environment, it wasn’t useable in a sense that it wasn’t stiff enough.

‘Our real strength is in carbon fibre, which is stiff and could be used in association with these two waste products to make something that may be comparable to the existing materials. In this way we could create a usable, and socially impactful materials that is sustainable.’

Unlocking promising new materials

Dr Stojcevski says the material ended up having the same properties as cork and polyethylene, which with further research could make its way into construction and transportation industries. And he said this was just the beginning with his research group now exploring other ways to use the material. Already they have started researching other sustainable fibres, instead of carbon fibre, such as flax cotton, jute and hemp, which are also showing ‘promising results’.

‘PhD student Athulya Wickramasingha, who is a student of Professor Luke Henderson and who I help supervise, is looking at is an adhesive for metal joints,’ he said.

‘Interestingly she’s able to get good bonding strength using a very thin film of it between metal. Theoretically it could be implemented as a reusable adhesive glue, that wouldn’t have any material degradation. Research remains ongoing.

‘She’s also looking at it as a replacement of traditional plastics and composites, so imagine making carbon fibre that now has a full sustainable resin matrix, that when heated you can remove the carbon fibre, which makes recycling easier.’

Because the material has properties similar to cork, another potential use is shock absorption, or even flooring.

‘Imagine having a soft cushion floor that was completely made of waste by product and is structurally sound,’ he said.

‘We haven’t gone down that road yet, it’s still fundamental research, but the results seem promising.’