Omar Khalid
Sorting plastic from trash is an important step in the recycling process. Plastics are typically sorted by consumers into different streams of plastic waste, which is then transported to sorting installations for further separation. This separation is important for ensuring the quality and safety of the new recycled plastic. Sorting plastics can also increase their value and prevent dangerous chemical reactions that may occur when certain plastics are mixed together. To identify different types of plastics, recycling companies use advanced technologies such as near-infrared spectroscopy and optical scanners, as well as manual inspections by skilled workers.
| Characteristics | Values |
|---|---|
| Sorting | Done by households, companies, and at sorting installations |
| Sorting installations use infrared technology and other advanced technologies to identify and separate different types of plastics | |
| Sorting to a high degree of purity means polymers can be reused and retain their value | |
| The end goal is a 100% pure plastic product | |
| Sorting is essential for safety reasons as some plastics can cause dangerous chemical reactions when mixed | |
| Sorting is also important to ensure the quality of the final product | |
| Sorting is done manually and through automated systems | |
| Collection | Plastic waste is collected from households and companies and transported to local factories with big separation machines |
| In 2018, 360 million tonnes of plastic were produced globally, with 62 million tonnes produced in the EU and only 9.4 million tonnes collected for recycling in its member states | |
| Washing | Before being processed into granulate, plastic waste undergoes an extensive washing process |
| Shredding | Plastic waste is shredded and granulated in an extruder |
| Melting | Plastic is melted down into new products |
| Excess plastic is converted into electricity and district heating |
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What You'll Learn
Sorting plastic by resin type
There are several methods to identify the resin type of a plastic item. Many plastic items will include a resin identification code, which is part of the "Voluntary Plastic Container Coding System" first introduced by the US Society of the Plastics Industry (SPI) in 1988. The system has been adopted by a growing number of communities implementing recycling programs, as a tool to assist in sorting plastics. The different resin identification codes are part of the Unicode block called Miscellaneous Symbols and have the following codes: ♳ (U+2673), ♴ (U+2674), ♵ (U+2675), ♶ (U+2676), ♷ (U+2677), ♸ (U+2678), ♹ (U+2679), and ♺ (U+267A).
In some cases, a plastic item may not have a resin number included. In these cases, there are other methods to determine the resin type. One approach is to perform a burn test. For example, if the plastic drips and produces a burnt sugar smell, it is likely PET. If it does not catch fire at low temperatures and produces a blue/green flame, it is probably PVC. If it does not drip and produces black sooty smoke, it is likely PS.
Another technology for identifying resin types is the Tribopen from Peter Walker Systems of Bergheim, Germany. The Tribopen is a pen with a piston-type sensor head that generates an electrostatic charge when rubbed on the plastic. Each material generates a different charge, and LEDs on the pen indicate the polymer type. However, it cannot distinguish between closely related members of the same resin family, such as LDPE and HDPE.
Automated systems have also been developed to sort plastic by resin type at high speeds. For example, TiTech Autosort of Oslo, Norway, has created an automated near-infrared scanning system that sorts bottles by polymer type at rates of up to 8,800 lb/hr. The system uses a conveyor belt, with good bottles dropping off onto a second conveyor and reject bottles blown upwards by an air jet.
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The importance of purity in recycled plastic
Plastic is a significant contributor to environmental degradation, with substantial quantities of discarded plastic accumulating as debris in landfills and natural habitats worldwide. Recycling is thus essential to reducing plastic waste and its environmental impact. However, the plastic recycling process is complex and intricate, requiring careful sorting, washing, shredding, and granulating.
The purity of recycled plastic is of utmost importance in the recycling industry. High-purity recycled plastic retains its value and can be reused to create new, high-quality products. The purity of the plastic feed determines its suitability for different applications. For example, recycled PET plastic is in high demand for producing drink bottles, but only high-purity rPET meets the requirements, making effective sorting crucial.
Sorting plastic is essential for safety and quality reasons. Different types of plastic have distinct properties, and mixing certain plastics can lead to dangerous chemical reactions. For instance, adding a single PVC container to 900 lbs of PET bottles can contaminate the entire batch, producing harmful acids or toxic dioxin emissions.
Furthermore, sorting plastic into separate streams is critical for successful recycling. The variety of plastic types and packaging designs, such as multi-layer packaging, can complicate the sorting process and reduce the recyclability of the material. Effective sorting ensures that polymers can be reused and retain their value, contributing to a more sustainable and profitable recycling process.
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Using technology to identify plastic types
Plastic identification methods are essential for recycling, waste management, and manufacturing. These methods enable the sorting and separation of different plastics, increasing the efficiency of the recycling process and reducing contamination. The development of new technologies and techniques is crucial to address the ever-growing plastic waste problem.
