Plastic recycling process
You will have noticed in your everyday life that there are many different types of plastics and that many of them can be recycled. But how is plastic recycled and what is the plastic recycling process?
Ways to recycle plastics
There are two methods for recycling plastics, but in all of them, the first step is the separate collection of plastics at the source by consumers. All packaging that ends up in the yellow bin is transported to sorting plants and from there to the respective recyclers. In an advanced process:
- First, the materials are separated according to suitable or unsuitable. For example, labels, debris or any dirt are sorted out. This process can be a bit complex, as at least three fractions are separated: metals (steel and aluminum) and plastics (PET, HDPE, film, and mixed plastic). A water bottle would be PET plastic, a soft drink can would be metal and a potato sack would be mixed plastic.
- On the other hand, they are also separated by color. In this way, the use of dyes is optimised.
- The pieces are broken and crushed to make them easier to process.
- They are then washed, covering the pieces with water and allowing the denser impurities to remain at the bottom.
- They are dried and centrifuged, removing any remaining impurities.
- It is then compacted and stored. Once at the recycling plant, the plastic is sorted according to its physical properties.
There are two types of plastic recycling processes: mechanical recycling and chemical recycling.
Mechanical recycling
The plastic recycling process can be used for thermoplastics.
After the plastic has been crushed, washed, and dried, it is stored in a large silo, where it is mixed through a mechanical process until a homogeneous material is obtained in color, texture, and behavior, ready for extrusion.
Extrusion: The central body of the extruder consists of a long cylinder which, due to the heat and friction of its inner axis, allows the plasticization of all previously formed particles, creating a uniform mass. In this way, the polymers are melted by heat. In this section, we will add the necessary color that our customers demand to meet their needs.
Filtering: With the necessary texture and fluidity, the plastic goes through a filtering process – a system of very fine meshes – that retains all kinds of impurities that have stuck to the material during the previous processes: cardboard scraps, small pieces of wood, fabric or other pieces of incompatible materials. If these screens are dirty, they are automatically replaced with clean ones.
Granulation: The plastic comes out of the head of the extrusion machine in the form of monofilaments or threads, which cool down in contact with the water deposited in the tank. The threads are then guided to the nozzle, where they are cut by a rotating blade. From this process, we obtain the appropriate grain size or chips needed by the companies that mold this plastic.
Once this process is complete, the chips are melted and the plastic is given a new shape, depending on the process in the form of plates that solidify in a cold mold, in the form of hollow bodies by introducing air into the interior or by pressure molding.
Chemical recycling
This type of plastic recycling consists of breaking down the large molecular chains that make up plastics into simpler molecules that serve as raw materials for the chemical industry.
The plastics are degraded by heat or catalysts to such an extent that the macromolecules are broken down and only simple molecules, so-called monomers, remain. Depending on the technique, other types of plastics or fuels can be obtained from these monomers.
Of the two ways of recycling plastics, this is the least used, although it is the most promising, as the extraction of base monomers allows plastics to be produced again in the same quality as the original ones.
The result of these processes is resin granules that can be fed into machines that produce plastic items such as bottles or boxes.
Uses of recycled plastic
- – Plastic wood: for the production of street furniture (benches, fences, etc.).
- – Textile fibers: for clothing, carpets, ropes, etc.
- –Bottles: Most bottles are recycled back into more bottles.
- –Construction: Bricks, pipes, fences, etc.
If you're wondering what the recycled plastic is used for after all this plastic recycling, think of almost any bottle, box, can, or toy that is labeled as recyclable plastic again. It's entirely possible that the bottle you throw away in the yellow bin will end up as a new bottle.
At SINTAC, all polymers are recycled, contributing to the circular economy.