Impurities in waste plastics, as well as the wide variety of materials they contain, limit the amount that can be retrieved through recycling. An innovative EU-funded project has come up with an ultrasonic technique that enables recyclers to recover more plastic, at lower cost … and it is fully automated. A commercial solution could lead to savings worth millions of euros.
To the untrained eye, recycling almost appears to be like some kind of alchemy, that medieval art which sought to transform base metals into gold. For instance, you may put soft drink bottles in at one end of the process and produce plastic chairs and tables at the other end.
Recycling plastics has many environmental and economic advantages. With dwindling global supplies of oil, recycling offers a powerful means of reducing the amount of petroleum (currently standing at around 8% of global production) required to manufacture plastics, the production of which is growing steadily. In fact, the amount of plastic produced in the first decade of this century is believed to have exceeded all that was produced in the previous one.
Plastic waste, which has a tendency to spread to even the remotest environments, can take centuries to decompose, and is potentially harmful to the environment, human health and wildlife. Although reducing the amount of disposable plastic products manufactured offers the most sustainable way forward, recycling is also a powerful tool.
But recycling faces many challenges. The complex structure of plastic polymers makes the mixing of different plastics difficult or can result in weaker materials, and requires greater amounts of energy in the production process. The upshot of this is that a lower proportion of plastic waste is recycled compared with other materials: 21.3% in the EU against 80% of newspapers. However, it should be pointed out that Europe also uses plastic waste as an energy source, and so, together, energy recovery and recycling use up more than half of the Union's plastic waste.
Going with the flow
The variability in the quality of inputs also leads to major fluctuations in the viscosity, i.e. the 'thickness' of the melted raw materials as they flow through the production process, requiring constant adjustment to the temperature and other variables if a consistent quality is to be maintained. This presents a major challenge for extrusion, i.e. the process of pushing the melted plastic through a special die which cuts or shapes it into the desired form, resulting in significant waste.
The EU-funded project 'Sensor-base ultrasonic viscosity control for the extrusion of recycled plastics' (Ultravisc) has broken the mould when it comes to extruding products from recycled plastic. The two-year project sought to improve the recycling of post-consumer plastic waste by compensating for impurities and variations in the physical properties of recycled feedstock.
The way Ultravisc does this is through the use of sensors to regulate the flow and viscosity of the feedstock during the extrusion process. It employs a closed-loop system to monitor the conditions of the recycled polymers and applies ultrasonic energy to the melt as and when required.
"The ultrasonic technology is used to control the flow of the plastic through the production line and to control the properties of the plastics, resulting in the production of a more consistent product," explains Dr Paul Beaney, the technical manager at Cherry Plastics Group which coordinated the project.
"Ultrasonic technology had never been integrated into recycling technology before, so building the ultrasonic modulator was a big challenge," he adds. But the consortium of eight partners from six EU countries – drawn from industry and academia – managed to pull it off successfully to create an automatic system that does not require human interference.
Recycling for all
Ultravisc is an intelligent and fully automated process. "Because the knowledge is built into the system, it does not need operators who are highly skilled or experienced," notes Dr Beaney. This advance has the potential to open up plastic recycling to a wider group of actors, and not just highly specialised companies.
Another benefit of this fully automated melt-flow system is that it has halved the response time compared with traditional temperature-control methods. And, it can regulate the flow and viscosity at far lower temperatures, thereby boosting the overall efficiency of the recycling process.
"Ultravisc also allows you to use recycled products in places where it was not previously possible, and enables you to use more waste plastics in the process, thereby improving the environmental friendliness of the recycling process," Dr Beaney adds.
The project participants are exploring how best to commercialise the technology – whether to do it themselves or seek out partners. A working lab prototype has been built which has been fully tested, and the team is now in the process of building a full-scale unit which can be used on the large extruders at Cherry Pipes, based in Dunganno, Northern Ireland (UK). When implemented fully, and depending on how it is commercialised, Ultravisc is expected to reduce waste by about 2%, down time by around 5%, and lower energy consumption by 5% when used on extruders. This could amount to millions of euros in savings if the technology is taken up by enough recyclers.