Lesson: Synthetic Fibres and
Plastics
Topic 1: Synthetic Fibres
Polyester fibre is used to make dress material. Why?
Polyester is a synthetic fibre which remains wrinkle free and is easy to wash. It is light, durable and takes less time to dry. So, it is quite suitable for making dresses and other clothes.
Define natural fibres.
Fibres obtained from plants and animals are known as natural fibres.
What are synthetic fibres?
Synthetic fibres are man-made fibres. They are made by the chemical processing of petrochemicals.
How is rayon synthesised?
Rayon is manufactured from purified cellulose, primarily from wood pulp, which is chemically converted into a soluble compound. It is then dissolved and forced through a spinneret to produce filaments which are chemically solidified, resulting in synthetic fibres of nearly pure cellulose. Therefore, rayon is manufactured from naturally occurring polymers and is therefore considered a semi-synthetic fibre.
Name the raw materials used in the manufacture of nylon.
Coal, water and air are used in the manufacture of nylon.
Name two common forms of polyester.
Terylene and Terrycot
Which synthetic fibre is a cheap substitute of silk?
Rayon is a cheap substitute of silk.
List three things made of polyester.
Three things made of polyester are:
Name four articles made of nylon.
Socks, ropes, tents and toothbrushes are made of nylon.
Name two things that can be made from rayon.
Rayon is mixed with cotton to make bed sheets and mixed with wool to make carpets.
Why is nylon popular for making clothes?
Nylon is strong, elastic and light. It is also lustrous and easy to wash. So, it has become popular for making clothes.
What is acrylic? Give its uses.
Acrylic is a synthetic fibre which resembles wool. It is durable and inexpensive and can be easily dyed. It is used to make sweaters, blankets, shawls and other thermal wear.
Why is acrylic considered a substitute of wool?
Acrylic is lightweight, soft and warm with wool-like feel. It is readily available in a variety of colours. The wool obtained from natural sources is quite expensive whereas acrylic fibre is relatively cheaper. It is also strong and more durable than wool. Due to these properties, acrylic is considered as a substitute of wool.
Aman took with him some nylon ropes, when he was going rock-climbing. Why would he choose nylon ropes instead of ropes made of cotton or jute?
Nylon rope is more durable, elastic, strong and does not break easily as compared to ropes made of cotton or jute. This is the reason why nylon ropes are used in rock climbing.
Tina is learning how to cook. Why has her mother told her not to wear nylon clothes while working in the kitchen?
Nylon is a synthetic fibre. It catches fire easily and melts on heating. The melted fabric sticks to the body of a person wearing it, which is dangerous. This is why Tina’s mother has warned her against wearing nylon clothes while working in the kitchen.
Why are synthetic fibres more popular than natural fibres for making clothes?
The following properties make the synthetic fibres more popular than natural ones for making clothes:
How strong is nylon?
Nylon has the advantages of being strong, elastic and light. A nylon thread is stronger than a steel wire of the same thickness and can support more weight. It is used to make parachutes and ropes for rock-climbing.
List the disadvantages of synthetic fibres.
Disadvantages of synthetic fibres are:
Sam is going to Chennai to spend his summer vacations and he needs to buy some shirts for him. Can you suggest whether he should buy cotton shirts or shirts made from synthetic material? Give reason for your answer.
Sam should buy cotton shirts for summer. Synthetic shirts will be uncomfortable as they do not have sufficient pores for the sweat to come out, evaporate and cool the body whereas the large pores of cotton shirts allow the body sweat to come out through them, evaporate and make the person wearing it feel cool and comfortable.
Write a note on rayon.
Silk has a beautiful texture. Because it is expensive to produce, people began to look for ways to produce silk artificially. Towards the end of the nineteenth century, scientists succeeded in creating a fibre by chemical treatment of wood pulp. The fibre had similar properties as silk. The scientists called the fibre rayon or artificial silk. Rayon is cheaper than silk but can be woven like silk fibres. It can be mixed with cotton to make bed sheets and with wool to make carpets.
Explain how manufacturing synthetic fibres actually helps conserve forests.
Synthetic fibres are made of petrochemicals. Their manufacture does not depend upon plants and trees. Forests are not destroyed to manufacture synthetic clothes and other items. So, indirectly manufacturing synthetic fibres actually helps in the conservation of forests.
A nylon fibre is stronger than steel of the same thickness. Can nylon be used to build bridges?
Nylon fibres are stronger than steel fibres of the same thickness. But steel is much harder than nylon. Steel cannot be cut easily and does not melt easily. Bridges need to be made of materials which are hard and strong and can withstand weight. Although nylon is strong and can withstand weight, it is not hard. Being a synthetic fibre, nylon melts when heated and can be cut easily, too. Therefore, nylon cannot be used to build bridges.
Topic 2: Plastics
Name two types of plastic.
Thermosetting plastic and thermoplastic
Name two thermosetting plastics.
Bakelite and Melamine.
Plastic objects are available in all possible shapes and sizes. How?
Plastic is very light, strong, durable and can be moulded into different shapes and sizes. That is why plastic objects are available in all possible shapes and sizes.
Why are some plastic bottles commonly used to store chemicals?
Since plastic is non-reactive, it does not get corroded easily by diluted acids and alkalis. Therefore, some plastic bottles are commonly used to store mild chemicals.
