Ethan Clarke
Plastic is a defining material of the modern world, used in everything from food packaging to children's toys. However, plastic waste has severe impacts on the environment, health, and economy. As a result, plastic recycling is vital in managing waste and creating a more sustainable future. One of the key steps in the plastic recycling process is separating recyclable plastic. This involves sorting plastic by type, colour, thickness, and usage, which can be done at Material Recovery Facilities (MRFs) and Plastic Recovery Facilities (PRFs) using advanced sorting machines and techniques like optical sorters, infrared, x-ray, and other cutting-edge sensors. Accurate separation ensures the integrity of the finished, recycled plastic and enables a higher recycling rate.
| Characteristics | Values |
|---|---|
| Where is the plastic collected from? | Homes, businesses, schools, and other institutions |
| Where is the plastic sent for separation? | Material Recovery Facilities (MRF) and/or Plastic Recovery Facilities (PRF) |
| What are the different types of plastics? | PET, HDPE, PP, PVC, PE |
| How are plastics separated? | By colour, thickness, usage, and chemical composition |
| What methods are used to separate plastics? | Optical sorters, wet processes like sink-float separators, infrared, x-ray, and other cutting-edge sensors |
| Why is it important to separate plastics? | To maintain the integrity of the finished, recycled plastic and to meet local demands for specific polymers |
| How much plastic was recycled in 2019? | 9% of 368 million tonnes |
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What You'll Learn
Sorting by type
Plastic waste collected from homes, businesses, and recycling centres is sent to Material Recovery Facilities (MRFs) and/or Plastic Recovery Facilities (PRFs) for sorting. MRFs handle plastic and non-plastic waste, while PRFs sort plastic by type. Sorting plastic by type is crucial as different plastic polymers have distinct characteristics, and mixing them would alter these characteristics. The outcome of each recycling process should ideally be a single type of plastic polymer rather than a mixture.
PRFs use various sorting techniques and equipment such as optical sorters and NIR sensors to distinguish between different types of plastics. For instance, NIR sensors scan objects from around 12 inches away, using known NIR spectral images to identify the plastic type. Jets of air are then used to separate the different plastic types in different directions. Another method is the wet process known as a sink-float separator, where a tank is filled with water, and high-density plastics sink while low-density plastics float.
Some facilities have advanced, fully automated sorting machines that can separate plastics by colour and type, as well as handle the removal of contaminants like metals, wood, rubber, and foil. These contaminants can be removed through electrostatic methods, while soiled or dirty materials can be de-dusted and sieved.
The sorting process is vital to maintaining the integrity of the finished, recycled plastic. Impurities in the new resin can result in a lower-grade plastic that may not be recyclable. Additionally, economic factors, such as local demand for a particular polymer, influence the relevance of sorting plastics before they are sold for recycling.
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Sorting by colour
The recycling process for plastic waste typically begins with the collection of plastic from homes, businesses, and local recycling centres. This plastic is then sent to Material Recovery Facilities (MRF) which separate plastic and non-plastic materials. The next step involves sending the plastic to a Plastic Recovery Facility (PRF) for further sorting into different types of plastic. This step is crucial to maintaining the integrity of the finished, recycled plastic as different plastic polymers have distinct characteristics and end-products. For instance, plastic lumber and plastic bottles are two distinct end-products of the recycling process.
Sorting plastic by colour is an important part of the recycling process. Optical detection systems are used to separate colours, with operators able to remove items by touching them on a screen. Ultraviolet light is also used to divide plastics according to their colour or their ability to absorb light. The colour of sorted polymer streams can vary depending on the time of year, for example, more plant pots are likely to be recycled in summer.
Additionally, stringent standards require plastics intended for food contact to be separated from the rest. This separation is necessary as factors such as colour, smell, food contamination, and exposure to sunlight all impact the recyclability of a polymer.
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Material Recovery Facilities (MRF)
Plastic waste collected from homes, businesses, and recycling centres is sent to Material Recovery Facilities (MRFs) to be separated from non-plastic materials. MRFs are not drop-off facilities and do not accept materials for recycling. Instead, they are where recycling goes after it is picked up by a hauler.
