Ethan Clarke
Plastic is one of the most popular and useful materials of modern times, with 300 million tonnes produced worldwide each year. However, the plastic industry depends on non-renewable resources, and plastic production contributes significantly to global warming. While many commonly used plastics can be recycled, only about 10% of all the plastic ever produced has been recycled, with recycled plastic almost always being of lower quality than primary plastic. The process of recycling plastic involves collection, sorting, and reprocessing, but it is often disrupted by contamination from non-recyclable plastics or food residue. After being collected by local authorities or waste management contractors, plastic waste is sent to Material Recovery Facilities (MRFs) to be sorted by type. The sorted plastic is then washed, shredded, melted, and formed into pellets, which are sold to producers of recycled plastic products.
| Characteristics | Values |
|---|---|
| Plastic recycling rate in the US in 2018 | 8.7% |
| Plastic recycling rate in the US in 2021 | 5% |
| Amount of plastic waste that ends up in landfills | 49% |
| Amount of plastic waste that is mismanaged or littered in nature | 22% |
| Amount of plastic waste that is incinerated | 19% |
| Amount of plastic waste that enters the ocean yearly | 1-2 million tons |
| Amount of tap water in the US contaminated by plastic | 95% |
| Coca-Cola's plastic packaging production in 2017 | 3 million tons |
| Average amount of plastic consumed by a person weekly | 5 grams |
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What You'll Learn
Collection and transportation
The recycling process begins with the collection of plastic waste from homes, businesses, and local recycling centres. This is typically done through kerbside collection services, where local authorities or waste management contractors collect recycling from individual or communal bins on a weekly or bi-weekly schedule. This is the most common form of plastic packaging recycling collection. However, it is important to check local programs to confirm what specific materials are accepted for recycling in a particular area.
In some cases, haulers may use one truck to collect both recycling and trash. In these instances, the recyclables are kept separate from the trash within the truck, allowing them to be sorted and reprocessed into new materials later on.
Once collected, the plastic waste is transported to transfer stations, which act as central locations before the materials are moved on to recycling facilities. These facilities include Material Recovery Facilities (MRFs), which handle plastic and non-plastic materials, and Plastic Recovery Facilities (PRFs), which handle only plastic. MRFs sort through the recyclables and divide them into categories such as paper, metal, glass, and different types of plastic. The sorted plastics are then sent to reprocessors, where they undergo further processing.
The mode of transportation used in the supply chain can significantly impact the carbon footprint of the recycling process. Shipping by rail, for example, can lower logistics costs and reduce greenhouse gas emissions compared to shipping by truck. As the demand for recycled plastic resin rises, adopting more sustainable transportation methods will be crucial for companies to meet their sustainability targets.
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Sorting and cleaning
Sorting plastic for recycling can be a challenging process, akin to "conducting a symphony of innovation and expertise". It requires a combination of cutting-edge technology and human involvement to accurately identify, sort, and prepare plastic items for the next stages of recycling.
Sorting
The first step in the recycling process involves collecting plastic from homes, businesses, schools, and recycling centres. This plastic waste is then sent to Material Recovery Facilities (MRFs) that handle plastic and non-plastic materials, or Plastic Recovery Facilities (PRFs) that specifically sort plastic by type.
At these facilities, plastic items are sorted according to various characteristics, including resin or polymer type, density, colour, size, thickness, and shape. This sorting process is crucial to ensuring the quality and safety of the final recycled product, as different types of plastic have unique properties and recycling requirements.
To accomplish this, recycling facilities employ advanced sorting technologies, such as:
- Near-infrared (NIR) spectroscopy: This technique shines near-infrared light onto plastic items, and sensors analyse the reflected light to determine the resin or polymer type based on their unique molecular structures.
- Optical sorting machines: These machines use optical detection systems to separate plastics by colour.
- Sink/float separators: By using water tanks, this method separates plastics according to their density, with lighter plastics floating and heavier plastics sinking.
- Metal detectors and magnets: These help identify and remove metals from the plastic waste stream.
- X-ray and other cutting-edge sensors: These technologies can recognise a polymer's unique signature, including its ability to absorb light, and in some cases, its colour.
While automated systems have significantly improved sorting accuracy, skilled workers are still essential for dealing with irregularly shaped or unusually coloured plastic items, as well as identifying and separating non-recyclable plastics like PVC.
Cleaning
Once sorted, the plastic waste undergoes an extensive cleaning process to remove impurities, contaminants, and residual waste. This step is crucial as it ensures the purity and quality of the final recycled product. The cleaning methods include:
- Washing: Plastic is washed with hot or cold water, sometimes with the assistance of detergents, disinfectants, or other cleaning agents, to remove dirt, food scraps, adhesives, labels, and other residues.
- Dry-cleaning: Various dry-cleaning approaches are being investigated to reduce water consumption and costs associated with conventional wet cleaning. These include mechanical cleaning with compressed air, rotor disks, or fluidized sand beds.
- Melt filtration: This process involves melting the plastic and filtering out contaminants, although it is more commonly used in the reprocessing stage.
