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Man made artificial
materials are present everywhere and are an important part in our everyday
lives. Plastic, nylons, polyesters, soaps and detergents, rubber are some
of the materials, which we can name. In
this chapter we will discuss man made materials that are based on organic
chemistry. The entire man made organic materials industry depends on the
process of polymerization. Small monomer molecules are reacted to form large
chain polymers. Attaching various functional groups to the side chains can
vary the properties of the polymers.
What
we will study in this chapter
1.
Artificial fibers
2.
Plastics
3.
Artificial rubber
4.
Soaps and detergents
Artificial
fibers
Natural fibers such as
wool and silk show that they are made of components called polymers.
Scientists are even looking at spider’s web to determine how to make fine
threads with strength. The starting material for polymers can be natural
material such as wood pulp or by products of crude oil distillations.
Rayon
Rayon is made from
cellulose obtained from wood pulp. Cellulose
is a naturally occurring polymer. Threads made from rayon have silk like
appearance and therefore it is called artificial silk.
Preparation
of rayon
The starting material for
rayon is the cellulose in the wood pulp. The following raw materials are
needed for the manufacture of rayon : |
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The first step in the
manufacture of rayon is to make viscose. Viscose is a syrup like liquid
which forms when cellulose is treated with NaOH and CS2. Viscose
is a thick viscous liquid. The reaction is shown below.
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The viscose is made to
pass through a cylindrical drum, which has fine holes on it. The viscose is forced through these holes as a fine jet. The cylinder is called a
spinneret. The threads formed are collected in a dilute sulphuric acid
medium. Since the viscose solution has NaOH, it is slightly alkaline in
nature. By treating the viscose fibers in dilute sulphuric acid, the fibers
are neutralized. The fine threads are called viscose rayon or just rayon.
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Rayon thread is fine and
silk like in nature and shines like silk. Rayon is sometimes known as a
regenerated fiber because in its process the cellulose is regenerated in
another form.
| Uses
of rayon |
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Rayon is used in
garment and textile industries. Some saree and shirt materials are made
from rayon.
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Rayon is used in the
tyre industry for making cords used in tyres.
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Rayon mixed with wool
and other fibers is used in carpet industry.
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Rayon is used in
medical and pharmaceutical industry for making bandages, bottles, bags,
etc.
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Nylon
Nylon was discovered in
1935 and is a polymer which has repeated functional group of an amide. An
amide unit is ---CO---NH---. This is the reason why nylon is called a
polyamide. The name nylon is derived from two cities where it was discovered
namely New York (ny) and London (lon).
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Preparation
of nylon
Nylon is made from
dicarboxylic acid called adipic acid. Adipic acid is actually tetra
methylene dicarboxylic acid. A
diamine called hexamethylene diamine is added to adipic acid.
| The raw materials
required for the manufacture of nylon are : |
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Polymerization takes
place and water along with a polyamide that is nylon is the end product.
The reaction is shown below.
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The COOH or the carboxyl
groups from the acid react with the NH2 or the amino group from
the diamine to form an amide structure, which is a polymer. The number
“n” shows that there are very large numbers of ---CO---NH---- groups.
This is an amide structure hence the product is called a polyamide. The
polyamide is forced through spinnerets to get threads of nylon. The
polyamide can also be cast into different shapes by moulds.
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Properties
of nylon
1.
Strength : nylon fibers are strong as they are long chain polymers.
Nylon ropes can handle heavy loads wherever applicable, as they do not break
easily.
2.
Elasticity : Nylon fibers are very elastic. This means that they regain
their original shape once the load on them is released. This is the reason
why socks and stockings are made out of nylon. They do not loose their shape
even after repeated use.
3.
Water absorption : Nylon absorbs very little water or moisture. This
is the reason why nylon clothes or shirts are called “drip-dry”.
4.
Wrinkle resistant : Since the elastic properties of nylon are very
good, fibers made of nylon do not wrinkle easily. If wrinkled and released,
they get back to their original shape quickly.
5.
Abrasion resistant : Nylon fibers withstand wear and tear or abrasion
much better. The basic polyamide from which it is made is long chained and
completely unreactive to external handling. Thus clothes made from nylon are
long lasting.
In addition to these properties, nylon is also moth resistant and light in
weight. The fibers drawn from a spinneret can be made very fine and thin,
thus the texture of nylon can be very fine and smooth. Nylon is also
chemically more inert than the natural fibers and is insoluble in most
common solvents.
| Uses
of nylon |
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Nylon threads, due to
their high strength and elasticity are used to make tyre cords, fishing
nets, climbing ropes, strings in badminton or tennis racquets, etc.
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Nylon is used for
manufacturing fabrics such as shirts, sarees, socks, etc. The clothes
are durable, they can dry quickly, and they last longer.
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Nylon mixed or
blended with wool or rayon has use in making suit materials, carpets,
etc.
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Nylon
is molded into making many industrial machine parts such as core for a
transformer-winding, etc.
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