Rubber
Rubber is the name given to elastic, high molecular compounds capable of changing their shape
(deforming) when acted upon by an external force and of rapidly resuming their original shape
when the force is removed.
If sulphur is added to natural rubber which is then heated, the sulphur will form links between the
linear macromolecules of the rubber, i.e. from bridges between them; by these larger
macromolecules a web structure will be produced. This is called vulcanization of the rubber, and
the product of reaction between the sulphur and rubber is vulcanized rubber.
Natural and synthetic rubber is the basic material in fabrication of rubber textile and rubber
material articles which are so extensively used in various branches of economy.
Used in motor car and aircraft tyres, drive belt and conveyer belts, flexible hoses and sleeves,
machine parts and various gaskets, electric insulation materials, rubberized fabrics and rubber
footwear, articles of personal hygiene and many other rubber products.
Rubbers are classified as natural and synthetic rubber.
Natural rubber:
Natural rubber can be produced from many plants, however actually the latex is obtained from
small number so called rubber plants.
Ex. Hevea brasillinsis (latex 20-35%)
Synthetic rubber:
Made from one individual monomer by addition polymerization or from a blend of two or three
monomers by co polymerization.
Styrene-butadiene rubber:
Styrene-butadiene rubber (SBR) comprises more than half of worlds production of synthetic
rubber and exceeds natural rubber supply.
Raw materials:
The principle raw material for SBR manufacture are monomers, styrene and butadiene. Other raw
materials are oils used for extending soaps, antioxidants, short stopping agents, coagulating agents,
catalysts, modifiers, water and hydrocarbon solvents.
Manufacturing:
Different ratios of styrene and butadiene can be used but the ratio mostly used is styrene 25% and
butadiene 75%. If the percentage of styrene is increased to 50% or above, a tough product- a rein
forcing resin is obtained. SBR is obtained mostly by emulsion polymerization using free radical
catalyst.
Polymerization at 5-10°C is called cold process and the product is called cold SBR while the one
made at 50°C is called hot SBR. The cold initiators are redox combinations such as p-methane
hydroperoxide/ferrous sulphate which result in higher molecular weight at lower temperatures.
Hot processes use initiators such as potassium persulphate. There is higher degree of branching.
Cold SBR gives better abrasion resistance and dynamic properties. Higher molecular weight
obtained also allow higher levels of oil extension.
The process involves 20% aqueous caustic purification of fresh plus recycle monomers, followed
by consecutive passage through 6-12 glass-lined or stainless-steel reactors. The total residence
time ranges from 5-15 hours and reactors are equipped for steam heating, water cooling, and
refrigeration.
Flow sheet for manufacture emulsion of styrene-butadiene rubber (SBR)
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