Chloe Zhang
Plastic recycling plants are facilities that receive waste from citizens' homes and separate them into different streams of recyclables. The process of recycling plastic involves several organisations working together, from the public to manufacturers and designers. The plastic recycling process involves several steps, from sorting to washing, shredding, melting, and finally, forming new products. The more plastic that is recycled responsibly, the better it is for the planet.
| Characteristics | Values |
|---|---|
| Objective | To convert waste into resources that can be used to create new products |
| Waste Collection | The waste collection service of each municipality is responsible for collecting and transferring the contents of the containers to the recycling plant assigned to each municipality |
| Waste Sorting | Once at the plant, the contents are dumped onto a bulky waste sorting belt. Manual and mechanical sieving is carried out to separate the waste by fraction and discard any unwanted waste |
| Washing | Reprocessors wash the plastic |
| Shredding | Reprocessors shred the plastic |
| Extrusion | The plastic is melted down and forced through an extruder, then cut into pellets |
| Selling | Pellets are sold to manufacturers |
| Product Creation | Manufacturers incorporate the pellets into their products |
| Design | Designers, brands, and retailers play a role in the recycling system by designing products that can be recycled easily and effectively and can incorporate recycled plastic |
| Collection | Local authorities, waste management contractors, and independent waste collectors collect the recycling and transport it to transfer stations |
| Transfer Stations | Transfer stations act as a central location for the recycling to be collected before being moved to a recycling facility |
| Separation | Machines separate recyclables into the appropriate category. An OCC screen separates old corrugated cardboard from mixed recyclables. A ballistic separator moves rigid waste items to one end and flexible items to the other. A magnet separator removes any metal. An eddy current separator magnetizes aluminium and pushes it off the conveyor belt. |
| Weighing | Before material enters the facility, it is weighed to determine how much material is coming into the facility |
| Pre-Sort | Humans recognize and remove things that can damage equipment or injure people |
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What You'll Learn
Sorting plastic from other recyclables
At the recycling facility, the waste is weighed, and then unloaded onto a main feed conveyor belt. The first step in sorting recyclables is often a pre-sort, where humans identify and remove items that could damage equipment or pose safety hazards. This includes items like Christmas lights, machetes, hoses, cords, wires, metal hangers, plastic bags, and other "tanglers."
After the pre-sort, the waste undergoes various mechanical sorting processes. One common method is the use of a star screen, which consists of quickly spinning discs that separate flat, lightweight materials like paper and cardboard from heavier materials. Another method is a ballistic separator, which uses oscillating paddles to separate rigid items (such as bottles, containers, or cans) from flexible items (such as paper, card, newspapers, and plastic wrapping).
For separating different types of plastics from each other and from other materials, more advanced technology is used. Some plants employ workers to manually check each item and sort it by number, while newer plants use infrared sensors that can identify the type of plastic based on light reflection. An air classifier is another machine used to separate lighter items from heavier ones, with plastic and aluminium being pushed up and out of the machine, while heavier glass falls to another conveyor belt.
Additionally, a magnet separator is used to remove metals, and an eddy current separator is used specifically for separating aluminium from other materials. It creates an induction field that magnetises aluminium, causing it to be pushed away from the conveyor belt as it passes over a magnetic rotor.
Finally, it is important to note that not all plastics are worth recycling. For example, Styrofoam could be melted down, but it changes the structure, making it uneconomical. PVC needs to be converted into a powder at specialty plants to prevent the release of toxins during melting. These considerations play a crucial role in sorting plastic from other recyclables and ensuring that the recycling process is effective and environmentally beneficial.
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Sorting different types of plastic
Sorting plastic effectively requires knowledge of these different types and their unique characteristics. Some plants employ workers to manually check each item and sort it by number, while newer plants utilise infrared sensors that use light to determine the type of plastic and sort them accordingly. This technology, known as optical sorters, acts like a giant eye, shining an infrared light on objects, with the reflected light signalling to a computer the type of plastic scanned.
After the initial sort, the plastic waste undergoes further separation from other materials. For example, a density separator removes glass by vibrating it through fine metal screens and knocking it out with puffs of air. Similarly, ferrous metals, those containing iron, are removed with a giant rolling magnet. This leaves materials like plastic and aluminium on the conveyor belt.
To separate these remaining materials, they are moved into an eddy current separator, which is a drum that creates an induction field to magnetise aluminium, allowing it to be separated from plastic. This is because, unlike steel and tin, aluminium is separated using this specific technology.
Finally, the sorted plastic waste is processed. It is washed, shredded, melted, and formed into pellets or "nurdles". These pellets are then sold to manufacturers who incorporate the recycled plastic into new products.
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Washing, shredding and extruding plastic
The process of plastic recycling involves several steps, with plastic waste being collected, sorted, cleaned, shredded, and then reprocessed through extrusion.
