How machines can now identify and separate plastic wastes
While it may seem like a benign material, there are a bunch of reasons why different kinds of plastics are harmful to our health, let alone the environment. Plastic has a very specific leeching property. This means the small pieces which are not visible to our naked eyes have the potential to enter soil and water. This in turn affects the food we eat and other important parts of our lives. Microplastics are plaguing the environment in a way that exists even in the air we breathe. The issue is rampant, and out of control. For the well-being of living beings on earth, it is therefore essential to study how plastics affect health and what their harmful properties are. Not only this, but it is also equally important to identify and segregate them into ways in which they can be contained. Industries can do better if they become more aware of the effects and can take necessary action to stop or at least control plastic consumption.
Given the characteristic feature, plastics are notably inexpensive, lightweight, and durable, which can readily be moulded into a variety of products that find use in a wide range of applications. As a result, the production of plastics has increased markedly over the last 60 years. However, current levels of their usage and disposal generate several environmental problems. Around 4% of world oil and gas production, a non-renewable resource, is used as feedstock for plastics, and a further 3 to 4% is expended to provide energy for their manufacture. A major portion of plastic produced each year is used to make disposable items of packaging or other short-lived products that are discarded within a year of manufacture. These observations alone indicate that our current use of plastics is not sustainable. In addition to this, because of the durability of the polymers involved, substantial quantities of discarded end-of-life plastics are accumulating as debris in landfills as well as in natural habitats worldwide. Recycling, therefore, is one of the most important actions currently needed to reduce these impacts and the method alone represents one of the most dynamic areas in the plastics industry today.
Recycling provides opportunities to reduce oil usage, carbon dioxide emissions, and the quantities of waste requiring disposal. It aids in waste-reduction strategies, chiefly in the reduction of material usage through downgauging or product reuse, the use of alternative biodegradable materials, and helps with using energy recovery as fuel. While plastics have been recycled since the 1970s, the quantities that are recycled vary geographically, according to plastic-type and application. Recycling of packaging materials has seen rapid expansion over the last decades in many countries, even globally. Advances in technologies and systems for the collection, sorting, and reprocessing of recyclable plastics are creating new opportunities for recycling, and with the combined actions of the public, industry, and governments it may be possible to divert most plastic waste from landfills to recycling over the next decades.
The recent research from the Aarhus University, Denmark, demonstrated for the first-time computer vision technology, which can be used to differentiate between a wide range of plastics according to their chemical composition. Applied on an industrial scale, this could enormously increase the rate of plastic recycling. This new technology, developed by researchers from the department of biological and chemical engineering at Aarhus in collaboration with Vestforbænding, Dansk Affaldsminimering ApS, and Plastix allows for differentiation between 12 different types of plastic which constitute many households’ plastic types. The plastics are PE, PP, PET, PS, PVC, PVDF, POM, PEEK, ABS, PMMA, PC, and PA12. Plastics that exist in the world today are combinations of many materials (polymers) with varying chemical compounds and additives, containing pigments or fibers, depending on their core application. This makes it extremely difficult to tell the difference between types of plastic, making it hard to separate and recycle them. More than 90% have not been recycled. With this technology, the camera allows for the separation of plastic-based litter on a purer chemical composition than what exists today. It, therefore, opens new opportunities for plastic recycling. It has already been piloted and will be implemented this year.
“With this technology, we can now see the difference between all types of consumer plastics and several high-performance plastics,” said Professor Mogens Hinge, who is heading this study. “We can even see the difference between plastics that consist of the same chemical building blocks, but which are structured slightly differently.” He further spoke of the hyperspectral camera being used, in the infrared area, which leverages machine learning to analyse and categorise the type of plastic to be directly loaded on the conveyor belt. The plastic then is separated into different types. The researchers believe that the breakthrough will have a huge impact on all plastic separation.
The separation of plastic from various types of waste streams remains one of the major problematic processes. The sorting of plastics is a very essential step in different waste management techniques. Manual sorting is suitable when plastic components are present in large amounts, but it is a labour-intensive process. In the automated sorting technique, NIR (near-infrared) offers a great advantage among all wave sorting techniques but is not suited for dark-coloured plastic and can be used on transparent bodies. In air sorting, lighter particles are separated from heavier ones based on specific gravity. In electrostatic sorting, method materials are separated based on electrostatic charge. In the float-sink separation technique, the plastics are in a fluid that has a density in between the materials making it possible for less dense material to float and heavier to sink. Plastics are currently separated using near-infrared technology or via density tests, that is they are tested based on floating or sinking in water. These methods can separate certain plastic fractions, like PE, PP, and PET but not with the same accuracy as this new technology, and therefore not with the chemical purity in the composition. This kind of technology is vital for boosting the recycling rate of plastic waste.
Plastix CEO Hans Axel Kristensen also commented: “The technology we’ve developed in collaboration with the university is nothing short of a breakthrough for our ability to recycle plastics. We look forward to installing the technology in our processing hall and starting in earnest on the long journey towards 100% utilisation of waste plastic.” Plastic must be at least 96% pure by polymer type to be recycled according to conventional industrial processes. This means that the plastic must be separated into an almost pure product in terms of chemical composition. Hinge says that bringing in new technology and adding it will enable the continuation of refined data to indicate it may soon be possible to differentiate even further between polymer and additive types.
The study has been published in the scientific journal Vibrational Spectroscopy. Using the new technology, “we are now a big step along the way”, says Associate Professor Mogens Hinge, who stresses that the technology is continuously being developed and that data indicates it may be possible to differentiate even further between polymer types and additives before long. The hyperspectral camera technology has been developed in cross-disciplinary collaboration, including BSc and MSc engineering students and researchers at the Department of Biological and Chemical Engineering at Aarhus University, as well as experts from the participating companies. Additionally, the research is part of the Re-Plast project, which is being funded by the Innovation Fund Denmark with DKK 22.7 million. The project is being headed by the Department of Biological and Chemical Engineering at Aarhus University. Other participants are the Department of Electrical and Computer Engineering at Aarhus University, Vestforbrænding, Dansk Affaldsminimering and PLASTIX.
While plastic pollution is majorly prevalent in landfills, it is not the only place where plastics cause pollution. As a matter of fact, more than 90% of all waste that is floating on the surface of oceans is plastic. That can be approximated to about 46,000 pieces of plastic per square mile. Additionally, over a million seabirds and over 100,000 marine animals are killed by plastic pollution every year. Even more shocking is that 44% of seabird species, 22% of crustaceans, a growing range of fish species, and all sea turtles are known to have plastic in their bodies. Plastic pollution is a major problem which must be dealt with immediately. If we don’t stop it now, we’ll only create a bad environment for future generations.
References:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2873020/
https://www.sciencedirect.com/science/article/pii/B9780081026762000025
https://techxplore.com/news/2022-01-breakthrough-plastic-machines-distinguish.html
