Plastic recycling process

Published at

You will have noticed in your everyday life that there are many different types of plastics and that many can be recycled. But how is plastic recycled and what is the plastic recycling process?

Ways to recycle plastic

There are two processes for recycling plastics, but for all of them, the first step is the separate collection of plastics at source by consumers. All packaging that ends up in the yellow bin is transported to sorting plants, and from there to their respective recyclers. In a more developed way:

  • ·      First the materials are separated according to whether they are suitable or unsuitable. For example, labels, debris or soils of some kind are discarded. This process can be somewhat complex, as at least three fractions are separated: metals (steel and aluminium) 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 bag would be mixed plastic.
  • ·      On the other hand, they are also segregated according to colour. In this way, the use of dyes is optimised.
  • The pieces are broken and crushed into small pieces to facilitate processing.
  • · They are then washed, covering the pieces with water and allowing the denser impurities to remain below.
  • · They are dried and centrifuged, removing any remaining impurities.
  • · It is then compacted and stored. Once in the recycling plant, the plastic is sorted according to its physical characteristics.

There are two forms of plastic recycling process: mechanical recycling and chemical recycling.

Mechanical recycling

The plastic recycling process can be used for thermoplastic plastics.

Once shredded, washed and dried, the plastic is stored in a large silo, where it will be mixed by a mechanical process, until a homogeneous material in colour, texture and behaviour is obtained, ready for extrusion.

Extrusion: The central body of the extruder consists of a long barrel which, by means of the heat and friction of its interior axis, allows the plasticising of all the particles previously created, giving rise to a uniform mass. In this way, the polymers are melted by heat. In this section is when we add the necessary colour 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 will retain any type of impurities that the previous processes may have left adhered to the material: cardboard remains, small pieces of wood, fabric or other pieces of incompatible materials. When these screens become dirty, they are automatically replaced by clean ones.

Pelletising: The plastic comes out of the head of the extortion machine in the form of monofilaments or threads which, in contact with the water deposited in the tub, cool down. The yarns are then passed to the nozzle, where they are cut by a rotating blade. From this process we obtain the appropriate grain or chippings required by companies that shape this plastic.

Once this process is finished, the chippings are melted and the plastic is given a new shape, depending on the method used, in the form of sheets, solidifying in a cold mould, in the form of hollow pieces by introducing air inside them or using pressure moulds.

Chemical recycling

This type of plastic recycling process 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 plastic materials are degraded by heat or catalysts to the point where the macromolecules are broken down and only simple molecules, commonly called monomers, remain. From these monomers, other types of plastics or fuels could be obtained depending on the technique used.

Of the two ways of recycling plastic, this is the least used, although it is the most promising, since by obtaining basic monomers, plastics of the same quality as the original ones can be made again.

The result of these processes are resin pellets that can be fed into machines that produce plastic objects, such as bottles or boxes.

Uses of recycled plastic

  • ·      Plastic wood: for the creation of urban furniture (benches, fences, etc.).
  • ·      Textile fibre: 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 again coded as recyclable plastic. It is quite possible that the bottle you throw away in the yellow bin will end up as a new bottle.

At SINTAC all polymers are recycled, thus contributing to the circular economy.

Featured Articles