NEET Chemistry Notes Polymers – Vulcanisation of Rubber
Vulcanisation of Rubber
Vulcanisation of Rubber
- Natural rubber becomes soft at high temperature (>335 K) and brittle at low temperature (< 283 K). It has high water absorbing capacity. It is easily attacked by oxidising agents and soluble in non-polar solvents.
- To improve these properties, vulcanisation of rubber is carried out. The process involves the heating of raw rubber with sulphur and appropriate additive at a temperature 373 – 415 K.
Sulphur forms cross-links at reactive sites of double bonds and makes the rubber stiffened. Rubber made with 1-3% sulphur is soft and stretchy and rubber made with 3-10% S, is more rigid (used in making tyres).
Polyolefins
These are obtained by the addition polymerisation of ethylene and its derivatives.
Polythene
Polymer of ethylene or ethene.
Low density polythene (LDP)
It is tough, flexible, transparent, chemically inert as well as poor conductor of electricity. It has moderate tensile strength butgood tearing strength.
It is used in the insulation of electricity carrying wires and manufacture of queeze bottles, toys and flexible pipes.
High density polyethylene (HDP)
It has high density due to close packing. It is also chemically inert and more tougher and harder. It is used for making containers, house wares, bottles, toys, electric insulation etc.
Polystyrene (Styrone)
The monomers are styrene molecules. It is thermoplastic. It is used for making toys, radio and TV cabinets.
It is used for making rain coats, toys, electrical insulation. It is hard and resistant to heat and chemicals.
Polypropylene (PP)
It is obtained by polymerising propylene in the presence of Ziegler-Natta catalyst.
Polytetrafluoroethene(teflon)
It is chemically inert and resistant to attack by corrosive reagent. It is used in making oil seals, gaskets and also for non-stick surface coated utensils.
Polyacrylonitrile
It is used as a substitute for wool in making commercial fibres as orlon or acrilan.
Polyamides
The polymers which contain an amide linkage in chain are known as polyamide, e.g. nylon-6,6.
Nylon-6,6
It is obtained by the condensation of adipic acid and hexamethylenediamine with the elimination of water molecule.
In the above case, the carbon atoms are 6 in each case, therefore the product is described as nylon-66.
Properties and Uses
Nylon-6,6 is a linear polymer and has very high tensile strength. It shows good resistance to abrasion. Nylon-6,6 is usually fabricated into sheets. It is used in bristles for brushes and in textile.
Nylon-6
Nylon-6 is obtained by heating caprolactum with water at a high temperature.