One of the earliest plastic identification methods was introduced in the 1970s by the Society of the Plastics Industry (SPI). The SPI developed the Resin Identification Code (RIC), which identifies the type of plastic resin used in a product. The RIC code consists of a number within a triangle, ranging from Polyethylene Terephthalate (PETE) to Polystyrene (PS). However, the RIC code has limitations as it does not provide information on additives or other factors affecting recyclability.
Advancements in technology have led to the use of artificial intelligence (AI) and machine learning for plastic identification. These technologies can analyse large datasets and provide accurate, real-time identification results, making sorting more efficient. AI can identify various plastic types, including those that float and sink, such as polyolefins, which typically float, and nylon, which sinks.
Additionally, the development of biodegradable plastics is gaining interest. Biodegradable plastics break down naturally, reducing environmental impact. However, they also have drawbacks, such as the slower degradation process in domestic composters, which can emit methane gas.
The identification of plastic types is a critical step in the recycling process, and the use of technology in this area will continue to evolve to meet the challenges posed by plastic waste.
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How to identify PVC
One way to identify PVC is by its appearance. PVC is usually soft, tough, and sticky, with a yellowish, translucent, and glossy look. It is more flexible than low-density polyethylene but less so than polypropylene. Bending marks are often present.
Another method is to test the density of the plastic. Polyethylenes and polypropylenes float in water (density = 1 g/mL), while most other plastics sink. PVC is denser than water and will not float in glycerin (density = 1.26 g/mL).
The Beilstein copper wire test can also indicate the presence of chlorine, which is found in PVC.
The float test and burn test are other methods that can be used to rule out certain plastics, although they may not specifically identify PVC.
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The role of humans in the sorting process
Sorting plastic from trash is an important step in the recycling process. While technology plays a significant role in sorting plastics, human involvement is also crucial. The role of humans in the sorting process is multifaceted and ensures the accuracy and efficiency of the overall operation.
One of the primary roles of humans in plastic sorting is to perform manual sorting when automated systems encounter challenges. For instance, irregularly shaped or unusually coloured plastic items can confuse automated sensors. In such cases, skilled workers intervene to ensure correct sorting decisions are made. They identify and separate non-recyclable plastics, such as PVC, which is challenging to recycle due to its chemical composition. Human expertise is vital in these situations to maintain the accuracy and harmony of the recycling process.
Additionally, humans are responsible for conducting quality inspections throughout the sorting process. While automated systems provide initial sorting, humans draw samples of granulate produced from sorted plastic to test for homogeneity and quality. They detect and correct deviations, such as colour inconsistencies, to ensure the final product meets the required standards. This human-led quality control is an integral part of maintaining the safety and market value of recycled plastic.
In some cases, humans also play a role in sorting plastic waste at the household level. This involves separating different types of plastics into designated containers to facilitate proper recycling. This initial human-led sorting step is essential as it reduces the complexity of downstream sorting processes.
Furthermore, humans are key in developing and implementing innovative solutions for the plastic recycling process. With increasing demands for recycled content in products, humans work on creating accurate and efficient sorting technologies. For example, the Prism project in the UK has developed fluorescent markers that provide unique signals to sorting equipment, aiding in the recovery of food-grade polymers. Human ingenuity in this context helps improve the overall recycling rates and the environmental impact of plastic waste.
In conclusion, the role of humans in the plastic sorting process is vital. From manual sorting interventions to quality inspections and household sorting, human involvement ensures accuracy, safety, and efficiency in plastic recycling. Additionally, human ingenuity drives the development of innovative solutions, improving recycling rates and enhancing the circular economy of plastics.
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Frequently asked questions
Sorting plastic out of trash is crucial because it allows for the plastic to be reused and retain its value. Plastic is made from oil, and it takes a lot of energy to produce new plastic. By recycling one kilo of plastic, the environment is saved one and a half kilos of CO2.
Recycling companies use advanced technologies to sort plastic. One such technology is near-infrared spectroscopy (NIR), which involves shining near-infrared light onto plastic items. Different types of plastic absorb and reflect this light uniquely due to their varying molecular structures. Sensors analyse the reflected light to determine the resin type of each plastic. Other factors used to sort plastic include density, colour, and the plastic's behaviour when exposed to specific wavelengths of light.
At-home plastic sorting typically involves separating plastic waste into different bags or containers. It is important to identify non-recyclable plastics, such as PVC, and ensure they are kept separate from recyclable plastics. You can also check for resin numbers on plastic items to help identify the type of plastic. Additionally, some mobile phone apps can scan packaging and help identify if it is recyclable.
Different types of plastics have distinct mixes of dyes and additives, which affect their colour, shape, structure, toughness, adaptability, and melting point. Sorting plastics separately is essential to ensure the quality and safety of the new recycled plastic. For example, mixing certain types of plastics can cause dangerous chemical reactions. Sorting plastics into categories like soft plastics, hard plastics, and drink cartons is crucial for creating pure and valuable recycled plastic products.
