Ultrasound improves recycled plastics flow
Without highly efficient methods to separate post-consumer plastic waste, feedstock exhibits significant variations in physical properties and level of contamination. Scientists successfully addressed the batch-to-batch variability in flow properties due to the aforementioned issues with EU funding of the project 'Sensor-based ultrasonic viscosity control for the extrusion of recycled plastics' (ULTRAVISC). They exploited novel soft-sensor technology that essentially uses computer algorithms to draw inferences from process observations when the use of hard sensors is not possible. Information from the soft-sensor–monitoring technology is used to control the application of ultrasound to alter the viscosity of materials in the extruder. The system also used ultrasound to aid in filtering fine particulate contaminants. Process trials with a variety of dies and both virgin and recycled feedstock demonstrated the ability of the technology to reduce viscosity, maintain desired viscosity and increase throughput. ULTRAVISC technology will enable small and medium-sized enterprises (SMEs) to exploit the full potential of recycled plastic in the manufacture of new products. The large number of EU SMEs in the field can now continuously monitor and control the viscosity of extruded materials to minimise waste while producing higher-quality products. Better control has even opened the door to new markets, including products with thinner walls than previously possible. As consumers continue to recycle more and more plastic materials, SMEs can now take better advantage of it, increasing their competitive position while preserving natural resources.