These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 13 Notes – Synthetic Fibres and Plastics act as excellent revision resources, particularly in preparation for board exams.
Synthetic Fibres and Plastics Class 8 DAV Notes
→ Natural Fibres: Fibres which are obtained from either plants or animals are called natural fibres, e.g. cotton, jute, wool, silk, etc.
→ Synthetic Fibres: Fibres which are made in laboratories and factories are called synthetic fibres or man-made fibres or artificial fibres, e.g. nylon, rayon, etc.
A fibre is composed of simple molecules which are joined to form a long chain. These simple molecules are called monomers. The long chain of monomers is called a polymer. Synthetic fibre is also a chain of small units (monomers) joined together.
→ Polymerization: The process by which artificial fibres are made from simple molecules is called polymerization.
→ Rayon: Rayon is also known as artificial silk because its properties are similar to natural silk. Rayon is made from cellulose which comes from plants. Due to this, rayon is not considered as truly artificial fibre.
→ Uses of Rayon:
- It is mixed with cotton to make bed sheets. It is mixed with wool to make carpets.
- Rayon can be easily dyed in a wide range of colours.
- It is used in making apparels, e.g. dresses, jackets, linings, suits, hats, etc.
- It is used in making many industrial products; like surgical products and tyre cords.
→ Nylon: Nylon is truly artificial fibre because it does not use any natural fibre as its raw material.
→ Uses of Nylon:
- Nylon is highly elastic, tensile and has silk-like appearance. Due to this, it is used in carpets and socks.
- Nylon is used in many military applications; like ropes, parachutes, etc.
- It is highly durable and hence is used in making seat belts, tyre cords, clothes, etc.
- It is used for making many household items; like toothbrushes, combs, hooks, etc.
- It is used for making ropes for rock climbing and fishing nets.
→ Terylene: Terylene is used for making clothes. It is elastic, highly durable, wrinkle resistant and moth resistant.
→ Uses of Terylene:
- It is used for making fabrics; like shirts, trousers and other dress materials.
- It is used for making sails for boats.
- It is used for making conveyor belts.
→ Poly Ethene Tetraphthalate (PET):
- It is used for making bottles and containers for soft drinks and food.
- It is used for making tapes for audio and video cassettes.
→ Acrylic Fibres (Acrylon): Acrylic fibres resemble wool. These are used for making sweaters and shawls.
It is used for making blankets, which are very light and provide the same warmth as woolen blankets.
→ Advantages of Synthetic Fibres:
- They have long-lasting lustre.
- They are more durable; compared to natural fibres.
- They are easy to clean and dry very quickly.
- They are wrinkle free and do not need ironing.
- They do not shrink on washing.
- They are less expensive than natural fibres.
→ Disadvantages of Synthetic Fibres:
- They have very low melting point and they burn to form small sticking beads at high temperature. They are a potential fire hazard.
- They don’t absorb sweat and hence it is uncomfortable to wear them; especially in summer and rainy seasons.
Synthetic fibres are not biodegradable and thus cause lot of pollution.
→ Plastics: Plastics are polymers of simple molecules (monomers). There are two types of arrangement of monomers in plastics, i.e. linear arrangement and cross-linked arrangement.
- Linear Arrangement: In this arrangement, the monomers are arranged in a straight chain. Plastics formed because of linear arrangement are generally known as thermoplastic.
- Cross-linked Arrangement: In this arrangement, the monomers are formed from cross- linked chains of monomers. This type of plastic is generally known as thermosetting plastic.
→ Thermoplastic: These plastics can be easily deformed on heating and can be moulded into a new shape.
→ Thermosetting plastic: These plastics cannot be remoulded again by gentle heating. Moulding in these plastics is permanent. Bakelite and melamine are examples of thermosetting plastics.
→ Bakelite: Bakelite is a poor conductor of heat. It is used in making electrical switches, handles of utensils, etc.
→ Melamine: Melamine can resist fire. It is used in making kitchenware and fire-resistant fabric.
→ Characteristics of Synthetic Plastics:
- Light weight
- High tensile strength
- Resistance to chemicals
- Non-biodegradable
- Lustrous and colourful
→ Damage Caused by Plastic Waste:
- Plastic carrybags and other articles clog the city drainage system.
- Stray cows and other animals often swallow polythene bags and wrappers. This cnokas their digestive tract and results in the death cf the animal.
- Plastic is non-biodegradable and hence creates a burden on the environment.
- When plastic is burnt, it produces harmful gases which pollute the air.
→ Measures to Centre the Damage Caused by Plastic Waste:
- Do not throw plastic wrappers carelessly on road.
- Biodegradable and non-biodegradabie waste should be collected separately and disposed off separately.
- Use cotton or jute bags for shopping. Say no to plastic bags.
- Remember four R’s, i.e. Reduce, Reuse, Recycle and Recover.
→ Syntnetic f bres : Fibres which are made in laboratories or factories.
→ Monomer : Simple molecular units which are used tnr making synthetc fibres.
→ Polymer : A chain of many monomers.
→ Polyrnerization : The process of making polymers from simple molecules.
→ Four R’s of Conservation: Reduce, Reuse, Recycle and Recover.