Maya Ellison
Plastic recycling is an important part of preserving the environment and reducing our carbon footprint. However, sorting plastic for recycling can be challenging due to the hundreds of varieties of plastic, each with unique characteristics. To ensure the recycling process is efficient and successful, different types of plastic must be separated and placed in their own bins. This process involves using advanced technology, such as automated sorting systems with sensors and optical scanners, as well as human intervention for irregularly shaped or unusually coloured items. The sorted plastic then undergoes further stages of recycling, including resizing and compounding, to give it a second life as high-quality, reusable materials.
How to divide out plastics for recycling
| Characteristics | Values |
|---|---|
| Location | The recycling process differs based on location. For example, in some areas, all recycling is placed in one bin, while in other areas, different materials must be separated into different bins. |
| Separation by material type | Plastic should be separated from other materials such as aluminum, glass, and paper. |
| Separation by plastic type | Different types of plastics should be separated. This can be done using resin numbers, flotation, or advanced sorting machines that use infrared, x-ray, or other sensors. |
| Separation by physical characteristics | Plastic can be separated by size, shape, thickness, melting point, and colour. |
| Separation by recyclability | Non-recyclable plastics, such as PVC, should be separated from recyclable plastics. |
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What You'll Learn
Identify plastic type
Identifying the type of plastic is a critical step in recycling. It is important to note that the recycling symbol found on plastic products does not indicate that a product is necessarily recyclable or has been recycled. The number inside the chasing arrows triangle is a resin identification code that tells you what kind of plastic the material is made of.
Plastics with the number #1 or the letters PET or PETE are made from polyethylene terephthalate, one of the most commonly recycled plastics in the world. It is often used for water bottles, shampoo bottles, and yogurt containers.
Plastics with the number #2 or the letters HDPE are made from high-density polyethylene, which is one of the easiest plastic polymers to recycle and is accepted worldwide. HDPE is the stiff plastic used for milk jugs, detergent and oil bottles, toys, and some plastic bags.
Plastics with the number #3 are made from polyvinyl chloride (PVC) and are not considered recyclable. PVC is a soft, flexible plastic often used for bread bags, frozen food bags, and plastic shopping bags.
Plastics with the number #5 are made from polypropylene (PP) and are not accepted by most public recycling centers. PP is commonly found in medicine bottles, straws, and yogurt containers.
Other types of plastics include LDPE (low-density polyethylene), PS (polystyrene), HIPS (high-impact polystyrene), and ABS (acrylonitrile butadiene styrene). LDPE is considered less toxic and relatively safe but is not commonly recycled. PS, HIPS, and ABS are not mentioned as commonly recycled plastics, so it is best to check with local recycling programs to confirm if these types of plastics are accepted.
In some cases, plastic items may not have any resin numbers or symbols. Two simple methods can help identify the type of plastic: the floatation test and the heat test. The floatation test involves using a brine solution (salt) to separate heavier plastics that sink from lighter plastics that float. The heat test involves applying heat to separate plastics by their melting point.
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Separate by density
Density separation is a crucial step in the recycling process, allowing plastics of different densities to be separated and sorted for further processing. This method is particularly useful for separating plastics from other materials such as wood and metal, as well as separating different types of plastics.
The "float/sink" method, also known as sink-float technology, is a simple and cost-effective way to separate plastics by density. This method was borrowed from the mining industry in the 1970s and has been used successfully by plastics recyclers ever since. In this process, plastics are placed in water or a brine solution, with denser plastics sinking and lighter plastics floating to the top. This method is simple, inexpensive, and highly effective, as it does not depend on the size, shape, or composition of the materials being separated.
Another method for density separation is the use of cyclones, such as the LARCODEMS (Large Coal Dense Medium Separator) technology. Cyclones use centrifugal force to separate materials by density, with denser materials moving towards the outside and lighter materials towards the centre. This method has been shown to effectively process a wide range of particle sizes, from 0.5 up to 120 mm, achieving high purities and recoveries for both high-density and low-density products.
At an industrial scale, advanced sorting machines can also be used to separate plastics by density. These machines use infrared, x-ray, or other cutting-edge sensors to identify and separate plastics based on their unique signatures, including their density. This technology can handle large volumes of plastics and is highly accurate, ensuring the purity and quality of the final recycled products.
Overall, density separation plays a critical role in the recycling process, allowing for the efficient sorting and processing of different types of plastics and other materials. By using methods such as float/sink, cyclones, and advanced sorting machines, plastics can be effectively separated by density, contributing to a more sustainable and environmentally friendly world.
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Sort by colour
Sorting plastic by colour is an important step in the recycling process. It is often done after the initial separation of plastic from other materials like aluminium, glass, and paper, and after the separation of different types of plastics. Sorting by colour is usually done through automated systems, but there are instances where manual intervention is necessary, such as with irregularly shaped or unusually coloured plastics.