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Shredding and melting
Shredding is typically done through mechanical shredders, which use rotary cutters, guillotines, or swivelling hammers to cut or pulverize the plastic into industry-size requirements. This process produces plastic flakes, which are then washed to remove contaminants. The washed plastic flakes undergo further sorting to ensure a pure stream of material.
After shredding and sorting, the plastic is ready for the melting stage, also known as extrusion. It is heated and forced through an extruder, where it is cut into pellets or "nurdles". These pellets are sold to manufacturers, who use them to create new products. The melting point and extrusion process vary depending on the type of plastic. For example, PET and PVC plastics have a melting point above 200°C, making them suitable for dry-processed technologies, where they are incorporated into hot aggregates before adding asphalt binders. On the other hand, plastics with lower melting points, such as PS, PP, and LDPE, are more suitable for wet-processed technologies, where they are added directly to the asphalt binders before mixing with aggregates.
Overall, the shredding and melting steps in plastic recycling play a vital role in reducing plastic pollution, minimizing waste, and promoting the reuse and repurposing of plastic materials.
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Forming pellets
Plastic pellets are an essential part of the recycling process, playing a key role in creating new plastic products from recycled materials. They are commonly used in many industrial sectors, including packaging, automotive, electronics, agriculture, and construction. These pellets are made from recycled or virgin plastic raw materials and are processed into various products, such as bottles, bags, auto parts, and toys. The process of forming pellets involves several steps, and it begins with the preparation of raw materials.
Firstly, raw materials, which can include polymers, additives, and pigments, are mixed in precise proportions. This step is important as it ensures the desired characteristics of the final product, such as strength, durability, UV resistance, and fire resistance. The mixed raw materials are then fed into an extruder, which passes them through a high-temperature melting zone. This melting zone softens the polymers and blends them with the additives, creating a molten mixture.
The molten mixture is then pushed through a die, forming a continuous shape of molten plastic. This process is known as extrusion and is a crucial step in creating the desired shape for the pellets. After extrusion, the liquid material is filtered to eliminate any residues or impurities. This ensures that the final product is of high quality and meets the required standards.
Following the extrusion and filtering steps, the continuous form of molten plastic is rapidly cooled using a water cooling system or dry ice. This process solidifies the plastic, making it brittle and easier to cut into small pieces. The solid, brittle form is then cut into small cylindrical pieces called plastic pellets using a machine called a granulator or a cutter. The size of these pellets is similar to that of a lentil, making them easy to store and handle in various industrial operations.
Finally, the plastic pellets are stored in bags or containers for later use. It is important to store them in a dry, cool place, away from direct sunlight, to prevent any risk of moisture or degradation. These stored pellets then become the raw material for creating new plastic products, completing the cycle of plastic recycling and reducing the amount of plastic waste that ends up in landfills or oceans.
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Creating new products
Plastic recycling is critical to improving the environment and bettering waste management solutions. Recycling plastic can conserve limited natural resources and energy. As plastic is made from oil, recycling it reduces the need to make more plastic from raw materials, thereby conserving oil.
The process of recycling plastic to create new products involves several steps. Firstly, plastic is collected from homes, businesses, local recycling centres, and smaller recycling sites in communal areas such as supermarket car parks. The second stage is sorting the plastic from other materials, which is done at a Material Recovery Facility (MRF). The plastic may then be sent to a Plastic Recovery Facility (PRF) for further sorting into different types of plastic. Sorting is done automatically, with a manual sort to ensure all contaminants have been removed.
Once sorted, the plastic is washed, shredded into flakes, and melted down into pellets. These pellets are sold to manufacturers to be used in new products. The plastic can also be processed into a polymer that manufacturers can use to make new plastic products.
A wide range of products can be made from recycled plastic. For example, recycled PET plastic bottles can be transformed into flakes, which can be spun into yarn and used to manufacture clothes and other textile garments. Recycled PET can also be used to make new PET bottles, shampoo bottles, cosmetic caps, packaging films, polar fleece clothes, backpacks, and carpets. In addition, plastic bottles can be filled with sand, stacked, and cemented together to form a building's structure, a technique that is gaining momentum in third-world countries.
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Frequently asked questions
The plastic is collected and sent to a Material Recovery Facility (MRF) to be sorted. The plastic is then washed, shredded, and sorted further before being melted and formed into pellets. These pellets are then sold to be used in new products.
The three main steps involved in recycling plastic are collecting, sorting, and reprocessing.
Plastic is sorted by type, colour, thickness, and usage. Sorting is done manually or by machines at recycling plants.
Unfortunately, most plastic that is collected for recycling is not actually recycled. Some plastic is sent to landfills or is illegally dumped and open-burned. A small amount of plastic is recycled and turned into new products.
Plastic is not designed to be recycled. Recycling plastic is difficult because there are many different types of plastic, and they do not mix well when melted down. Also, the long polymer chains that make up plastic become shorter each time they are melted, resulting in lower-quality recycled material.
