PET is light, clear or transparent with high gloss (sparkling 'crystal clear'), hard and wear-resistant. It is also a good barrier to gases.
Polyethylene (= Polythene) is synthesised from ethylene. It is among the most important and versatile of the hundreds of commercial plastics. Polyethylene is usually translucent, tough and unaffected by water and a large range of chemicals. It is used in a wide variety of applications, because it can be produced in many different forms.
The three general classifications of this plastic are low density, medium and high-density polyethylene.
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HDPE (High-Density Polyethylene)
HDPE has little or no branching. This allows the molecules to be tightly packed, which makes it rigid. Therefore it is used in applications where rigidity is important. HDPE is easy to process, cheap, and highly resistant to chemicals.
A negative point is that toxic fumes are produced when HDPE is burnt.
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PVC (Polyvinyl chloride)
PVC is made up of vinyl chloride. The plastic can be rigid or flexible, and is durable, weatherproof, and strong. Maximum temperature for PVC is 60oC; under 0oC it becomes brittle. PVC has outstanding resistance to alcohol’s, water, concentrated acids, alkalis, petrol and oil. It is not resistant to aromatic solvents.
PVC is, in principal, an indestructible plastic unless it is burnt, but then toxic hydrochloric acid is released.
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LDPE (Low-Density Polyethylene)
The LDPE polymer is largely branched, which forces the molecules to be packed rather loosely - the material that is formed has a low density. This makes LDPE soft and pliable. At the same time it is durable, weatherproof, tough at low temperatures, easy to process, cheap, and it has excellent chemical resistance. LDPE melts at a lower temperature than HDPE.
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PP (Polypropylene)
Propylene is the monomer that will form polypropylene: propylene gas is polymerised in the presence of a catalyst. The plastic is tough, lightweight has a smooth surface that cracks when bent, and does not scratch easily. Polypropylene is also an effective barrier against water vapour.
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PS (Polystyrene)
Styrene is the primary raw material from which polystyrene is made. Polystyrene foam packaging has air blown into it - only about five percent of a foam package is polystyrene and the rest is air (this makes the plastic white). Therefore polystyrene is a good insulator and can hold food or drinks at a desired temperature. Polystyrene is also able to absorb shocks, protects against moisture, and is resistant to staining. However, it is brittle and crumbles easily.
