Chemistry in Everyday Life (Rubber)

Natural Rubber
Natural rubber is an excellent example of a natural polymer and an elastomer in particular. Elastomers are substances that can be readily stretched. They retract rapidly to their original form when released. It undergoes long range reversible extension under relatively small applied force. This elasticity makes it valuable for variety of uses. Natural rubber is also called plantation rubber.
Preparation
Latex, the white milky liquid obtained by making a cut in the rubber tree contains 30%-40% of rubber and is a colloidal solution of rubber in water. This is coagulated (changed from fluid to solid state or clotting) with acetic or formic acid and can then be squeezed, rolled, milled and vulcanized.
Vulcanization of Rubber
Charles Goodyear discovered the process of vulcanization in 1893 to modify the properties of natural rubber. Vulcanization is the addition of right amount of sulphur to natural rubber to impart high elasticity, tensile strength and resistance to abrasion.
Synthetic Rubbers
Synthetic rubbers are made by the polymerization of dienes, in the presence of Zeigler-Natta catalyst. These rubbers are tougher, more flexible and more durable than natural rubbers.
Polymerization of 1,3 - butadiene
Synthetic rubbers are either homopolymers of 1,2-butadiene derivatives or are copolymers in the formation of which one of the monomers is 1,3-butadiene or its derivative so that the polymer has the availability of double bonds for its vulcanization.
Synthetic or artificial rubbers are also polymers. They are not natural rubbers and are superior to natural rubber.
Neoprene or Polychloroprene
The first commercially successful rubber substitute, manufactured in the US is neoprene (1931). It is prepared by the polymerization of chloroprene (2-chlorobutadiene).
Properties of Neoprene
Neoprene is superior to natural rubber because of the following properties:
- Neoprene is non-inflammable but natural rubber ius inflammable.
- Neoprene is resistant to oils, organic solvents, petrol and grease. Natural rubber swells and rots in contact with these materials.
- Neoprene is stable even at high temperatures. Nutrual rubber retains its usefulness only over a low range of temperatures.
- Neoprene does not require vulcanization like natural rubber.
- Neoprene is resistant to the action of oxygen and ozone. Natural rubber deteriorates when exposed to oxygen.
- Neoprene is a thermoplastic. It need not be vulcanized but can be compounded with other suitable ingredients like magnesia, wood resin and zinc oxide before using.
Uses of Neoprene
Neoprene is used for making transmission belts, printing rolls and flexible tubing for carrying oil and petrol. It is also used as insulator making conveyor belts and printing rollers.
Biopolymers
Nature has many polymeric species which are essential for life and are called biopolymers. Polysaccharides, proteins and nucleic acids are examples.