Maya Ellison
Sorting plastic for recycling is a crucial step in the recycling process. Different types of plastic have distinct properties, and separating them is essential to ensure the quality and safety of the final recycled product. This process can be challenging due to the various forms of plastic packaging and the presence of multiple layers, which can be difficult to separate. However, accurate sorting increases the value of recycled plastic and plays a vital role in reducing carbon emissions and protecting the environment. The sorting process involves identifying and categorizing plastic items based on their unique characteristics, such as resin type, colour, size, thickness, and density, using a combination of manual and automated systems.
Characteristics of Sorting Plastic for Recycling
| Characteristics | Values |
|---|---|
| Importance | Sorting plastics is important to increase their value, ensure worker safety, and improve the quality and safety of the final product. |
| Methods | Manual, automated systems, pneumatic systems, infrared technology, fluorescent markers, near-infrared, chemical recycling |
| Considerations | Resin type, cross-contamination, packaging design, colour, size, thickness, purity, safety, quality, cost, time |
| Plastics to Separate | PET, PVC, PS, PE, PP, HDPE, LDPE, LLDPE, HDPE, foreign polymers, paper, residue |
What You'll Learn
Sorting plastic by type
One of the initial steps in sorting plastic is separating plastic waste from regular waste. This is often done by collecting plastic waste in designated plastic bags, which are then transported to sorting facilities. At these facilities, the bags are opened, and the extensive sorting process begins.
Automated sorting systems play a significant role in identifying and categorizing plastic items. These systems use advanced technology, including sensors, optical scanners, and infrared detection, to analyze factors such as density, colour, and behaviour when exposed to specific wavelengths of light. This equipment can identify different types of plastic, such as PET and PVC, and divert them into specific collection areas using pneumatic systems and air jets.
However, there are instances where manual intervention is still necessary. Skilled workers are crucial for sorting irregularly shaped or unusually coloured plastic items that may pose a challenge for automated sensors. Additionally, they ensure that non-recyclable plastics, such as PVC, are identified and separated. PVC, commonly used in pipes and packaging, is challenging to recycle due to its chemical composition.
To further enhance the sorting process, separate collection schemes for different types of plastic can be implemented. This approach improves sorting output and helps achieve high-quality sorting standards, maximizing recycling volumes. It is also important to remove impurities, such as metals, labels, glue, dirt, and food scraps, through an extensive washing process before the plastic is processed into recycled products.
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Sorting plastic by colour
There are five types of general plastics: polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and acrylonitrile-butadiene-styrene copolymer (ABS). Each type of plastic has a distinct mix of dyes and additives that affect its colour, shape, structure, toughness, adaptability, and melting point.
To further assist in the sorting process, regulatory agencies and consumers are demanding products that are designed with the future health of the planet in mind. Colour variations and technology support the movement towards a reduce-reuse-and-recycle generation. The processes used to create these variations must be consistent from manufacturing to recycling. Spectrophotometers, for example, can be used to obtain accurate colour measurements and accommodate most colour measurement applications. This technology helps to decrease variables from various light sources and textures, providing consistent results and comparisons.
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Sorting plastic by size
Shredders and granulators with industrial blades perform rotational cutting to break down plastic into smaller particles. This increases the surface area of the plastic, making it easier to process. The operators of these machines are trained to identify and remove any non-plastic waste. Metal detectors are also used to ensure that only plastic waste is being processed.
After size reduction, the plastic pieces can be washed to remove traces of dirt and other contaminants such as paper, glue, sand, and grit. This step also helps to separate mixed plastic types, as they can be sorted based on density using float tanks.
In addition to size, plastic can also be sorted by other features such as shape, thickness, melting point, and colour. Infrared technology is commonly used to distinguish between different types of plastic, while optical colour sorting machines can separate plastic by colour.
Overall, sorting plastic by size and other characteristics is a crucial step in the recycling process, ensuring the purity and quality of the final recycled product.
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Sorting plastic by thickness
There are a few methods that can be used to sort plastic by thickness. One common method is to use automated sorting systems equipped with sensors and optical scanners. These systems can identify and sort plastic items based on various attributes, including thickness, density, and colour. The plastic waste is placed on a conveyor belt and moved through an array of sensors that analyse these factors. Once the sensors identify a specific type of plastic, pneumatic systems use air jets to divert the plastic items into different collection bins. This method is efficient and accurate, but manual intervention may still be necessary for irregularly shaped or unusually coloured plastic items.
Another method for sorting plastic by thickness is to use infrared technology, specifically near-infrared (750-2500 nm) systems. These systems use the different reflectivity of polymers to distinguish between their individual wavelength signatures and separate them accordingly. This technology can also be used in conjunction with fluorescent markers, which provide a unique signal to sorting equipment and help identify different types of plastic, including black plastics that are usually invisible to infrared systems.
In some cases, a combination of methods may be used to sort plastic by thickness. For example, infrared technology can be used alongside manual sorting by skilled workers to ensure the correct sorting decisions are made. Additionally, the plastic may be shredded first, and then further sorted by thickness, colour, or other characteristics.
Overall, sorting plastic by thickness is a crucial step in the recycling process, and a variety of methods and technologies are employed to ensure accurate and efficient sorting.
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Sorting plastic by resin type
The best way to recycle industrial amounts of plastic is to provide your recycling company with data sheets containing technical specifications for the plastic materials of each item you are trying to recycle. These specifications include the Melt Flow, Resin Number, Extrusion or Injection Grade, Izod, and Durometer for that particular type of plastic.
There are also tests to identify the type of plastic when no resin number is included on the item. For example, if the plastic drips and produces a burnt sugar smell, it is probably PET. If it does not catch fire at low temperatures and produces a blue-green flame, it is likely PVC. If it does not drip and produces black sooty smoke, it is probably PS.
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Frequently asked questions
Different plastics have different properties, and sorting them correctly is important for ensuring the quality and safety of the new recycled plastic. For example, shampoo bottles should be kept separate from drink cartons. Sorting plastic to a high degree of purity also means polymers can be reused and retain their value.
Sorting plastic at scale is typically done using automated systems equipped with sensors and optical scanners. These sensors can analyse factors like density, colour, and the plastic's behaviour when exposed to specific wavelengths of light. Once the sensors identify a specific type of plastic, pneumatic systems use air jets to divert the plastic items into different collection bins.
Plastic waste is often separated in households using plastic bags. You can separate plastic waste into different bags or bins based on the type of plastic. Common types of plastic to separate from each other include PET (e.g. drink bottles), PVC (e.g. pipes and packaging), and PS (e.g. disposable cutlery and foam packaging).
