Rubber is an elastic substance that is also referred to as latex or caucho. It is majorly used in elastic rubber bands, erasers, tires of vehicles, etc for its toughness, elasticity and resilience. Rubber was primarily found by Joseph Priestly, in \(1770\). This material is considered suitable for removing pencil marks from paper, and this is how it got its name ‘Rubber’.

Rubber: Definition

Rubber is a polymer that has the primary property to stretch and shrink. It is an elastomer that can come back to its original shape after being deformed. It is made by polymerisation of isoprene (\(2\) methyl-\(1, 3\)-butadiene). Natural rubber is extracted from the bark of a rubber tree. In order, to meet its huge demand, rubber was synthesized artificially, and this led to a revolution in the field of polymers. Let’s learn in detail about this magical substance.

Rubber: Chemical Name and Formula

The monomer of natural rubber is Isoprene (\(2\)-methyl, \(1-3\), Butadiene). The polymer of this isoprene is known as natural rubber, and its chemical name is ‘cis – \(1,4\) – polyisoprene’.

Rubber: Types

Based on their origin, rubbers are classified into two types: Natural rubber and Synthetic rubber. Let’s discuss them one by one:

1. Natural Rubber: It is a natural polymer extracted from the latex sap of a rubber tree. Rubber is a widely used substance due to its elasticity. Natural rubber is vulcanized, and various products are formed from this. Chemically natural rubber is known as ‘polyisoprene’. The best property of natural rubber is that it is biodegradable and a renewable resource as it is extracted from the tree. It is an essential raw material for the formation of thousands of products such as surgical gloves, medical devices, aircraft and car tires, mattresses, shoe soles, rubber boots, toys, and many more.

2. Synthetic Rubber: In the \(1890s\), with an amplified use of bicycles, there was a huge demand for rubber to make the tires of these bicycles. Thus, there was a need to synthesize them artificially to meet the increasing demand for rubber. Thus, for the first time, isoprene was polymerized artificially in the laboratory at the beginning of the \({20^{th}}\) century.

This was followed by the synthesis of rubber from butadiene. These synthetic rubbers are artificial elastomers that are synthesised from petroleum products. They have double tensile strength than natural rubber. They are primarily derivatives of \(1, 3\)-butadiene. Synthetic rubber is of two types: Homopolymer (one monomeric repeating unit) and Copolymer (more than one monomeric repeating unit).

How is Rubber Made?

1.Manufacture of Natural Rubber

Natural rubber is extracted from the latex sap of the rubber tree. The latex is collected by fixing a container on the rubber tree, and this process is known as ‘tapping’.

After this, collected latex is coagulated by adding formic acid. This process thickens them into a hard mass. These rubbers are now dried completely by using a series of rollers or simply by air drying for several days. Now, these natural rubbers are ready for processing that would further be used for manufacturing various products.

2. Manufacture of Synthetic Rubber

By polymerisation process, various synthetic rubbers are manufactured, such as the formation of neoprene by addition polymerisation, Buna-S, and Buna-N by co-polymerization, etc. Let’s learn about the formation of these synthetic rubbers in detail:

a. Neoprene: Neoprene, also known as polychloroprene, is a homopolymer and is synthesized by radical polymerisation of chloroprene. It has high resistance to oils and is used for making conveyor belts, hoses, gaskets, etc.

b. Buna-S: Copolymerisation of \(1, 3\) – Butadiene and styrene lead to the formation of Buna – S. It has high tensile strength and is a good substitute for natural rubber. It is used to make automobile tyres, footwear components, insulators of cables, etc.

c. Buna – N: Buna – N is another copolymer formed by co-polymerisation of \(1, 3\) – Butadiene and acrylonitrile in the presence of peroxide catalyst. It is resistant to oils, petrol, and some organic solvents. They are mostly used for making tank lining, oil seal, etc.

Rubber: Formation & Processing

Once rubber (natural or synthetic) is manufactured, they are sent to processor plants for processing to the final product, which can be further used for manufacturing various commodities. The four steps of processing rubber are compounding, mixing, shaping, and vulcanizing.

