Natural Rubber and Synthetic Rubber: Definition and History

Every day we use products that have, as one of their ingredients, rubber; seldom, however, do we consider the science involved. From the tires gripping the road beneath our cars to elastic bands that help bind our papers together, rubber plays an indispensable role in our lives. It's a material that brings comfort, safety, and functionality whether in the soles of our shoes, the seals in our refrigerators, or even protective gear.

This Story also Contains

1. Understanding Natural and Synthetic Rubbers
2. Natural rubber:
3. Vulcanization of rubber
4. Types of Synthetic Rubber
5. Relevance and Applications of Rubber
6. Some Solved Examples
7. Summary

Natural rubber is an extremely elastic, resistant polymer, self-flowing from the latex of the Hevea brasiliensis tree, native to tropical regions. Although renewable and used for many years because of increased demand for the product, synthetic production has begun. Synthetic rubber comes from petrochemical feedstocks. It can be compounded into different kinds of rubbers for a wide variety of applications. Due to this versatility, synthetic rubber has come into very wide prominence in industries like automotive and consumer goods.

Understanding Natural and Synthetic Rubbers

Natural rubber is the polymer obtained from the latex sap of several species of plants in the genus Hevea; it is almost exclusively Hevea brasiliensis. This chemical offers excellent elasticity, resilience, and traction, hence its valorous applications in tires, footwear, medical supplies, and other related uses. Natural rubber is harvested by tapping trees for latex removal and further treating it into commercial sheets or blocks.

On the other hand, synthetic rubbers are produced through the petroleum by-product polymerization process in monomer form. This could produce various types of rubber for even more specialized applications. Synthetic rubbers can either replicate the qualities of natural rubber or be created with the finest properties, such as offering more resistance to heat or chemicals. The versatility of synthetic rubber has made it applicable to industries as wide-ranging as automotive and consumer goods, hence very fundamental in modern manufacturing.

It is a polymer that is capable of returning to its original length, shape, or size after being stretched or deformed. Rubber is a common example of an elastomer. The rubber obtained from natural sources is called natural rubber and polymers prepared in the laboratory which are similar to natural rubber are known as synthetic rubbers.

Natural rubber:

Natural rubber is a polymer that is obtained from rubber trees in the form of a milky sap known as latex. The latex is coagulated with acetic acid or formic acid. The coagulated mass is then squeezed. The raw natural rubber is a soft, gummy, and sticky mass. It is insoluble in water, dilute acids, and alkalies but soluble in benzene, chloroform, ether, petrol, and carbon disulfide. It absorbs a large amount of water. It has low elasticity and low tensile strength. It breaks when too much is stretched. Natural rubber is a hydrocarbon polymer. It has the composition$\left(\mathrm{C}_5 \mathrm{H}_8\right)_{\mathrm{n}}$ Destructive distillation of natural rubber gives mainly isoprene.

Isoprene

Vulcanization of rubber

Natural rubber is soft and sticky and therefore, in order to give strength and elasticity natural rubber is vulcanized. Vulcanization is a process of treating natural rubber with sulfur or some compounds of sulfur under heat to modify its properties, i.e., to render it non-plastic and to give greater elasticity and ductility. The sulphur reacts with the polymer molecules forming a cross-linked network. This cross-linking gives mechanical strength to the rubber. In addition, fillers, such as carbon black and zinc oxide are usually added to the crude rubber before vulcanization in order to improve its wearing characteristics.

Types of Synthetic Rubber

Synthetic rubber represents a family of materials with divergent properties and applications. Common ones include:

1. Styrene-Butadiene Rubber (SBR):

By far, this represents the largest tonnage of synthetic rubber in use. The primary uses are in tire manufacture. With good abrasion resistance and aging stability, SBR will undoubtedly find suitable applications in practically all automobile uses.

2. Butyl Rubber:

Due to its very high impermeability to gases, butyl rubber finds overwhelming application in the inner tubes of tires and any other device requiring airtight seals. The heat and aging resistance makes it very suitable for long-life products.

3. Neoprene:

The property of chemical stability of synthetic rubber, coupled with its oil resistance, gives neoprene a wide range of applications—from gaskets and seals to protective gloves.

4. EPDM (Ethylene Propylene Diene Monomer):

Since EPDM possesses very good weather resistance characteristics, it can be used in a great number of outdoor applications, such as roofing and auto weather seals.

These synthetic rubbers are tailored to the performance needs of various applications. In this way, manufacturers can come up with products that are strong, efficient, and relevant to the needs of the consumer. In many industries, these custom-made synthetic rubbers have brought innovation where natural rubber cannot.

Synthetic rubber is any vulcanisable rubber-like polymer, which is capable of getting stretched to twice its length. However, it returns to its original shape and size as soon as the external stretching force is released. Thus, synthetic rubbers are either homopolymers of 1, 3 - butadiene derivatives or copolymers of 1, 3 - butadiene or its derivatives with another unsaturated monomer. Neoprene, Thiokol, and buna-S are some of examples of synthetic rubber.

