- PLASTICS
Plastics are obtained from petrol-chemical products and they are moulded to shape at a very high temperature. Plastics are non-metallic objects.
Types of plastics
- Thermoplastic: these are plastics that turn to liquid when heated and they can be remoulded. E.g cups, keg etc
- Thermoset: these are plastics that do not turn to liquid when heated and they cannot be remoulded. E.g shirt buttons, plastic handle of a cooking pot or knife, cases of radio, television or telephones.
Methods of making plastics
- Injection moulding: this is the process of making nylon and hair combs.
- Compression moulding: used for making thermoset objects, e.g. Pressing Iron control knob.
- Extrusion: used for making pipes, tubes and rods.
- Calendaring: used for making buckets and cups.
Properties of Plastics
- Plastics are light in weight;
- plastics can crack easily;
- plastics cannot rust;
- plastics cannot withstand high temperature;
- plastics have high resistance to chemicals;
- Plastics are electric insulators – current cannot pass through them.
- RUBBER
Rubber is an elastic material, which regains its original shape when stretched and released. Rubber is a non-metallic object.
Types of Rubber
There are two types of rubber, viz:
- Natural Rubber: this is the type of rubber which is obtained from a white substance called LATEX obtained from trees.
- Synthetic or Artificial Rubber: this is the type of rubber which is obtained from petroleum products.
Methods of making Rubber products
- Vacuum forming;
- extrusion;
- compression moulding;
- calendaring
Properties of Rubber
- it is elastic;
- it is an insulator;
- it absorbs shock;
- it floats on water;
- it is light in weight
Uses of Rubber
- it is used for making tyres;
- it is used for making catapult;
- it is used for making rain boots;
- it is used for making rubber sandals.
EXERCISES
- What is plastic?
- Mention the names of the two types of plastics.
- Briefly describe each of the two types of plastic.
- Describe the three methods of making plastics.
- Mention 4 properties of plastic.
- What is rubber?
- Describe 2 types of rubber.
- List 4 methods of making rubber products.
- State 4 properties of rubber.
- Mention 4 uses of rubber.
Homework
- List four properties of rubber.
- Mention four uses of rubber.