Synthetic fibres and plastics class 8 notes

Fabrics are used to make our daily wear clothes. Fabrics are made of fibres obtained from both natural and artificial sources. Some examples of natural fibres include wool, cotton and silk. Polyesters and terylene are some synthetic fibres. Synthetic fibres are cheaper than natural fibres. Plastic is a polymer that can be reused and recycled. Plastics are classified as thermoplastics and thermosetting plastics. Class 8 Science Chapter 3 Notes on Synthetic Fibres And Plastics are given in the article.

Key Terms: Synthetic fibres, rayon, nylon, polyester, acrylic, silk, natural fibres, polymers, plastics

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Fibre

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Fabrics which are used to form the clothes we wear are made from fibres.

• Fibres can be obtained from natural and artificial sources.
• They are also used to make a lot of household items.

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Natural Fibre

The fibres that occur naturally are known as natural fibres. Humans derive these from plants or animals. For eg: cotton, wool, silk, etc.

Silk

The silk fibre is obtained from the cocoon of a silkworm. 10 kg of the cocoon material is used to create 1 kg of silk.

• Due to the quality of the material and its production process, silk is expensive. 
• It is used to make ties, sarees, etc.

Silk

Read More: NCERT Solutions Class 8 Science Chapter 3 Synthetic Fibres and Plastics

Synthetic Fibre

The fibres that are created by humans artificially are known as synthetic or man-made fibres. For eg: rayon, nylon etc.

Rayon

Rayon is formed of purified cellulose that is chemically converted into a soluble compound.

• Rayon is derived from natural sources such as wood pulp.
• It is highly absorbable, comfortable and soft.
• However, it is considered a man-made fibre as it is treated chemically.
• It is also mixed with cotton to make curtains and bedsheets.
• It is inexpensive as compared to silk though it can be woven like silk fibres.

Read More: Uses of Rayon

Nylon

Nylon is a synthetic fibre that is obtained from water, coal, and air.

• It was the first fully synthetic fibre that was obtained.
• The properties of nylon are that it is light, strong, and elastic.
• Nylon is used in the manufacturing of socks, tents, ropes, curtains, car seat belts, sleeping bags, etc.

Nylon is also used to make ropes for rock climbing and parachutes.

This is done because a nylon thread is stronger than a steel wire.

Polyester

Polyester is formed of repeating units of a chemical known as an ester.

• Polyester is a crease-free synthetic fibre.
• It is used to make dress materials as it is crisp and easy to wash.
• A popular polyester is known as Terylene.
• Polyester is used to make hoses, nets, ropes, raincoats, clothing and medical textiles.

Acrylic Fibre

Acrylic is a synthetic fibre that is similar to wool.

• The wool that is obtained from natural sources is quite expensive.
• However, clothes that are formed of acrylic are relatively cheap.
• Synthetic fibres are durable and affordable and hence are more popular than natural fibres.
• They are durable as they retain their shape and are warm to wear.
• It dries quickly and is easy to wash. 
• Domestically, it is used to make furniture, blankets, sweaters and socks while industrially it is used to form vehicle covers, luggage, craft yarns, etc.

Synthetic fibres are more affordable and durable than natural fibres. However, they too have certain disadvantages. 

• Synthetic fibres melt when they are heated. 
• If the clothes made of synthetic fibres catch fire, it can be disastrous as the fabric melts and then sticks to the body of the person. 
• Therefore, synthetic clothes should not be worn while working in the kitchen or a laboratory.

Polymer

The word ‘polymer’ is a combination of two Greek words - poly meaning many and mer meaning part or unit. A polymer is a substance that is formed of repeated similar subunits.

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Plastic

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Plastic is a polymer-like synthetic fibre.

• All plastics don’t have the same arrangement of units. In some, the units are linear while in others, it is cross-linked.
• Plastic has a variety of uses as it can be reused, recycled, coloured, melted, rolled into sheets, and even made into wires. 

Plastic

Types of Plastics

The two common types of plastics - thermoplastics and thermosetting plastics are as follows –

Thermoplastics

Plastic that is easily deformed on heating and is easily bent is called thermoplastics. Eg: PVC and polyethene. Thermoplastics are used to manufacture toys, combs and different containers.

Thermosetting Plastics

Plastics that once moulded can not be softened through heating are known as thermosetting plastics. Eg: melamine and bakelite.

• Bakelite is a poor conductor of electricity and heat. It is therefore used to make handles for utensils and electrical switches.
• Melamine resists fire and can tolerate heating better as compared to plastics. It is hence used to make floor tiles, kitchenware and fabrics that resist fire.

Characteristics of Plastics

Plastics have the following characteristics - 

– They are non-reactive. Plastics do not react with water or air and are not corroded easily. 

– Plastic is strong, light, and durable. They can be moulded in various shapes and sizes. 

– Plastic is a poor conductor of heat and electricity. Therefore, electric wires have a covering made of plastic. Plastic is also used to make the handles of frying pans.

While storing food items, milk, pickles, water, dry food, etc., plastic containers are the most convenient. Why is it so?

This is because plastic containers are light in weight, have a lower price, have good strength and are easy to handle. 

As they are lighter compared to metals, they are also used in cars, aircraft and spacecraft.

Environmental Effects on Plastic

Plastic is not environmentally friendly as it takes several years to decompose. Plastic, therefore, causes pollution.

• The burning process of plastic is quite slow and it does not get completely burnt easily.
• It releases lots of poisonous fumes that contribute to air pollution in the process.

Some of the environmentally friendly habits that can be followed are –

Implement the 4 R principle in everyday life. Following are the 4Rs:

• Reuse
• Reduce
• Recycle
• Recover

Environmental Effects on Plastic

Uses of Plastics

• Plastics are extensively used in the healthcare industry for the packaging of tablets, syringes, doctors’ gloves and many medical instruments.
• Special plastic cookware is used in microwave ovens to cook food. In microwave ovens, the heat cooks the food but does not affect the plastic vessel.
• Teflon is a special plastic on which water and oil do not stick. It is used for nonstick coating.
• Though synthetic fibre catches fire easily, the uniforms of firemen have a coating of melamine plastic in order to make them flame resistant.

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Biodegradable and Non-Biodegradable Materials

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Biodegradable material is a material that decomposes through a natural process. For example paper and fruits.

Materials that are not easily decomposed through natural processes are non-biodegradable. For example tin and plastic.

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Things to Remember

• Fabrics that make our clothes are formed from fibres obtained naturally or artificially.
• A polymer is formed of many repeating units.
• Fibre that is obtained chemically by treating wood pulp is known as rayon or artificial silk.
• Nylon is a synthetic fibre that is formed from water, air, and coal.
• Acrylic is a warm-to-wear synthetic polymer of methyl methacrylate.
• Plastics can be broadly classified into two categories - thermosetting and thermoplastics.

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