Rubber: Important component of Polymer

Rubber is made from the latex (milk of the Evergreen Forest tree). It is an elastomer, a polymer which regains its original shape and possesses high elasticity. It is a tough polymer which has high resistivity to withstand the weather and chemical attacks.

Types of rubber

Rubber can be categorized as natural rubber, or synthetic rubber. Many substances, such as butyl rubber, Thiokol, or neoprene are used as synthetic rubber. An elastomer must have high molecular weight and a flexible polymer chain.

Natural Rubber

Natural rubber is one of nature's unique materials founded by Christopher Columbus's. Before that the Indians use to make balls of rubber by smoking the milky, white latex of trees of the genus. Later it was used in waterproofing shoes, garments etc. Crude rubber possessed the properties of elasticity, plasticity, strength, durability, electrical non conductivity, and resistance to water. The other name of natural rubber was “gum- elastic”.

The first commercial use of natural rubber was as a waterproofing material. Later on it was used for moulding. The major use of natural rubber was made in weaving waterproof garments in which a thick coal tar naphtha solution of rubber was used.  

Crude rubber is basically a hydrocarbon having the chemical formula C5H8, along with 2 to 4 percent protein and 1 to 4 percent acetone-soluble materials (resins, fatty acids, and sterols). According to Faraday's analysis natural rubber is obtained from the pure monomer, which he named isoprene .The molecular weights of rubber molecules range from 50,000 to 3,000,000. Sixty percent of the molecules have molecular weights of greater than 1,300,000. 

Vulcanization

The natural rubber is thermoplastic in nature and becomes soft and sticky in summer and hard and brittle in winter. This problem encouraged scientists for further developments.

A sample of rubber mixed with sulphur and litharge (lead oxide, PbO) on a hot stove gave birth to rubber like material which is heavily cross-linked, insoluble, and infusible, thermosetting polymer or "thermoset." The process is called "vulcanization". Later on sulphur to convert natural rubber into ebonite, the first thermosetting plastic.

Synthetic Rubber

The development of a synthetic rubber was a slow process and it was used in more quantity.

• Carl Marvel, a German scientist mixed polymerized 3-methylisoprene (2,3-dimethyl-1,3-butadiene) units, (CH ₂ = C(CH ₃ )C(CH ₃ ) = CH ₂ ), obtained from acetone, to form an inferior substitute called methyl rubber. The USSR was the first country to produce first synthetic rubber industry.
• Another product Thiokol, a rubbery polysulfide condensation product of ethylene dichloride and sodium tetrasulfide was founded which is still used for gaskets, sealants, sealer adhesives, and hoses.
• Neoprenes are having high tensile strength, high resilience, and excellent resistance to oxygen, ozone, other chemicals, and oil. They resist heat, flame, tearing and are good general-purpose rubbers, but because of high cost, their use is limited.

Other Synthetic Rubbers

• Synthesized butyl rubber via the copolymerization (polymerization of a mixture of monomers) of isobutylene (2-methylpropene (CH ₃ ) ₂ C = CH ₂ ) with a small amount of isoprene is used  as synthetic rubber.
• Buna rubbers are oil-resistant Buna S (S for styrene) and Buna N (N for nitrate). Buna S, styrene butadiene rubber, is currently called SBR, and it is produced at about twice the volume of natural rubber, making it the most common synthetic rubber. Buna N, Acrylonitrile-butadiene rubber, is now called NBR. 
• BR (for butadiene rubber), a rubberlike polymer that is almost exclusively cis -1,4-polybutadiene, when blended with natural or SBR rubber, has been used for tire treads.
• Polyurethane (PU), a polymer is used for rigid and flexible foams, bristles, coatings and automobile parts, such as bumpers.

Although natural rubber performs well for most uses, some of the newer synthetics are superior to it for specialized purposes. Today rubber is indispensable for a variety of products and industries, and our modern world, with its many necessities and luxuries, would be unthinkable without it.