1. Compounding: Certain additives and chemicals are added to rubber to increase its tensile strength and enhance its properties. For example, carbon black fillers are added to rubber to increase its tensile strength and protect the degradation of rubber from ultra-violet rays.
2. Mixing: Rubber is needed to be thoroughly mixed with the additives. For this purpose, the temperature is increased and additives are mixed properly.

3. Shaping: Shaping rubber products occurs by using four general techniques: extrusion, calendering, moulding or coating, and casting. Rubbers are extruded by forcing a highly plastic rubber through a series of screw extruders. After this step, calendering passes the rubber through a series of increasingly smaller gaps between rollers.

This roller-die process combines both extrusion and calendering, producing a better product. The coating is a process to apply a coat of rubber or force rubber into fabric or other material. Tires, waterproof cloth tents, raincoats, conveyor belts, etc. are made by coating materials with rubber. Rubber products like shoe soles and heels, seals, suction cups, and bottle stops are cast using moulds. 

4. Vulcanization: Vulcanization completes the rubber-processing process. Vulcanization creates sulfur cross-connections between the polymers of rubber. Less cross-connection between the rubber polymers creates a softer rubber. Increasing the number of cross-connections decreases the elasticity of the rubber, which creates harder rubber. Without vulcanization, rubber would be sticky when hot and brittle when cold. 

Rubber: Uses

Rubber is used in different fields, such as transportation, automobiles, chemicals, agriculture, and many more. Let’s discuss them:

1. The tires and tube industries are one of the biggest consumers of rubber. Natural rubber is further mixed with synthetic products to make them more durable.
2. Rubbers are used in different automobile sectors. Natural rubber is used to make seals and different forms of padding for various automobile parts. For example, it is used to create pads of the brakes and seals of the windows and windshields of cars.
3. Rubber is used to make airbags in cars that protect riders from accidental injuries.
4. Clothing: Natural rubber in its fibrous form is elastic, which is used to manufacture tight-fitting and expandable clothing such as swimsuits and cycling shorts.
5. Flooring: Rubber is used in making flooring in many commercial places, kitchens, and even playgrounds. It provides a surface that provides padding and is both slip-resistant and waterproof. It is very easy to maintain and is long-lasting.
6. Gaskets: Gaskets are used in between two or more mechanical parts to prevent leakage or to fill irregular space between them.
7. Erasers: This rubber product could “rub” away marks made from pencils on paper, thus giving the material its name.
8. Ancient Uses: Ancient Mesoamerican civilizations used natural rubber to make waterproof shoes and bottles. Not only that but it was also used to create a sports ball in a game that is very similar to modern-day basketball, football.
9. Adhesives and Coatings: In its latex form, rubber is used as an adhesive or a protective coating for many surfaces.
10. Rubber Gloves are a very famous rubber product as using them is always preferred for keeping our hands safe and sanitary.
11. Rubbers are used to produce soundproofing materials and many rubber toys for kids.

Rubber: Summary

We can conclude that rubber is one of the most useful natural products extracted from rubber trees for humanity. With time synthetic rubber has emerged to meet the rising global demand for rubber. There are thousands of uses of rubber, and hence, it will continue to be a high-value polymer in the future also.

Frequently Asked Questions (FAQs) on Rubber

Frequently asked questions related to Rubber is listed as follows:

Q. What are the elements of rubber?
Ans: Rubber is made up of the two most common elements; they are carbon and hydrogen. The monomer of natural rubber isoprene (\(2\)-methyl-\(1,3\)-butadiene), which is a conjugated diene hydrocarbon. 

Q. Why are rubbers called elastomers?
Ans: A polymer that has elasticity is known as an elastomer. Natural rubber is an elastomer; it is made from latex, a milky rubber tree sap. Synthetic elastomers are synthesized from petroleum. Due to this property, rubber is frequently indicated as elastomers.

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