Fix the mistake: Chemical Technology and Humanity

Types and Properties of Plastics

Plastic is indispensable in modern life, including plastic bottles, bags, and electrical appliances. Let us organize its diverse types and properties.

Basic Knowledge

Plastic (synthetic resin) is a high-molecular compound (polymer) made from petroleum. It is formed when many small molecules (monomers) bond together (polymerization).
Representative types of plastic and their characteristics:
・Polyethylene (PE): Bags and film. Light and flexible.
・Polypropylene (PP): Food containers and fibers. Relatively high heat resistance.
・Polystyrene (PS): Styrofoam and plastic containers.
・Polyvinyl chloride (PVC): Water pipes and raincoats. Flame-retardant.
・Polyethylene terephthalate (PET): Plastic bottles. Transparent and strong.
For recycling identification, the material is indicated on the bottom of containers by ▲ (triangular arrows) + a number.

Important Terms
Plastic (synthetic resin) (a general term for petroleum-derived high-molecular organic compounds)
High-molecular compound (polymer) (a giant molecule formed by the polymerization of many monomers)
Thermoplastic (softens when heated and hardens when cooled. PE, PP, PET. Easy to recycle)
Thermosetting plastic (hardens when heated and does not soften again. Examples include phenolic resin)
Additives (auxiliary substances added to plastics, such as plasticizers, stabilizers, and coloring agents)
Biodegradable plastic (plastic decomposed by microorganisms. Low environmental impact)

Further Study

The major features of plastic are that it is light, rust-resistant, easy to mold, and a poor conductor of electricity. It has therefore replaced metals, glass, and wood in many uses. However, because it is difficult to decompose naturally, marine plastic pollution and the microplastic problem have become serious.
In recent years, the development of bioplastics (made from plant-derived materials) and biodegradable plastics has advanced. Efforts to reduce plastic waste through the 3Rs (reduce, reuse, recycle) are also considered important worldwide.

Key Points
  • Plastic = petroleum-derived high-molecular compound
  • PE (bags), PP (containers), PS (foam), PVC (pipes), PET (bottles)
  • Thermoplastic: softens when heated → recyclable
  • Thermosetting plastic: hardens when heated → difficult to recycle
  • Advantages of plastic: light, corrosion-resistant, easy to mold
  • Disadvantage: difficult to decompose naturally → microplastic problem
  • Measures: 3Rs, biodegradable plastics, bioplastics

Points to Note

① Distinguish between thermoplastics (such as PE and PET) and thermosetting plastics (such as phenolic resin). Determine whether they become “soft” or “hard” when heated. ② Understand the relationship between a polymer (high-molecular compound) and a monomer. ③ PET belongs to the “polyester group.” It is a recyclable thermoplastic resin.

Practice

  1. Answer the abbreviation and full name of the plastic used in plastic bottles.
  2. Explain the difference between thermoplastics and thermosetting plastics.
  3. Give one reason why plastic causes environmental problems.

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