Plastics are versatile and flexible materials. All plastics are based on polymers and they are created by bonding molecules together.The terms monomer and polymer are very important in the plastics industry. A monomer is a relatively small molecule that can chemically bond to other monomers, forming a polymer. All plastics are polymers.
A MONOMER is a small molecule that combines chemically to other monomers to form a polymer
Example - derived from oil - a hydrocarbon ethylene molecule(seen opposite). Many modern plastics are manufactured from oil.
An ethylene monomer forms a’ long chain monomer’ due to individual ethylene monomers joining together. This produces the polymer - polyethylene. This is a thermoplastic and is useful in the manufacture of 'plastic' bottles.
Once 'set' these plastics cannot be reheated to soften, shape and mould. The molecules of these plastics are cross linked in three dimensions and this is why they cannot be reshaped or recycled. The bond between the molecules is very strong.
These plastics can be re-heated and therefore shaped in various ways. They become mouldable after reheating as they do not undergo significant chemical change. Reheating and shaping can be repeated. The bond between the molecules is weak and become weaker when reheated, allowing reshaping. Thermoplastics tend to be composed of 'long chain monomers'. These types of plastics can be recycled.
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