Metrological challenges of plastics recycling

Plastic waste volumes are globally expected to increase from 260 million tons per year (2016) to 460 million tons per year by 2030. In Europe, industrial and private end-users consumed about 55 million tons per year in year 2018. Only about 17 % of this was collected to recycling, and the global share was even smaller. However, increasing recycling of plastics will have an important role in achieving the goals of EU Green Deal that aims making Europe climate neutral in 2050. Today, plastics is mostly recycled into secondary raw material by applying a mechanical recycling process, i.e. collected plastics waste is shredded/grinded, sorted, washed, dried and extruded. The basic structure of the secondary raw material remains the same as in the collected waste. Due to inhomogeneity, produced secondary raw material can only be used in limited number of applications. Significant advancement is expected from chemical recycling in which waste is converted into fuels or petrochemical feedstock. Pilot plants applying chemical recycling are running in several countries and developments for scaling up are on-going. Measurements play an important role in running plastics recycling: many sensor technologies are applied in sorting material and controlling process. Due to variety of materials in waste, measurements are challenging and quality control is difficult. On the other hand, material volumes are large and increasing, which calls for efficient on-line measurement and quality control methods. Research is needed for developing new measurement technologies and appropriate metrology tools for quality control that enable efficient process operation and ensure reliability of data for fair trade. This paper reviews the current sensor technologies used in plastics recycling and studies needs for new measurement and calibration technologies.