The process of making plastics

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Plastics can be divided into two major categories: thermoplastics and thermosets. Thermoplastics can be remelted and reformed many times into different shapes. For this reason, they are the most commonly recycled plastics. Thermosets can only be formed once. After that, they may be ground and used as filler for future plastic products. Thermoplastic resins are the primary focus of this report because they are more readily recycled. The major categories of thermoplastic resins are high-density polyethylene (HDPE), low density polyethylene (LDPE), linear-low density polyethylene (LLDPE), polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC). Of the different types of products, the plastics recovered from the waste stream for recycling are mostly those used in packaging.

Virgin plastic resins are produced in large-capacity facilities from the monomers that are the building blocks to plastic polymers. Oil and natural gas are the main raw materials for producing the monomers. Other natural resources such as wood and coal can be used, but this is not common. Four per cent of annual world oil production is used as a feedstock for making plastics, in addition to the four% used as energy to process plastics (Wastewatch, 2001). Extracted oil is made up of a mixture of hydrocarbons, which can be separated into fractions, such as gasoline, naphtha and bitumen. Some of these can then be processed, by cracking or reforming, into compounds that provide the starting material for the petrochemical industry to produce materials such as plastics and synthetic rubber.

The monomers undergo polymerisation to form the polymer. Additives can be added to the resin pellets to achieve desirable properties. Only minor changes in chemical structure can lead to significant changes in the material characteristics. The fact that additives can change the characteristics of the polymer considerably has made plastics a very versatile and widely used material. For example, PVC is thermally unstable, so stabilisers and lubricants are added in a compounding process. This produces rigid PVC. Flexible PVC is made with the addition of plasticisers. A wide variety of additives are used to help in further processing. Unfortunately, as discussed below, these additives can make recycling difficult and lead to a substantially increased cost of doing so.

Figure 3.1. Flow diagram of plastic cycle43

Monomer

Synthetic Resin

Plastic Products

Plastic

Figure 3.1. Flow diagram of plastic cycle43

Monomer

Synthetic Resin

Diagram For Making Plastic Pellets
Waste disposal

Figure based upon van Beukering (2001).

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Responses

  • Hagosa Yohannes
    How to make plastic pellet from used material?
    9 years ago
  • ari-pekka
    How plastics are produced digram?
    8 years ago
  • Rosa
    How plastic is made diagram?
    8 years ago
  • erwin
    What hydrocarbon is a major feedstock in making plastics?
    8 years ago
  • Swen
    What chemical is a major feedstock in making plastics?
    6 years ago
  • haben
    What chemical is a major feedstock in making plastic?
    6 years ago

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