Synthetic polymers are commonly called plastics. The term plastic comes from the Greek word plastikos, which means to mould. Nowadays, plastics refer to synthetic materials which can be softened by heat or pressure, and then moulded into any desirable shape.
Thermoplastics and Thermosets
Plastics are either
- Thermoplastics or
Thermoplastics can be softened repeatedly by heat and remoulded. Thermosets, however, cannot be softened or melted by heat and remoulded once they are formed or set.
The table below differentiates thermoplastics from thermosets based on their different chemical products
|Polypropene||Urea – methanal|
Desirable Properties of Plastics
Practically everything around us is made of some type of plastic. The following factors have made our present plastic age possible.
1. Plastics have properties which make them suitable for many purposes. Plastics are strong but light; inert to air, water, and other chemicals; resistance to fungal and bacterial attacks; and good insulators of heat and electricity.
2. Plastics can be tailor-made to our exact requirements. They can be made into hard, rigid blocks; thin, flexible sheets; fibres that can be made into ropes and fabrics; and very light foams. They have wide applications.
3. Raw materials for the manufacture of plastics are readily and cheaply available from the refining of crude oil. The boom of the oil industry has contributed greatly to the growth of the plastics industry.
4. Plastic items can be manufactured at very low costs by using moulds and automated manufacturing processes.
Problems Associated With the Use of Plastics
There is a heavy dependence on crude oil, since petrochemicals provide the balk of the raw materials needed for making plastics. This poses a problem as the world’s supply of crude oil is limited. Alternative energy sources that are being explored do not provide the raw materials needed for making plastics.
Most plastic materials are non-biodegradable and cannot be broken down by microbial action into simple inorganic forms. Therefore, they cause severe land pollution problems since they are not easily disposable. Burning plastic objects would not be a good alternative as this would liberate toxic vapours or gases into the atmosphere.
How to Make Synthetic Polymers
Synthetic polymers are made by the polymerization of monomers. For polymerization to occur, heat and the presence of a chain-initiating substance called an initiator is required.
Polymerization is the process whereby two or more monomers link together to form a compound of high molecular mass called the polymer.
There are two kinds of polymerization