Rubber- Types, Natural Rubber and its Preparation, Vulcanisation of Rubber. Uses of Rubber, Practice Problems and  FAQs

 Almost all of us have ridden a bicycle in our life haven't we? 

Have you ever wondered what would have happened if the tyres were not made up of rubber? The twists and turns of the road would have been highly treacherous if not for the elastic properties of rubber. Come to think of it, most of you would have certainly seen or used rubber in the form of balloons, gloves, erasers, conveyor belts or toys to name a few. So it begs the question. What is Rubber and how do we prepare and use it?

Rubber is a natural elastomeric polymer in which the polymer chains are held together by weak van der Waals forces. The weak forces help the polymer in regaining its shape once the deforming force is removed

Table of Contents

• Types of rubber
• Natural rubber and its preparation
• Vulcanisation of rubber
• Synthetic rubber and its preparation
• Uses of rubber
• Practice problems
• Frequently asked questions(FAQs)

Types of rubber

Rubber is an elastomer that can be obtained either naturally(natural rubber) or can be chemically produced in a laboratory(synthetic rubber-like- neoprene, butyl rubber etc). Broadly speaking, rubber can be classified into two categories namely:- 

1. Natural rubber
2. Synthetic rubber

Natural rubber and its preparation

Natural rubber is manufactured from rubber latex, which is a colloidal dispersion of rubber in water. Natural rubber is a polymer of isoprene (2 - methyl - 1, 3 - butadience) with a chemical formula (C₅H₈) is joined together forming long polymer chain of cis - 1, 4 - polyisoprene which is also known as natural rubber. India including the countries like Thailand, Indonesia, and Malaysia are one of the top natural rubber producing countries in the world.

Gutta-Percha is the trans isomer of isoprene. It is used to fill tooth cavities to prevent reinfection.    

Properties of natural rubber:

• Soluble in non-polar solvents
• Non-resistant to attack by oxidising agents.
• High water absorption capacity.

Vulcanisation of rubber

The mechanical properties like tensile strength, elasticity and abrasion resistance of natural rubber can be improved by vulcanisation. Vulcanisation consists of heating the natural rubber with 3-5% of sulphur at about 373 K to 415 K. This results in the formation of sulphur bridges between the polymer chains. Sulphur act as a cross-linking agent. When a stretching force is applied on the vulcanised rubber, the polymer straightens out but does not slip past one another because of the polysulphide bridges. When the applied force is removed, the rubber regains its original shape.

FIG: Vulcanisation of Rubber

Note: In the manufacture of tyres, 5% sulphur is used as a cross-linking agent.

Synthetic rubber and its preparation 

Synthetic rubbers are artificial rubber produced chemically mainly from petroleum by-products and natural gas. Examples of synthetic rubber include neoprene, Buna-N, Buna-S, etc,.

Neoprene: 

• It is obtained by the free-radical polymerisation of chloroprene
•  Chloroprene exhibits properties like stability to aerial oxidation, and resistance to oil, gasoline and other solvents.
• It is used in the manufacturing of shoe heels, surgical instruments, diving suits, hoses, etc. 

Buna-N:

•  It is obtained by the copolymerisation of 1, 3 butadience and acrylonitrile in the presence of high temperature and sodium catalyst.
• It is rigid and resistant to the swelling action of petrol and oils. 
• It is used in making oil seals, tank linings, etc.

Buna-S:

• It is obtained by the copolymerisation of 1, 3 butadience and styrene in the presence of high temperature and sodium catalyst. 
• It is used in manufacturing tyres, waterproof shoes, etc,.

Properties of synthetic rubber:

• Low-temperature heat resistance
•  Improvement in heat ageing 
• Excellent heat resistance.

Uses of rubber

Rubber due to its properties like- waterproof, slip-resistance nature, act as an insulator, high tensile strength, elasticity etc. it can be used for different purposes which including:

• In the automobile industry for making seats, airbags, padding in brakes etc.
• In the clothing industry to produce expandable clothes like- cycling shorts, wetsuits etc.
• In the construction industry in the form of tubes, elevator belts etc.
• In the manufacturing of consumer goods like- footwear, eraser etc.

Practice problems

Q1. Natural rubber is:

A. trans-polyisoprene
B.  Cis-polyisoprene
C. Both trans- and cis-polyisoprene
D. Neoprene

Answer: B)

Solution: Natural rubber is a polymer of isoprene (2 - methyl - 1,3 - butadience) which is also called cis-1,4-polyisoprene. 

Q2.  SBR is obtained by the free radical polymerisation of

A. 1.3-Butadiene and styrene
B. Chloroprene and styrene
C. Vinyl acetate and styrene
D. Isoprene and 1,3-butadiene

Answer: A)

Solution: Styrene butadiene rubber (SBR) or Buna-S is obtained by the free radical polymerisation of 1,3-butadiene and styrene.

Q3.  The monomer(s) of neoprene is

A. 1,3-Butadiene and styrene
B. 1,3-Butadiene and acrylonitrile
C. trans-Polyisoprene
D. Chloroprene

Answer: (D)

Solution: Neoprene is a type of synthetic or artificial rubber obtained by the free-radical polymerisation of chloroprene.

Q4.  Which of the following is not synthetic rubber?

A. Buna-S
B. Cis-Polyisoprene
C. Buna-N
D. Neoprene

Answer (B)

Solution: Cis-Polyisoprene is a natural rubber which is formed by the polymerisation of isoprene (2 - methyl - 1, 3 - butadience). Whereas, Buna-S, Buna-N and Neoprene is a synthetic rubber formed by the polymerisation of 1,3-butadiene and styrene,  1, 3 butadience and acrylonitrile and chloroprene respectively.

Frequently asked questions(FAQs)

Question 1.  What is the full form of EPDM rubber and its use?
Answer. EPDM stands for ethylene propylene diene monomer a synthetic rubber polymer and is made from ethylene and propylene monomers. This rubber was developed in the early 1960s and used to produce a variety of products like a radiator and steam hoses, tires, freezer gaskets, brake systems in automotive, pool and tankers liners roofing membranes and aircraft seals to name only a few.

Question 2.  What are copolymers? Explain it using an example.
Answer: Copolymers are those types of polymers which is formed from the polymerisation of two different types of monomers. For example, terylene also known as dacron (ethylene glycol and terephthalic acid) is a monomer and Nylon-6,6 in which (Hexamethylene diamine and adipic acid) is a monomer.

Question 3. What are the important characteristic properties of synthetic rubber that have an advantage over natural rubber?
Answer:  Important characteristics of synthetic rubber that have an advantage over natural rubber includes:

• Betterweathering and ageing
• More resistance to oil
• Resistance to chemicals, oxygen, ozone, and certain solvents
• Resilience over a wider temperature range

Question 4. Why rubber is generally referred to as elastomers?
Answer:  Rubbers are generally referred to as an elastomer because these polymers on stretching can revert back to their original shape when an external force is removed. It also has the ability to stretch to 10 times its original length.

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