Class 8 Chemistry
Chapter 3: Synthetic Fibres and Plastics
1. Define Fibre?
Fibre is a strong and flexible thread like material that is used to make fabric. It is used to make ropes and nets and several household items.
2.What are the two types of Fibres?
- a) Natural Fibres
- b) Synthetic Fibres
Natural fibres are of two types
- Plant fibres
- Animal Fibres
3. What is a Monomer?
- Synthetic fibre is a chain of smaller units that are joined together. Each small unit is a chemical substance called Monomer.
4. What is a Polymer ?
- Many Monomers join together to form a large single unit called Polymer.
- “Polymer” in Greek, “Poly” means many “mer” means repeating units
- A polymer is a very large unit formed by the combination of a large number of small molecules (monomer) joined end to end by chemical bonds.
5.Define Polymerisation?
- It is process of joining together a large number of smaller molecules (monomer) to form a very large molecule (polymer)
- Ex: Cotton fibre us polymer made up of cellulose. It is made up of many glucose monomer.
- Ex: Nylon is prepared by polymerisation molecule of amide molecules.
- Amide molecule – Monomer
- Nylon – Polymer
6. Types of polymers:
- Linear polymer – Polymer in which monomers are linked in linear arrangement is known as linear polymers.
- Cross linked polymers – Polymers in which monomers are cross linked to each other are known as Cross linked polymers.
- Synthetic fibres are also called as Human made fibres.
- Ex: Nylon, Rayon, polyester, acrylic fibre.
7. How Rayon is prepared?
- It is a synthetic fibre prepared from wood pulp.
- It is also called as artificial Silk.
- It is cheaper than silk and can be dyed easily.
- Wood pulp is dissolved in alkaline solution and then passed through tiny pores to convert them into fibres
- They are then passed through sulphuric acid to make them hard. These are spun into yarn and then woven into fabric.
- Rayon is also called as Regenerated fabric because it is reformed from original cellulose fibres.
8. Uses of Rayon:
- Rayon absorbs sweat and hence can be worn in summer.
- Rayon mixed with cotton to make bedsheets, dresses, aprons, caps.
- Rayon with wool to make beautiful durable carpets.
- Rayon is used to manufacture tyre cords.
- Rayon is used to make bandages, lint for surgical dressing of wounds.
What is Nylon??
- Nylon is derived from New York and London.
- From these two cities they are simultaneously developed and marketed.
- Nylon – the polymer it is made from / prepared by the polymerisation of large number of amide molecules.
- Nylon is very strong, lustrous, highly elastic, lightweight, easy to wash, wrinkle free
- It does not observe water and not attacked by fungi, moths etc.
- It remains insoluble in most of the common solvents.
Uses of Nylon:
- Nylon is used to make parts of the washer pullers etc.
- Well with nylon is used to make socks, suits, carpets.
- Nylon is used in the production of saree, shirts, necktie, socks etc.
- Nylon has high tensile strength used to make fishing net, climbing rope, string, bristles for a toothbrush, paint brushes.
What is Polyester??
- Polyester is the polymer made up of Ester.
- Ex: Terylene, Terene, Dacron.
- Polisted as light, strong, elastic, observes little amount of water, dries quickly and wrinkle free.
Uses of Polyester:
- It is used for making the conveyor belt.
- It is used for making sail for sail boats.
- Terrywool is used for making suits.
- Terrycot is used to make shirts, trousers other dress materials.
- Polyester fibres (Terylene) is used for the manufacturing saree, dress material, curtains etc.
Note: PET – Polythene Teraphthalate. It is used to make flims, utensils and wires.
Bottles made using PET used in industries for selling oil soft drinks etc.
Acrylic fibre:
- Acrylic fibre is a synthetic fibre made from Poly acrylonitrile. It is obtained by polymerisation of large number of monomers.( Acrylonitrile molecules)
- It is light weight, soft warm, wool like feel.
- It can be dyed with different colours.
- Uses of acrylic fibres:
- It is used to make sweater, shawls, blankets, jackets, cushions etc.
Difference between Natural fibres and Synthetic fibres:
Natural Fibres | Synthetic Fibres |
Fibres obtained from both the plants and animals. | Synthetic fibres obtained through different chemical processes in the industries. |
Plants cotton fibre jute fibre. Animals – wool, silk. | Raw materials used in petrochemicals. Ex: Rayon, Nylon etc…, |
They have low tensile strength. | They have high tensile strength |
They observe more moisture and hence comfortable to wear in summer. | They absorb very little water and hence not comfortable to wear in summer. |
They are non elastic and wrinkled. | They are elastic, flexible and wrinkle free. |
Since they are not obtained from plant/animal fibres they are attacked by Moths, moulds. | They are not attacked by moths /moulds. |
They are biodegradable. | They are not biodegradable and hence causes soil pollution. |
They do not catch fire and hence advised to wear cotton clothes while cooking, bursting crackers. | They catch fire easily and not advised to wear during cooking, bursting crackers. |
They are made from natural fibres | They are chemically inert. |
They are very safe | It causes eczema, skin disease in some people. |
PLASTICS
1.Plastics are polymers made up of very large no. of small monomers joined end to end to form long chains.