Washing
The first step in the recycling process is the collection of plastic waste from homes, businesses, and schools. This is typically done by local authorities or waste management contractors. The plastic waste is then taken to Material Recovery Facilities (MRF) or Plastic Recovery Facilities (PRF) to be sorted and washed. The washing process ensures that any dirt, food residue, chemicals, or other contaminants are removed from the plastic. This step is crucial as contamination can disrupt the recycling process and send plastics to landfills instead of being recycled.
Shredding
After being washed, the plastic is sent through shredding machines to be ground into smaller, uniformly-sized pieces. This is done to increase the surface area of the plastic, making it easier to clean and process in the next steps. There are different types of shredders, such as single-shaft and four-shaft shredders, that use various methods like rotary cutters or guillotines to cut the plastic to the required size.
Extruding
The shredded plastic then undergoes the extrusion process, where it is melted down and forced through an extruder. As the plastic comes out of the extruder, it is cut into pellets, which are then sold to manufacturers. These pellets can be used to create new plastic products such as trash cans, buckets, or containers. The extrusion process allows the recycled plastic to be reprocessed and moulded into new shapes, such as bottles or clothing.
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Melting plastic into pallets
Plastic recycling is a vital process in managing waste and creating a more sustainable future. The process of melting plastic into pallets involves several steps, and the specific process can vary depending on the type of plastic being recycled.
Firstly, it is important to separate different types of plastics, as they have different properties and require different treatments. Some plants use workers to manually check and sort each item, while newer plants employ infrared sensors that use light to determine the type of plastic. Certain types of plastic, such as Styrofoam and PVC, are not worth recycling due to the changes in their structure when melted or the toxins released.
After sorting, the plastic waste is washed and shredded to facilitate the melting process. This is a crucial step in preparing the plastic for the next stage of extrusion. During extrusion, the shredded plastic is melted and forced through an extruder, where it is cut into small pellets. These pellets are then sold to manufacturers.
The plastic pellets can now be melted and moulded into pallets. One method is structural foam moulding, which is less expensive and uses gas to create porous pallets with high weight capacity. Thermoforming is another process where sheet plastic is heated and pulled into a mould using a vacuum. This method produces pliable pallets that can withstand fork tine abuse but cannot handle heavy weights. Other less common processes include blow moulding, rotational moulding, and compression moulding, which are typically used for low-volume production.
The choice of process and type of plastic depends on the specific business needs, such as weight capacity, durability, and cost. Recycled plastic pallets offer a more sustainable alternative to traditional wood pallets, with advantages such as durability and impact resistance.
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Creating new products from recycled plastic
Recycling plants are facilities that receive waste from citizens' homes and separate them into different streams of recyclables. The objective of these plants is to convert waste into resources that can be used to create new products.
The creation of new products from recycled plastic begins with the collection of plastic waste. Local authorities and independent waste collectors gather plastic waste from households and transfer stations, which then gets transported to recycling facilities. At the recycling facility, the plastic waste undergoes various sorting processes, with some plants employing workers to manually sort the plastic by type, while newer plants use infrared sensors that utilise light to determine the type of plastic.
After sorting, the plastic waste is washed, shredded, and melted down (extruded) by reprocessors. This molten plastic is then forced through an extruder and cut into small pellets, also known as nurdles. These pellets are sold to manufacturers who incorporate them into their products. The recycled plastic can be used to create a wide range of new products, such as clothing, carpet fibres, water bottles, and soda bottles.
The specific type of plastic determines its end use. For example, Polyethylene Terephthalate (#1 PET) is used for food and drinks due to its ability to block oxygen and carbon dioxide exchange, while High-Density Polyethylene (#2 HDPE) is used for creating stronger products like shampoo bottles and skin cream bottles due to its polymer chains.
The process of creating new products from recycled plastic not only helps to reduce waste but also supports a circular economy, minimising the environmental, health, and economic impacts of plastic pollution.
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Frequently asked questions
A plastic recycling plant is a facility that receives waste generated by citizens and deposited in containers in the city. Their objective is to convert plastic into resources that can be used to create new products.
Once the contents of the lorries are dumped onto a bulky waste sorting belt, the first review of the waste is carried out. Manual and mechanical sieving is then carried out to separate the waste by fraction and discard any unwanted waste. Some plants use workers to check each item and sort it by number, while newer plants have infrared sensors that use light to determine the type of plastic.
After sorting, the plastic is washed, shredded and extruded (melted down and forced through an extruder). The plastic is then cut as it comes out of the extruder to form pellets, which are sold to manufacturers.
Manufacturers purchase the pellets and incorporate them into their products. Designers, brands and retailers also play a role in the recycling system by designing products so they can be recycled easily and effectively, and can incorporate recycled plastic.
Plastics come in several types depending on the resin used to create the item. For example, #1 (PET) is used for food and drinks as it blocks oxygen from getting in and carbon dioxide from escaping, while #2 (HDPE) is used to make shampoo bottles as it creates a stronger product.
