Plastics are a type of polymer or synthetic which is much like resins found in plants and trees. Polymers are made up of carbon string and other substances. The units in every string are called monomers. These monomers when goes through chain linking reaction then carbons join with each other forming polymer. According to dictionary meaning polymer is a complex organic compounds formed by polymerization, can be molded, extruded, formed into different shapes and films or filaments and then it is ready to be used as textile called polymer.
Plastics are of many types depending on the monomer type, length of the chains and compounds which are added to it for modifications. There are mainly two types of plastics:-
Thermoplastics
It becomes soft with heat and hard on cooling. Most of the plastics are thermoplastics. These can be reformed again and again by heating. Products made of thermoplastics can be recycled easily. Some of them are:- acrylic (Perspex) acrylo-nitrile ( nylon, polyethylene (polythene), polypropylene etc.
Thermosets
These are hardened by heating. These plastics cannot be recycled because when they are heated they will decompose instead of melting. Some of the thermosets are bakelite, epoxy, polyester, melamine etc.
General characteristics of plastics are:-
Resistant
Plastics can be resistant to chemicals. Most of the cleaning chemicals are packed into the plastics containers. It forms good containers for aggressive solvents while some plastics can be dissolved in solvents.
Thermal and electrical insulators
They can be the good thermal and electrical insulators. You must have observed in your house that all the cords, wiring, electrical appliances are covered or made up of plastics. It is also thermal insulator as in the kitchen you must have seen that the plastic is used as the handles of pot and pans, microwave cookware, insulated cups etc. Most of the jackets that are to be wore in winter are made up of polyester or acrylic.
Light weight
Plastic is light in weight and have wide range of strength depending on its application. It is used in the formation of simple toy to the construction of frame of space stations, from nylon fiber to kelvar (used in bullet proof jackets). When we compare plastics with metals like copper, aluminum or stone it is lighter in weight.
Flexible, molded, foamed
Some plastics are flexible enough that it can be stretched like ebstomers. Others can be molded to drums, bottles, parts of car etc. When mixed with some solvents it becomes paints and adhesives.
There is a wide range of characteristics of polymers which can be enhanced with the use of additives according to its application.
There are seven major plastics:-
PETE (polyethylene terephthalate)
This is tough, clear used for making containers for carbonated beverages. It can also be used in microwave trays, containers, pans, pots because it can resist heat also used in bottles, carpets, clothing etc.
HDPE (high density polyethylene)
It is very good moisture barring and chemical resistant. So it is used for packaging purposes and as containers of household and industrial chemicals like acids, bleach, detergents.
PVC (polyvinyl chloride)
It can be used for both rigid and flexible application which includes constructions, pipes, fitting etc and protects from bacteria, micro organisms and provides strength while flexible vinyl is used in wiring, synthetic leather products, blood bags, medical tubing, film and sheet etc.
LDPE (low density polyethylene)
Because it has properties of toughness, flexibility and transparency it is used in film which is used in production of bag, dry cleaning garments. It is also applicable for flexible bottle, lids, wire, cables. It has low melting point which makes it useful where heat sealing is necessary.
PP (polypropylene)
It has high melting point which makes it suitable for filling hot substances like other plastics it also resist water, acidic solutions which destruct metals. Typically it is used in yogurt containers, ketchup bottles, automobile battery casing etc.
PS (polystyrene)
It can be rigid or foamed. It has the property of transparency which makes it usable in medical and food packaging, laboratory ware etc.
There are many more plastics like nylon, polyurethanes, and copolymers etc which are used for many other purposes.
Plastics are used in variety of things because they can be made hard and tough or make rubbery, soft, light weight. Moreover they are non-rusting, hygienic and cheap.
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