2. They are usually carbon compounds.
3. Plastics is a synthetic material that on heating becomes soft and moulded into desired shape and then hardened to provide durable article. This is also referred to as Plasticity.
Ex: Polythene, Terylene, PVC (Polyvinyl Chloride)
LDPE – Low Density Polyethene is used to make Polyethene bags.
How Plastics are classified?
Based on their reaction to heat, Plastics are classified into Thermoplastics and Thermosetting Plastics.
Difference between Thermoplastics and Thermosetting Plastics?
Thermoplastics | Thermosetting Plastics |
Plastic that is repeatedly melted on heating and hardened on cooling into different shape is called Thermoplastics | Plastic that is once moulded into particular shape once then cannot be moulded second time. |
They become soft on heating | They do not become soft on heating |
They are comparatively less tough | They are more tough and rigid |
They are less resistant to high temperature | They are more resistant to high temperature |
They can be recycled | They cannot be recycled |
Ex: Polyethene, PVC | Ex: Bakelite, Melamine, Formica |
Properties and uses of Plastics:
- Plastics do not react with air and water. Ex: PVC is used to make water pipes, soles of shoes, rain coat, water tank etc.
- Plastics are very light. Ex: Thermocol it is very light but very rigid. It is used to make disposable cups, packaging material for Cell phone, TV, Fridge etc.
- Plastics are strong and durable. They can be moulded into different shape and articles. They are cheaper than metals. Ex: Melamine – Used to make unbreakable kitchenware, dinnerware, floor tiles etc.
- Polyethene – Used to make carry bags, cell tapes etc.
- PVC – Used to make floor tiles, durable toys, furniture, bottle.
- Plastics are poor conductors of heat. Ex: Bakelite used to make handles of utensils.
- Polystyrene is used to make Icebox. It is filled in hollow walls of refrigerators, air coolers etc.
- Plastics are poor conductors of electricity. Ex: Bakelite is used to make electrical switch and plugs. Ex: PVC is used as insulation cover in electrical wires.
- Plastics are inert to chemicals. Ex: Teflon is used to make non stick cookware.
- Plastics are insoluble in water. Ex: Containers, Buckets, Water tanks are made up of Plastics
- Plastics are low price
- Plastics are highly inflammable. They burn easily and produce harmful gases and pollute environment.
Difference between Biodegradable and Non Biodegradable substances?
Bio degradable substances | Non Biodegradable substances |
Substances that are easily breakdown by the action of bacteria are called Biodegradable substances | Substances that are not breakdown by the action of bacteria are called Non Biodegradable substances |
They produce harmless products to environment during breakdown | If they are heated for degradation, they release harmful substances |
Ex: Vegetable, fruit peels, cotton, wool, cloth etc. | Ex: Synthetic Fibres, Plastics |
Note: Bioplastics are produced nowadays using natural materials such as Cornstarch, Vegetable oil. Thet are biodegradable and eco friendly.
What are the environment hazards due to plastics?
- When plastics are burnt, they produce harmful substances and cause air pollution.
- When plastics are dumped into water, it cause water pollution.
- Plastics dumped into soil causes soil pollution. They cannot be degraded by the microorganisms. They prevent rainwater seeping (entering) the Earth. So water stagnant and form muddy pools.
- Polybags thrown in sewage are the main cause for clogging drains and sewage lines.
- Animals sometimes eat these polybags, it choke their respiratory system and block digestive tract leading to death.
- Chemicals used in the plastic manufacturing industries can cause cancer to workers who are working there.
- During recycling of thermoplastics, they add colouring agents. Foods should not be stored in recycled plastics.
Solutions:
- Follow 5R Principle – Refuse, Reduce, Reuse, Recycle, Recover
- Take cotton bags/ Jute bags during shopping. Don’t ask for polybags
- We should use clean, dry plastic bags, containers, plastic disposable bottles for reuse
- Do not throw plastic disposable bottles, polybags,wrappers on road
- Never use articles made up of plastics in sewage system.
- Use separate bins for collecting waste.
- Green Bin – Biodegradable waste such as vegetable peels, food, paper can be thrown here.
- Blue Bin – Throw in non biodegradable waste and glass. These can be melted and reused.
Useful links: