3. Synthetic Fibers and Plastics
This chapter talks about types of synthetic fibres & plastics, their properties and uses.
A fibre is a single and elongated piece of a given material similar to threads. They are a chain of small
units of that material joined together. Fibres are used to make fabrics and other household articles.
Fibres are of two types
1. Natural Fibres
2. Synthetic Fibres
Polymers – “Poly” means many & “mer” means part/unit. When many small units combine to form a
large single unit, the chain is called a “Polymer”. Polymers occur in natural as well as synthetic fibres.
3.1
Natural Fibres
Natural fibres are obtained from plants or animals. For example
1.
2.
3.
4.
Cotton
Wool
Silk
Jute
Cotton is a soft and fluffy natural fibre that grows around the seeds of the cotton plant. It is made up of
cellulose. Cellulose is made up of a large no. of glucose units
Wool is an animal product and is obtained by shearing the sheep of its hair. Wool is made up of protein
units
Silk is a natural protein fibre, which can be woven into textiles. It is obtained from the cocoons of the
larvae of the mulberry silkworms
Jute is a soft and shiny plant fibre which can be spun into coarse threads and used for making sacks. It is
composed of cellulose (build blocks of plant fibre) and lignin (building blocks of wood fibre). The jute
fibre comes from the stem and outer skin of the jute plant
3.2
Synthetic Fibres
Synthetic fibre is a chain of small units joined together in which each unit is actually a chemical substance
that is produced synthetically (artificially), usually from petroleum products.
3.2.1
Fibres
The following are the different types of Synthetic Fibres
1. Rayon – It is also called as Artificial Silk. It is obtained from wood pulp, but it is still considered
to be a synthetic fibre. It is cheaper than silk and can be woven like silk fibres. It can also be dyed
in a wide variety of colours.
2. Nylon – It was the first fully synthetic fibre prepared from coal, water & air in 1931. Nylon is
strong, elastic & light. Actually, nylon fibre is even stronger than a steel wire. Because of these
properties nylon is used to make parachutes & ropes for rock climbing as it can sustain the weight
of a human body also.
3. Polyester – As the names suggests it is composed of repeating (poly) units of esters. Ester is a type
of chemical, which consists of an Acid + Alcohol molecule combination. Interestingly, esters are
the chemicals which give fruits their smell. It is wrinkle-free, remains crisp & is easy to wash.
Terylene is a type of polyester, which is popular for making dress materials. PET is also a type of
polyester and is used for making products like water bottles, films etc.
4. Acrylic – This synthetic fibre resembles wool. Acrylic is less expensive than wool, is durable & is
available in wide variety of colours.
The following are the characteristics/ advantages of Synthetic Fibres
1.
2.
3.
4.
5.
Durable
Less expensive
Absorb less water
Readily available
Easy to maintain
The main disadvantage of synthetic fibres is that if they get burnt, they melt & stick to the body of the
person wearing it. So, we should never wear clothes made of synthetic fabrics while working in the
kitchen or in a laboratory.
There are some fabrics which are made by mixing two types of fibres. For example
1. Polycot (Polyester + Cotton)
2. Polywool (Polyester + Wool)
3. Terrycot (Terylene + Cotton)
Such fabrics exhibit the properties of both the fibres and are generally cheaper and better than the fabrics
of individual fibres
3.2.2
Plastics
Plastics are also polymers just like synthetic fibres. Some plastics have a linear arrangement of constituent
units while others have a cross-linked structure
The following are the characteristics/advantages of Plastics
1.
2.
3.
4.
5.
Light, strong & durable
Non-reactive – It does not corrode as it does not react with water & air
Easily mouldable into various shapes/objects
Can be recycled and reused
Cheaper than metals therefore plastic goods are cost effective as compared to equivalent metallic
goods. For example – buckets, bins etc
6. Poor conductors of heat & electricity so they are used as covering for electrical wires and as
handles for screw drivers.
Plastics can be classified into following categories based on their thermal properties
1. Thermoplastics
2. Thermosetting Plastics
The following is the difference between thermoplastics & thermosetting plastics
Thermal
characteristics
Uses
Thermoplastics
They are not heat resistant and
get deformed easily on heating
Used in the manufacturing of
toys, combs, containers etc
Thermosetting Plastics
Once moulded, they cannot be
softened on heating
Used in the manufacturing
of electrical switches, handles
of utensils etc
Examples
1.
Polythene
3.
Bakelite
2.
PVC
4.
Melamine
5.
Teflon
Some interesting uses of Plastics
1. Teflon is used for coating the inside of non stick cookware. It has high melting point and can be
used safely. The food does not stick to this material; therefore we need to add less oil for food
preparation
2. Microwave cooking requires special plastics, which do not melt during cooking
3. Uniforms of fireman are coated with melamine, thus making it flame resistant
3.3
Plastics & the Environment
The materials that are decomposed through natural processes such as action by bacteria are called
Biodegradable Materials. Vegetable waste, paper, cotton clothes, wood & woollen clothes are
biodegradable.
The materials which are not easily decomposed by natural processes are called non-Biodegradable
materials. For example – Tin, aluminium, metal coins & plastic bags are non-biodegradable
The following are the disadvantages of using non-biodegradable materials such as plastics
1. They are not environment friendly. Once they are created, they cannot be destroyed naturally and
the disposal of garbage containing such material becomes difficult
2. Animals eating garbage from the garbage dump swallow polythene bags & food wrappers. The
plasters choke their respiration system & this may lead to their death
3. Polythene bags thrown here & there, clog the sewers and drains creating sanitation problems