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Reusing fabricated plastic materials to make them available for further industrial processing can result in cost savings, reduced energy consumption, and lower environmental impact. Reclaimed plastic can be used to manufacture products such as packaging, plastic lumber, furniture, and a range of composite materials. Polyethylene terephthalate (PET) is one of the most commonly recycled polymer resins, and it is used for manufacturing synthetic fibers and plastic containers, including bottles. Over a million tons of PET materials are reclaimed each year and resold to manufacturers worldwide.
Plastic recycling and reclamation services employ a number of different techniques to convert post-consumer resin into workable stock. A range of variables, such as transparency or coloring, influence the methods and intended applications for recycled PET products. The quality and yield of the plastic are also important criteria, as is the amount of peripheral material attached to the base resin. The challenge of separating non-reusable elements from the reclaimable plastic portions can alter the cost-efficiency and effectiveness of a reclamation project.
Sorting and Granulation
Before reclamation begins, used PET products are crushed into bales and sold to a material recovery company. The first stage in a typical PET plastic reclamation procedure involves sorting the different types of resin in order to group them together. After they have been sorted, the plastic products are ground into particles whose size depends on the particular processing method that will be used on them. These resin granules are referred to as “flakes,” and will serve as the base forming material for future products.
Maintaining the purity of the flakes is important for preserving the reclaimed plastic’s value, as non-reusable elements can reduce workability and, ultimately, profitability. After grinding, air classification methods can be applied to filter out lighter materials, such as labels or caps, from the reclaimable plastic base. The granulation process itself helps to separate non-resin materials from the stock, but adhesives and attachments can impede the process, subsequently raising the cost of flake production by lowering total yield.
Granulated resin usually needs to be washed before it can move on to the next stage of processing. This washing can be conducted at standard environmental temperatures or at elevated heat levels. Disinfectants and detergents are often used to provide additional cleanliness. Once again, peripheral material, such as ink, linings, inserts, glue, and coatings can interfere with washing and result in a contaminated batch of resin. Ink can sometimes seep into the washing water and cause streaking, while glue remnants can cause other contaminants, such as label fragments, to adhere to the washed resin. To reduce the risk of compromised stock, recycled plastic often undergoes a second round of air classification after the washing cycle in order to remove unwanted material.
Plastic base resin and un-reusable materials usually have different density levels, allowing them to be separated through a hydrocyclone apparatus or a water bath. When using water, heavier resin will sink to the bottom, while lighter contaminants float to the surface. However, separating different resins from one another can be difficult, especially if they have similar density ratings. For example, a product composed of PET and PVC materials may be challenging to break down because these two materials tend to have close or overlapping densities. Products that have attachments formed from the same base resin or from a material with a significantly divergent density are therefore easier to process.
Drying and Filtering
After the grinding, washing, and separation are complete, reclaimed plastic is rinsed off to eliminate any remaining dirt or accumulated disinfectants from earlier stages in the process. The plastic can then be dried to prepare it for reintroduction as a manufacturing material or to undergo further treatment. Melt filtering is a fairly common post-reclamation treatment that is performed at a converter station. This filtration technique is intended to further purify the stock by removing any non-melting contaminants that may have lingered through the granulation, cleaning, and separation procedures. It uses an extruder that melts the plastic flakes and passes them through a series of screens that form the material into pellets, while blocking any non-melted particulate. Pelletizing the plastic improves the uniform quality of the stock, making it more effective for remanufacturing and, in some cases, easier to transport.
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