1. Neoprene:

It was the first synthetic rubber manufactured on a large scale. It is also called neoprene. Its monomer, chloroprene is prepared from acetylene. Chloroprene undergoes free radical polymerization to form neoprene. It polymerizes very rapidly and the reaction occurs by 1.4 addition of one chloroprene molecule to the other.

Many of the properties of neoprene are similar to natural rubber, but neoprene is more resistant to the action of oils, gasoline, and other hydrocarbons. It is also resistant to sunlight, oxygen, ozone and heat. It is non-inflammable. Thus, it is used for making automobile and refrigerator parts, insulation of electric wires and conveyor belts, etc.

2. Buna-S:

Buna-S rubber is a copolymer of three moles of butadiene and one mole of styrene. It is an elastomer.

Buna-S is generally compounded with carbon black and vulcanized with sulphur. It is extremely resistant to wear and tear and therefore, used in the manufacture of tyres and other mechanical rubber goods. It is obtained as a result of free radical co-polymerization of its monomers.

3. Buna-N:

It is obtained by co-polymerization of butadiene ad acrylonitrile.

It is very rigid and is very resistant to the action of petrol, lubricating oil and many organic solvents. It is mainly used for making fuel tanks.

Relevance and Applications of Rubber

Applications of both types of rubbers stretch way beyond simple ordinary products. In the automobile industry, the use of rubber in making tires is quite essential. Both types are used to adjust tires' performance, safety, and durability. For instance, natural rubber is commonly blended with synthetic rubber to attain optimum elasticity and grip of tires so as to strike a balance in performance versus durability.

In medicine, natural rubber finds its uses in the glove and catheter industries, as well as other medical devices, due to its biocompatibility properties and flexibility. The synthetic type of rubber, similar to latex alternatives, has a developing safe usage in allergic-sensitive populations so that safe work may be done by professionals working in the field of medicine.

Many other uses of rubber are used in the construction industry in seals, gaskets, and insulation materials. For instance, roofing membranes use EPDM since the material is UV and weather-resistant, hence it offers energy efficiency for building systems.

The academic coursework in rubber technology introduces students to a multidisciplinary view of materials science, chemistry, and engineering on how these materials are created and used. Research into sustainable methods for producing and recycling rubber is also becoming prominent as industries look toward lowering their impact on the environment and use of fossil fuels.

Case studies, such as that dealing with the development of eco-friendly tires using sustainable sources for their rubber, will illustrate innovations in this domain. It is about improving the performance of the product while careening a more sustainable course into the future; such developments underline the role of rubber in both industry and environmental stewardship.

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Some Solved Examples

Example 1:
What is true about natural rubber?

a) linear polymer
b) polymer of 2 methyl-1,3-butadiene
c) held together by strong intermolecular bonding
d) coiled structure

Solution:
Natural rubber is a linear polymer of isoprene (2-methyl-1,3-butadiene), also called cis-1,4-polyisoprene. The cis-polyisoprene molecule consists of various chains held together by weak van der Waals interactions and has a coiled structure. Thus, it can be stretched like a spring and exhibits elastic properties.

The correct answer is a, b, d.

Example 2:
Which element plays the role of a cross-linking agent in vulcanized rubber?

1) $C$
2) H
3) S
4) 0

Solution:
Vulcanization of Rubber is the treatment of natural rubber with sulfur under heat. Sulphur forms cross-links and thus rubber gets stiffened.

S plays the role of a cross-linking agent in vulcanized rubber.

Therefore, the correct answer is 3.

Example 3:
The structure of Neoprene is:

1)
2)
3)
4)

Solution:
The structure of Neoprene is:

3

Example 4:
Given below are two statements, one is Assertion (A) and the other is Reason (R).

Assertion (A): Natural rubber is a linear polymer of isoprene called cis-polyisoprene with elastic properties.

Reason (R): The cis-polyisoprene molecules consist of various chains held together by strong polar interactions with a coiled structure.

In light of the above statement, choose the correct one from the options given below:

1) Both (A) and (R) are true, and (R) is the correct explanation of (A).
2) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
3) (A) is true, but (R) is false.
4) (A) is false, but (R) is true.

Solution:
The assertion is correct, but Reason says that cis-polyisoprene molecules consist of various chains held together by strong polar interactions with a coiled structure, which is incorrect.

The chains are held together by weak van der Waals interactions.

Hence, the correct answer is 3.

Summary

Natural and synthetic rubber find applications in various industries. On one side, the natural one is derived from trees that have a number of special properties - elasticity and resilience. On the other hand, synthetic rubber is justifiably produced by chemical methods and is very versatile with all sorts of creation possibilities. The different forms of synthetic rubber include SBR, butyl rubber, neoprene, and EPDM. All of these offer special needs in manufacturing, the automobile industry, and the medical sector.