Why does a bucket made of plastic not corrode like a bucket made of iron?
Metals like iron rust when exposed to moisture and air. But plastic does not react with either water or air and does not corrode easily. That is why a bucket made of plastic does not corrode like a bucket made of iron.
Why is melamine used to make kitchenware?
Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics. Therefore, it is used to make kitchenware.
Should you use a plastic bag or a jute bag for shopping?
Plastic takes several years to decompose, so it is not environment-friendly. It burns slowly and does not easily get completely burnt. During burning, it releases poisonous gases, causing air pollution. Therefore, you should use jute bags instead of plastic bags.
Why should you not throw plastic materials on the road?
Plastic is non-biodegradable. When thrown on the road, it can enter the drainage system, causing clogging of drains. Therefore, we should not throw plastic bottles on the road.
Explain why thermoplastics are recyclable whereas thermosetting plastics are not.
Since thermoplastics can be softened easily on heating again and again and can be moulded into any desired shape, they are recyclable. On the other hand, thermosetting plastics cannot be re-softened on heating and moulded. Due to this reason, thermosetting plastics are non-recyclable.
Differentiate between thermoplastics and thermosetting plastics. Give two examples of each.
Thermoplastics: Plastics which get deformed easily on heating and can be re-moulded repeatedly without undergoing any chemical changes are called thermoplastics. Polythene and PVC are examples of thermoplastics.
Thermosetting plastics: Plastics which can be moulded only once and after solidification cannot be softened on heating are called thermosetting plastics. Bakelite and melamine are examples of thermosetting plastics.
Should the handle and bristles of a toothbrush be made of the same material?
Handle and bristles of a toothbrush should not be made of the same material because the handle of a toothbrush has to be hard and rigid whereas the bristles of a toothbrush have to be soft and flexible. This means that the handle of a toothbrush should be made of a thermosetting plastic which is a hard material and its bristles should be made of a thermoplastic which is a soft material.
Differentiate between biodegradable and non-biodegradable substances.
A substance which gets decomposed naturally by bacterial action is called biodegradable. For example, dead animals and human excreta are decomposed into simpler compounds by bacteria.
A substance which does not decompose naturally into simpler compounds by bacterial action is called non-biodegradable. For example, plastic bags and aluminium cans are non-biodegradable.
State whether the following statements are true or false. Justify each answer.
a) Plastics should be recycled, and it is safe to store food in recycled plastic containers.
b) Due to their non-reactive nature, some plastic containers are used in the chemistry laboratory to store concentrated acids.
c) You should not throw plastic wrappers or plastic bottles on beaches as doing so harms the ecosystem.
a. False. Plastics should be recycled. However, during recycling, some colouring agents are added, which are harmful if consumed. So recycled plastic containers should not be used to store food.
b. False. Plastic containers are non-reactive, and mild chemicals can be stored in them. However, concentrated acids are highly corrosive and can melt plastic. So, they are stored in glass containers.
c. True. Plastic wrappers are non-biodegradable and can cut off air from animals living underground or aquatic animals and plants. If they cannot breathe because the surface is clogged with plastic wrappers, they eventually perish. They can also choke animals who swallow them.
List and explain three important properties of plastic.
Three important properties of plastic are:
i. Plastic is non-reactive. Plastic does not react with water and air. It does not get corroded easily. Therefore, plastic containers are used to store various kinds of materials.
ii. Plastic is light, strong and durable. Plastic can be moulded into various shapes and sizes. It is generally cheaper than metal; therefore, it is widely used in industries and for making household articles.
iii. Plastic is a poor conductor of heat and electricity. Electric wires have plastic coverings, and handles of screwdrivers and cookware are also made of plastic.
What are the advantages of using a plastic container?
Due to their light weight, low price, strength, durability and ease of handling, plastic containers are used to store food items, water, milk, pickles, dry food, medicines and mild chemicals. Metals like iron get rusted when exposed to moisture and air. But plastic does not react with water and air and so does not get corroded easily. Therefore, plastic containers are used to store various kinds of materials, including many mild chemicals. After their use or breakage, they can be sold as scrap and be recycled.
Plastic is used for making a large variety of attractive objects of our daily use. But it is advised to minimise usage of plastic. Why?
Since plastic is non-biodegradable, it is not environment-friendly. Plastics on burning release poisonous gases causing air pollution. When thrown in water bodies, it causes water clogging and harms aquatic life. If animals consume plastic, it chokes their respiratory system causing death. Therefore, it is advised to be careful with plastic use.
Why are the following made of thermosetting plastics?
a) Saucepan handles
b) Electrical plugs and switches
a) Saucepan handles: Saucepan handles are made of bakelite, a thermosetting plastic. Since bakelite is hard and a bad conductor of heat, the handles retain their shape and can be held by us, even if the saucepan is very hot.
b) Electrical plugs and switches: These are also made of bakelite, which is a poor conductor of electricity and can tolerate heat better than other plastics. Hence, it prevents possible fire in electrical installations due to over-heating. It also protects you from electric shocks. In addition, it does not get deformed or get softened due to over-heating.
Suggest some ways to limit the consumption of plastics.
Ways to limit the consumption of plastics are as follows:
List three advantages of using plastic containers to store food.
Advantages of using plastic containers to store food:
a) Do not react with food, air or water
b) Are strong and light
c) Come in various sizes, shapes and colours