Polymers & Rubber

Polymers

» The word polymer comes from two Greek words; ‘poly’ means many and ‘mer’ means unit or part. So, a polymer is made up of many repeating units. These are used to manufacture plastic toys, cups, buckets, synthetic clothing materials, machine parts, automobile tyres, gears and seals, electrical insulating materials, etc.

» Polymers are the backbone of four major industries; plastics, fibres, elastomers, paints, and varnishes.

» A polymer is a compound of high molecular weight formed by the union of a larger number of molecules of one or two types of low molecular weight (known as monomers), and the process involving the formation of a polymer is called polymerization.

Plastics

» These are cross-linked polymers (a substance having high molecular weight and repeating unit) and are very tough.

» Lae is natural plastic (polymer).

These are two types :
1. Thermoplastics are the polymers which can be easily soften on heating, e.g., polythene, polystyrene, polyvinyl chloride, Teflon, etc.

2. Thermosetting plastics are the polymers which undergo permanent change on heating due to excessive cross-linking. These cannot be reused, e.g., Bakelite.

Fibers

They have strong intermolecular forces like hydrogen bonding, e.g., nylon-66, Dacron. Orion, etc.

Natural Rubber

» Natural rubber is a linear polymer of isoprene (2-methyl-l, 3-butadiene). It is also called c/s-1, 4-polyisoprene. It is obtained from latex from the bark of rubber tree.

» Vulcanization of rubber is heating of rubber with sulphur. It makes rubber hard, strong and more elastic.

» Rubber made with 1-3% sulphur is soft and stretchy and used in making rubber bands, while rubber made with 3-10% sulphur is more rigid and is used in the manufacturing of tyres.

» Synthetic rubber was discovered by Mathews and Harris. Neoprene, Buna-N, Buna-S, and thiokol are some examples of synthetic rubber.

» Neoprene (Polychloroprene) has a superior resistance to vegetable and mineral oils. It is used for manufacturing conveyor belts, hoses, and gaskets.

» Buna-N is a copolymer of butadiene and styrene. It is resistant to the action of petrol, lubricating oil, and organic solvents. It is used in making oil seals, tank lining, etc.

» Buna-S is a copolymer of 1, 3-butadiene and styrene. It is also known as SBR. It is used in the manufacturing of automobile tyres, rubber soles, etc.

Rayon

It is semisynthetic polymer (obtained from natural polymers). It is obtained by chemical treatment of wood pulp (cellulose). It is also known as artificial silk because its properties are similar to that of silk. It is mixed with cotton to make bed sheets or mixed with wool to make carpets.