SerPET uses raw and reclaimed PET plastics

Materials World magazine
25 Mar 2019

Irish Composites Centre Researcher, Walter Stanley, talks about a new method for producing a high-grade composite from plastic waste.

The world has a plastic waste problem and Ireland is leading the way. Eurostat figures show that Ireland creates almost double the amount of plastic packaging refuse as the European average, and 9kg more than the next highest ranking country, Luxembourg. So while EU citizens generate 31kg per person per year, on average, Ireland creates 61kg – a situation exacerbated by the number of countries closing their doors to the environmental waste trade.

‘A large proportion of this plastic is made up of single-use plastic bottles which, apart from polluting the landscape and seascape visually, also degrade over time and leach into the environment [in the form of chemicals and microplastics], creating many downstream problems for nature, animals and humans,’ said Irish Composites Centre (IComp) Researcher Dr Walter Stanley.

IComp is a partnership between the University of Limerick (UL), University College Dublin, Athlone Institute of Technology, and NUI Galway. The centre is hosted within UL’s Bernal Institute, which replaced the former Materials and Surface Science Institute, to function as a link between researchers and industry. It is a national technology centre funded by the government to liaise with Irish companies on competent materials. Recently, the centre gained €150,000 from Enterprise Ireland and €50,000 from the Environmental Protection Agency to research the recycling of polyethylene terephthalate (PET) single-use plastics.

In February 2019, IComp announced that it had found a way to reclaim and reuse valuable PET resources for applications such as car parts and tractors. Called SerPET, the material can include recycled or virgin PET waste to be formed into the self-reinforced polymer composite material. This high-tensile fibre has a high level of rigidity, strength and temperature performance, and is claimed to be more energy-efficient than making brand new plastics, while costing less than alternative recycled materials.

‘It is to make recycling more cost-effective and advantageous,’ said Stanley. ‘At the moment, we know some recyclers in Ireland do recycle PET, but it is going into low-end applications such as non-woven fillers for nappies. But if you can get a higher value added end-product, such as directional fibre composites into structural items, it will be more attractive to gain this high-grade recycled PET.’

Building up PET

‘We are not just recycling plastic into low-end applications. What we’ve done is recycled the PET into fibres – a standard carbon-fibre reinforced composite material, like a pre-preg – but the sheath around the fibre is also from PET, which can melt at a lower temperature than the fibre,’ Stanley explained. ‘So, if we thermoform it, the surrounding sheets will melt into the matrix but the fibres themselves remain intact. They still have their structure, strength and stiffness, but a composite will be realised. We go from cradle to grave to cradle again, so the composite, which is 100% PET, can be recycled at its end-of-life back into another composite, if required.

‘At the moment we are only working with PET. I know that polypropylene (PP) has been applied in this area, such as for the very expensive suitcases you can purchase in an airport, but the PET we want to explore will give us more expanded types of applications. Especially when we look at a sandwich structure with PET foam in its core, then we can also look at acoustic reductions and things like that, which may be of relevance to the automotive industry.

‘While we’re not going to restrict ourselves to automotive applications, we are looking towards semi-temporary structures for emergency situations, such that if there’s an earthquake, we can look at putting together semi-structural homes instead of tents that can be clicked together. Not only that, but also for electronic components, such as housings for laptops, tablets and sports equipment.

Recycling an old problem

There have been numerous programmes setup to exploit plastic waste resources, from the US Army melting it down to 3D-print car parts to Unilever blending it into thousands of detergent bottles – however, none of these reclamation projects have been sustainable on a large scale. So why is this new method different and how does it work?

‘It’s quite a convoluted process,’ Stanley said. ‘We take recycled pellets from a recycler and melt those down, then we extrude the fibres. Next we take those fibres and they have to be spun into a thread to weave, or another branch is try-layer tapes where we produce a tape of material. The two outer layers are the lower venting temperature materials and the inner is the directional material. Then they can be thermoformed into a composite material. There are many, many various forms for this to be realised.’

