The synthetic rubber is artificially produced by humans in an industrial area using variety of raw materials. They are available as compressed bales and square blocks. Synthetic rubber is artificial polymer (elastomer) synthesized from petroleum. It has properties of natural rubber and can add properties (like thermal stability and resistance to oils and related compounds) and can enhance the properties as required. It is possible that achieved specific properties desired for special applications by changing the composition of polymers.
At present, the use of synthetic rubber for industries is increasing rapidly.
Written by: , Chamidhu Lakpriya(undergraduate), Department of Chemical and Process Engineering, University of Peradeniya, Sri Lanka
In this tutorial, we will discuss followings.
The synthetic rubber industry has grown to its present level thanks to the effect of chemists, scientists, inventors and industrialists. Also, the scarcity of natural rubber during the first and second world wars encouraged people to make synthetic rubber.
Synthetic rubber, which had been discovered until after world war 2, spread rapidly around the world. Since then, synthetic rubber has been used in a large number of products.
The raw materials of the synthetic rubber are Butadiene, Styrene, Isoprene, Ethene, Propene, Benzene and etc. monomers. That monomers are derived from petroleum, coal, oil, natural gas, and acetylene.
This is called as 1,3-butadiene. Normally it is a non-corrosive colorless gas but can be condensed to a liquid at - 4.50C and has a mild aromatic odor. Commercial manufacturing method of butadiene is extractive distillation from crude butylene concentration (C4) stream (a by-product of ethylene and propylene production).
This is also called as vinylbenzene, ethynylbenzene, cinnamene or phenylethylene. Normally it is colorless liquid and also it has sweet smell which is vaporized easily. It dissolves with some liquids without water.
Isoprene formed as a unsaturated penta hydrocarbon. Stabilized isoprene found as a clear colorless liquid with a petroleum-like odor.
Ethene normally called as ethylene. It is a colorless gas with a sweet odor, teste and lighter than air. Commercial manufacturing method is cracking of fraction obtained from distillation of natural gas and oil.
Propene also known as propylene. It is colorless gas with a petroleum like smell. It can be produces by refining of gasoline or splitting, cracking and reforming hydrocarbon mixtures.
Benzene is colorless liquid with gasoline like smell. It is very flammable and toxic liquid. Benzene mainly produce from oil-refining as a byproduct.
Synthetic rubber is a polymer. The row materials of synthetic rubber are only monomers (Butadiene, Styrene, Isoprene, Ethene, Propene, Benzene and etc.). It is needed to convert monomers into polymers to producing synthetic rubber in industrial scale. There are two method of producing synthetic rubber on an industrial scale. They are solution polymerization and emulsion polymerization.
When we want to placement of the monomer units in the polymer molecule it can be controlled more precisely with which is conducted in solution. Usually, hydrocarbons like hexane or cyclohexane are used as a solvent. Because it is necessary to monomers are dissolve in solvent. The acceleration of the reaction induces by using catalysts such as butyllithium. The process produces low molecular weight polymers with linear shape molecular (less branching of side chains from the main polymer chain).
This is the most widely used method of manufacturing synthetic polymer. This process is taken place in water. First monomers, free-radical initiators and surfactant are added to the water. One of the ends of the surfactant is known as a hydrophilic end (water-attracting) and other end is known as a hydrophobic end (water-repelling).
These are deposited on the monomer droplet as a cover, with the water repellent end facing the monomer and the water repellent end facing the water. Other surfactants are clumped together into smaller aggregates called micelles, which also absorb monomer molecules.
Free-radical initiators are migrated into the stabilized monomer droplets (micelles) to initiate polymerization. After polymerization has reached the desired level radical inhibitors are added to stop the reaction. The resultant polymers are carried out as 'hot' or 'cold'. Hot product has more branched polymer molecules and cold has higher molecular weight but less branches.
According to how synthetic rubbers are produced, it can be categorized as styrene butadiene rubber, polybutadiene rubber, isoprene rubber, acrylonitrile butadiene rubber, chloroprene rubber, butyl rubber and etc.