In the modern era of recycling, technology plays a crucial role. Automated sorting systems are equipped with sensors and optical scanners that identify and categorise plastic items based on attributes like density, colour, and behaviour when exposed to specific wavelengths of light. One of the groundbreaking technologies used in this process is near-infrared spectroscopy (NIR), which involves shining near-infrared light onto the plastic items. Different types of plastic absorb and reflect this light uniquely due to their varying molecular structures, allowing sensors to determine the resin type of each plastic by analysing the reflected light.
Optical colour sorting machines can effectively separate plastic by colour. These machines use fluorescent or ultraviolet light to divide plastics according to their colour or ability to absorb light. Near-infrared systems are also used to sort polymer types, relying on the different reflectivity of polymers to distinguish between their individual wavelength signatures. Optical detection systems further along in the process allow for colours to be separated.
The importance of sorting plastics by colour cannot be overstated. It helps to eliminate cross-contamination of polymers, ensuring that batches are suitable for reprocessing. Additionally, it contributes to the overall goal of creating a more sustainable and greener world by ensuring that plastics are properly recycled and reused.
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Divide by size and shape
Dividing plastics for recycling is an important step in preserving the environment and reducing our carbon footprint. While recycling protocols may vary depending on the area, it is generally recommended to separate plastics by size and shape, among other features, before placing them in their respective bins for proper disposal.
Size and shape are critical factors in the recycling process. Large plastic items, such as containers or packaging, may need to be crushed or shredded into smaller particles to facilitate efficient processing. This size reduction step not only helps in standardising the dimensions but also increases the surface area, making it easier for subsequent treatment processes.
The separation of plastics by size and shape can be achieved through various methods. One common technique is the use of floatation, where heavier plastics are submerged in a brine solution, allowing lighter plastics to float to the top. This process effectively separates plastics based on their density and buoyancy, ensuring that similarly-sized items can be grouped together.
In addition to floatation, advanced sorting machines and optical scanners play a pivotal role in dividing plastics by size and shape. These machines employ cutting-edge technologies, such as infrared, X-ray, and other sensors, to identify distinct attributes. They can analyse factors like density, thickness, and colour, ensuring accurate separation of plastics that have similar shapes and sizes but differ in other physical characteristics.
The importance of dividing plastics by size and shape cannot be overstated. It not only streamlines the recycling process but also helps eliminate cross-contamination of polymers. By separating plastics into distinct categories, recycling facilities can process each type effectively, reducing the risk of incompatible materials interfering with the recycling journey and rendering batches unsuitable for reprocessing.
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Place in separate bins
Placing different types of plastics in separate bins is an important step in the recycling process. This is because different types of plastics have distinct characteristics and processing requirements. Sorting plastics correctly is critical to recycling, as combining certain types of plastics can create dangerous chemical reactions, producing harmful dioxin emissions that can pose a risk to human health.
In some areas, local authorities may provide separate bins for different types of recyclables, including plastics. For example, some areas provide a yellow bin for cardboard and paper waste and a blue bin for plastic, glass, and cans. However, in other areas, all recyclables may be placed in a single bin for collection. It is important to check the local guidelines for your area to ensure that you are separating your plastics correctly.
When placing plastics in separate bins, it is important to identify the different types of plastics. Plastics are typically divided into six specific categories, each with its own resin type and unique characteristics. The most commonly recycled plastics include PET (polyethylene terephthalate), HDPE (high-density polyethylene), PP (polypropylene), and PVC (polyvinyl chloride). PVC, in particular, is difficult to recycle due to its chemical composition, so it is important to separate it from other plastics.
Automated sorting systems play a crucial role in separating plastics. These systems use advanced technology, such as optical scanners, infrared sensors, and x-rays, to identify and sort plastic items based on attributes like density, colour, and behaviour when exposed to certain conditions. Once the sensors identify a specific type of plastic, pneumatic systems use air jets to divert the plastic items into their respective collection bins, ensuring an efficient and streamlined sorting process.
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Frequently asked questions
Different types of plastics have different resin types, with their own unique characteristics, and each needs to be processed separately. When combined, certain types of plastics can create dangerous chemical reactions, producing harmful dioxin emissions.
Plastics can be identified by their resin numbers. If there are no resin numbers listed, you can use floatation to identify them. Bury heavier plastics in a brine solution (salt) and float lighter plastics to the top.
Recycling plants use automated sorting systems with an array of sensors and optical scanners to identify and separate plastics based on factors like density, colour, and resin type. Some plants also use manual labour to sort plastics.
It depends on the area you live in. Generally, areas with trash pickup will have you put all the recycling in one bin. More rural areas where you take your trash to the dump yourself will require you to sort it out.