High-end applications are the goal, but for this you need a high-quality feedstock, putting a limit on already recycled plastics. ‘Virgin obviously has the optimal properties when you recycle because of contaminants – it’s very difficult to get 100% pure recycled PET,’ Stanley said. ‘It’s the way people throw out their bottles, so there are other impurities in there from the stickers and the bottlenecks, things like that. Therefore, some virgin PET must be added to get the original properties back up. Having said that, you can use fully recycled PET, but the properties would just be reduced and it would be of a lower structural quality.

‘What we have also done is looked into the sheeting material, and doping that with what we call susceptors. This is a more advanced manufacturing route but by using radio frequency heating it can affect the heating very, very rapidly, so you can have a really fast forming time. But it is a very expensive route. Some advanced European manufacturers might want to go down this route, but I don’t think it will translate into some economies, which may not have the money to invest in it.’

IComp lists the key features of SerPET as:

  • Polymer susceptibility that can be tailored to facilitate uniform rapid low-energy heating
  • Cycle time to manufacture of composite parts can be significantly reduced
  • Suitable for injection moulding, composite matrices, coaxial fibres, welding, hot-melt and thermally reversible adhesives
  • Staple or monofilament high tensile fibres may be spun
  • Fibres may be comingled with glass or basalt fibres for extra strength and stiffness, and
  • Metal-composite hybrid laminates or pre-consolidated pre-pregs can be developed for thermoforming, and susceptors may be strategically placed in panels to heat selected areas.

Rolling it out

Stanley said the technology could offer a solution for countries, such as India and China, to better manage their plastic waste. He said that countries struggling with plastic abundance could use this technology to exploit those raw resources, and recycle it into a stockpile of new materials.

‘It’s not like Lego, but it can be simply stuck together to make emergency housing,’ he said. ‘That’s my ultimate goal – to roll out this technology for others to use and reduce the scrap that is enveloping our oceans and beaches.’

But new production processes are rarely so straightforward and often come hand in hand with huge costs for building facilities, as well as labour and energy, which has been a sticking point for Ireland, as well as any potential developing nations. For successful and large-scale implementation, it will be crucial to first identify and close those gaps.

‘We’ve had to outsource all of our manufacture of the raw materials because we don’t have those sorts of material manufacturers in the Republic of Ireland,’ Stanley explained. ‘We go to Queen’s University Belfast, NI, and we go to fibre extrusion technologies in the UK to exclude the fibres, and to spin them and weave them. It would be bespoke, but there are countries around the world who have got weavers and so on.

‘The biggest issue [for wider adoption] would be the fibre extrusion. We don’t have that type of industry in Ireland, that’s why we’ve got to go to the UK. It would be quite a big step to allow an extruder to come and perform that stage. When we were looking around the world, there were places in India that do this, and I’m sure there are places in Germany and Turkey that also have this type of technology, but we wanted to keep this as close as possible to home, such that our researchers could go to Queen’s or to FET UK [a fibre extension technology company], within the British Isles.’

Circular economy?

According to Stanley, although the commercial benefits of SerPET will drive greater interest in the material’s use, among consumers and manufacturers, the project is firmly rooted in improving environmental credentials. ‘That’s our end goal,’ he said, ‘to make it more advantageous to recycle PET because Ireland is not so great in this.

‘PET is here. There’s nothing wrong with PET or plastic bottles. In an emergency situation, like Hurricane Katrina, how do you get fresh water to people? We still need to have plastic bottles – that is clear with every environmental disaster. Plus, despite having reusable bottles, which I think a lot of people have, people still use single-use plastic bottles. So we will always have those into the foreseeable future.’

Following success at laboratory level, SerPET must undergo 12 months of material testing to prove its properties. Stanley confirmed that over the next year, the team will develop a technical data sheet for publication, to show manufacturers the material’s properties, capabilities and applications. IComp is now aiming to license the technology for international use.