Abstract
With the increase the worldwide consumption of vehicles, end-of-life vehicles (ELVs) have kept rapidly increasing in the last two decades. Metallic parts and materials of ELVs can be easily reused and recycled, but the automobile shredder residues (ASRs), of which elastomer and plastic materials make up the vast majority, are difficult to recycle. ASRs are classified as hazardous materials in the main industrial countries, and are required to be materially recycled up to 85–95% by mass until 2020. However, there is neither sufficient theoretical nor practical experience for sorting ASR polymers. In this research, we provide a novel method by using S-Band microwave irradiation together with 3D scanning as well as infrared thermal imaging sensors for the recognition and sorting of typical plastics and elastomers from the ASR mixture. In this study, an industrial magnetron array with 2.45 GHz irradiation was utilized as the microwave source. Seven kinds of ELV polymer (PVC, ABS, PP, EPDM, NBR, CR, and SBR) crushed scrap residues were tested. After specific power microwave irradiation for a certain time, the tested polymer materials were heated up to different extents corresponding to their respective sensitivities to microwave irradiation. Due to the variations in polymer chemical structure and additive agents, polymers have different sensitivities to microwave radiation, which leads to differences in temperature rises. The differences of temperature increase were obtained by a thermal infrared sensor, and the position and geometrical features of the tested scraps were acquired by a 3D imaging sensor. With this information, the scrap material could be recognized and then sorted. The results showed that this method was effective when the tested polymer materials were heated up to more than 30 °C. For full recognition of the tested polymer scraps, the minimum temperature variations of 5 °C and 10.5 °C for plastics and elastomers were needed, respectively. The sorting efficiency was independent of particle sizes but depended on the power and time of the microwave irradiation. Generally, more than 75% (mass) of the tested polymer materials could be successfully recognized and sorted under an irradiation power of 3 kW. Plastics were much more insensitive to microwave irradiation than elastomers. With this method, the tested mixture of the plastic group (PVC, ABS, PP) and the mixture of elastomer group (EPDM, NBR, CR, and SBR) could be fully separated with an efficiency of 100%.
Highlights
Since the beginning of the 21st century, polymer technologies have developed rapidly and been implemented in many fields of industry, which has significantly reformed the behaviors both in Sensors 2018, 18, 1355; doi:10.3390/s18051355 www.mdpi.com/journal/sensorsSensors 2018, 18, 1355 production and consumption [1,2,3]
We provide a novel method by using S-Band microwave irradiation together with 3D scanning as well as infrared thermal imaging sensors for the recognition and sorting of typical plastics and elastomers from the automobile shredder residues (ASRs) mixture
All of the polymer scraps were tested to pass through the microwave irradiation field three times with the irradiation power of 3 kW, 6 kW, kW,9respectively
Summary
Since the beginning of the 21st century, polymer technologies have developed rapidly and been implemented in many fields of industry, which has significantly reformed the behaviors both in Sensors 2018, 18, 1355; doi:10.3390/s18051355 www.mdpi.com/journal/sensorsSensors 2018, 18, 1355 production and consumption [1,2,3]. Since the beginning of the 21st century, polymer technologies have developed rapidly and been implemented in many fields of industry, which has significantly reformed the behaviors both in Sensors 2018, 18, 1355; doi:10.3390/s18051355 www.mdpi.com/journal/sensors. In the vehicle industry, huge amounts of polymer materials including plastics and elastomers have been utilized to take the place of metallic materials in vehicles in order to lighten the weight of cars and further reduce fuel consumption as well as the emissions of pollutants and greenhouse gases [4,5,6,7,8]. China has had a rapid development both in vehicle production and consumption. In 2014, the total vehicle production reached about 24 million, which made China the largest automobile producer and consumer in the world [9,10,11]
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