Polymeric Materials
The world polymer is derived from two Greek words, poly and meros. The word, poly, means multiple or many and the word, meros, means parts or units. Therefore, the word, polymer, means a group of many units.
Polymeric materials are composed of a number of small units called monomers interconnected with each other.
Polymers can be defined as substances that are formed by combining a number of monomers. Monomers are joined together by using bonds formed between carbon molecules.
Polymers are formed through the process of polymeration. In this process, monomers undergoes a chemical reactions. As a result of these reactions, monomers bind together to form polymers.
For example when the monomer, tetrafluoroethene, is polymerized, polytetrafluoroethene, which is commonly known as Teflon, is formed. The polymer, Teflon, has wide range of applications i.e. frying pans, sauce pans.
A commonly used polymer is plastic. Plastics and rubbers development began much earlier.
A broad definition of plastic is any non metallic material that can be moulded into desired shape.
Polymers Types and Characteristics
● Types of polymers
1) Thermoplastic Materials
2) Thermosetting Materials
3) Elastomers (Rubber)
General characteristics of plastics are as follows -
1. They are versatile i.e. can easily be formed into very complex shapes
2. They are relatively inexpensive
3. Many processes are easily automated
4. They have high strength to weight ratio
5. They can quickly produce a lot of parts
6. They have good insulation properties, thermal as well as electrical
7. They have good corrosion resistance
8. They can be made transparent or easily colored
9. They are capable of being foamed i.e. lightweight and flexible
Properties and uses of Thermoplastics, Thermosetting Plastics and Rubbers.
Thermoplastic Materials
1. Thermoplastic Materials are those which soften on application of heat and can be set into desired shape on cooling.
2. They can be re melted again and again on successive application of heat.
3. When thermoplastics are heated they become softer and less stiff until they become viscous liquids. On cooling the original properties return.
4. Generally they are heated with pressure and no chemical reaction takes place only physical change takes place.
Thermosetting Materials
1. Plastics which become soft on application of heat and become hard by chemical change are known as thermosetting plastics.
2. They cannot be softened again by application of heat.
3. Thermosetting plastics are those substances which undergo a definite chemical change during the moulding process, causing them to become permanently rigid and incapable of being softened again.
4. The process is not reversible.
5. Typical thermosetting materials include phenolics, ureas, melamine, epoxides and polyesters. Some thermosetting resins when mixed with long glass fibres are called Glass Reinforced Plastics.
Elastomers (Rubber)
1. Elastomers are polymers which are characterised by very high elasticity (five to ten times of original length) but a very low modulus of elasticity, and the capacity for very large rapidly recoverable deformation. For example, rubber band.
2. A rubber/elastomer is a polymeric material with long flexible molecular chains and the ability to deform elastically when vulcanised.
3. During the vulcanising process, rubber molecules are linked with adjacent molecules at intervals along their lengths, usually by sulphur to form a cross-linked elastic material which is stable over a wide range of temperatures.
4. Typical elastomers are chloroprenes i.e neoprenes, Here chemical name is chloroprene and trade name of rubber is neoprene.