MRFs use sorting equipment such as conveyor belts and optical sorters to separate plastic from non-plastic materials. Workers manually remove contaminants such as plastic film, wires, textiles, and organic materials. Cardboard and paper products are usually the first recyclables to be separated. Once the separating process is complete, there are six different collections of recyclables: cardboard and paper, steel, aluminium, glass, and plastic.
Each material is then sent to specific materials recycling facilities for further processing to become suitable for use in manufacturing. The objectives of MRFs are to increase the amount of recyclable material recovered, improve the reliability of waste management systems, reduce operational costs, and delay costly expansions of waste management facilities.
In addition to sorting plastic from non-plastic materials, some MRFs are equipped with advanced sorting machines that can separate different types of plastics. These machines use infrared, x-ray, or other cutting-edge sensors to recognise a polymer's unique signature and, in some cases, colour. This sorting process is important to maintain the integrity of the finished, recycled plastic.
The economic viability of recycling certain polymers depends on the local demand for those polymers. Therefore, sorting plastics before they are sold for recycling can be economically beneficial.
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Plastic Recovery Facilities (PRF)
The process begins with the collection of plastic waste from homes, businesses, and local recycling centres. The waste is then transported to a Material Recovery Facility (MRF), which separates plastic from non-plastic materials. The plastic is then sent to a PRF for further sorting into different types of plastic polymers. This step is crucial as different plastic polymers have distinct characteristics, and mixing them would alter these properties. Therefore, the outcome of each recycling process should be a single type of plastic polymer.
PRFs use advanced sorting equipment such as optical sorters, which can distinguish between various types of plastics. They may also use techniques like sink-float separators, where high-density plastics sink in water while low-density plastics float, and sorting machines that employ infrared, x-ray, or other advanced sensors to recognise a polymer's unique signature and colour.
The sorted plastic polymers are then baled and sold or sent to a pelletising facility, where they are processed into plastic pellets. These pellets are the final product, ready to be used in new plastic items.
Overall, PRFs play a vital role in ensuring the integrity and quality of recycled plastic by separating and preparing plastic waste for further processing, contributing to a more sustainable future.
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Wet processes
The recycling of plastic is a complex process that starts with the collection of plastic waste from homes, businesses, and local recycling centres. The plastic waste is then sent to Material Recovery Facilities (MRFs) that separate plastic from non-plastic materials. The next step is sorting the plastic waste into different types of plastic, which can be done manually or by using specialised equipment such as optical sorters or sink/float separators.
One of the important methods used to separate plastic materials is a wet process known as a Sink-float separator. In this process, a tank is filled with water, and the plastic waste is placed inside. The high-density plastic sinks, while the low-density plastic floats, allowing for separation. This process is also known as float-sink separation or hydrocyclone separation. The separated plastics are then recovered for further processing, which includes washing, shredding, and melting.
The washing process is crucial as it removes impurities such as product labels, adhesives, and food residue. It also helps dissolve any adhesives used to attach labels. After washing, the plastic is shredded into smaller pieces, which can be used as additives or sold as raw materials. Additionally, shredding helps remove metals and other impurities.
Following the shredding process, the plastic may undergo further sorting using optical sorting machines or sink-float separators to separate the plastic by thickness, colour, size, and type. This step ensures that any remaining contamination is removed before the plastic is processed further.
The final stage of the wet processes involves crushing and melting the sorted and cleaned plastic to form pallets called nurdles or pellets. These pellets are then sold to manufacturers to be used in new products.
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Frequently asked questions
Collectors from the government or private companies gather all post-consumer plastic waste from homes, businesses, schools, and other institutions.
The collected plastic waste is sent to a Material Recovery Facility (MRF) to separate plastic and non-plastic materials. This may involve manual picking, where large items, non-recyclables, and contaminants are removed by hand.
The plastic waste is then sent to a Plastic Recovery Facility (PRF) for further sorting into different types of plastic. This can be done using advanced sorting machines that employ technologies such as near-infrared technology (NIR), float tanks, optical sorting, or a newly developed camera technology that can distinguish between 12 different types of plastic.
Different plastic polymers have unique characteristics, and mixing them would alter these properties. Therefore, separating different polymers ensures that the recycled plastic maintains its integrity and is not downgraded to a lower grade, which may render it non-recyclable.
The sorted plastic is then washed, shredded, and further sorted. It is then melted and formed into new recycled plastic pellets, which can be sold and used to create new products.
