Use Of Plastics In Construction | Types Of Plastics And Their Properties

 PLASTICS

Plastics are basically organic substances that may be natural or synthetic resins in origin with or without moulding compounds. Synthetic resins are phenol, formaldehyde, cellulose, vinyl, alkyd, etc. The moulding compounds are catalysts, fillers, hardeners, lubricants, pigments, plasticisers, solvents, etc.

 

Types of Plastics and their Properties

Plastics may be classified into two broad groups based on their behaviour with respect to heat, viz., thermoplastics and thermoset plastics.

 

1. Thermo Plastics

These are the plastics that become soft when heated and become hard when cooled. These plastics can sustain repeated softening and hardening for an indefinite time. Old scrap and worn-out materials of this type can be effectively used again.

Some of the important thermoplastics are acrylic, cellulose acetate, polythene, perspex and polyvinyl chlorides.

Acrylic contains methyl methacrylate. Acrylics are transparent, rough and strong and withstand impacts. It is used for doors, windows and as safety glass in automobiles and aircraft.

Cellulose acetate is made from cottonseed. It is used for electric cables, handrails, etc.

Polythene is transparent and chemically unaffected by temperature and moisture. This is mainly used for preparing pipes, covers, waterproof packing, etc.

Perspex is strong enough and is made in the form of sheets. This is used for electrical fittings for decorative purposes.

Polyvinyl chloride (PVC) is a product obtained from vinyl chloride and acetate. It is acid-proof, light and withstands wear and tear. It is used for drainage pipes, floor finishing, etc.

 

2. Thermoset Plastics

These plastics become rigid due to chemical changes when moulded under pressure and temperature. These plastics once cooled and take form, can not be changed further due to the application of heat.

Some of the commonly used thermoset plastics are phenol-formaldehyde, phenol furfuraldehyde, urea formaldehyde and bakelite.

Phenol formaldehyde is formed by heating phenol and benzene with a suitable catalyst. Phenol furfuraldehyde is formed by digesting husks of rice, oat, groundnut with sulphuric acid, distilling the mixture to separate the furaldehyde vapour and then permitting the vapours to chemically react with phenol with a suitable catalyst.

Urea-formaldehyde is formed by reacting urea with formaldehyde in the presence of a catalyst.

Bakelite is made by heating an equal amount of phenol and formaldehyde with a base. This is orange in colour which is used with fillers to form different materials.

Thermoset plastics are used for various purposes such as dishes, plates, cabinets for electrical appliances, etc.

 

Uses of Plastics

1. They are clean, light in weight and have shining and attractive surfaces.

2. They have resistance to corrosion, vermin attack and other atmospheric effects.

3. They act as good heat and electrical insulators.

4. They have easy workability.

5. They need no painting or polishing.

6. They are available in different colours and different degrees of transparency.

7. Some plastics have high compressive strength.

8. They have good adhesiveness capacity.

9. They are good at absorbing shocks and vibrations.

10. They are cheap and freely available.

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