Synthetic Fibres and Plastics Question Answers: NCERT Class 8 Science

The fibres which are made by man are called as man- made or synthetic fibres. These fibres are made by man with the help of chemicals. Rayon, Nylon, Polyester are some examples of synthetic or man- made fibres.

Plastics are non- corrosive in nature because plastics are non- degradable substances. Plastics remain unreactive in nature while they comes in contact of strong acids. Generally plastics are used to store things.

No, the handle and bristles of tooth brush are made up of different types of materials. The bristles are soft and flexible whereas the handles of brush are hard enough.

Plastics are non- degradable substance. Plastic cannot be decomposed by micro- organisms. On burning, plastics cannot burnt fully and also releases harmful and poisonous gases or chemicals in the environment. Plastic bags are thrown into the garbage. Sometimes animals like cow, dog, swallow; plastic polythene which choke their respiratory tract which lead to their death. That is why we should avoid the use of plastics.

                                   Column I                                         Column II                                                

                 Poyester                                           (d) Fabrics do not wrinkle easily

                 Teflon                                                (c) used to make non- stick cookware

                 Rayon                                               (a) prepared by using wood pulp

                 Nylon                                                (b) used for making parachutes and stockings

• Polyester is a synthetic fibre which is made by man with the help of chemicals. A fabric made up of polyester do not wrinkled easily.
• Teflon is a synthetic materials which is used in making non- stick cookware.
• Rayon is different from synthetic fibres, it is obtained from wood pulp.
• Nylon has a very high tensile strength. So it is used in making parachutes and stockings.

Manufacturing synthetic fibres is actually helping conservation of forests because for natural fibres, raw materials is obtained from the plants. For this a number of trees are cut down. But for synthetic fibres, raw material is obtained from the petrochemicals. So we can say that synthetic fibres helps in the conservation of forests.

With the help of an activity, we can see that thermoplastic are poor conductor of electricity.

Requirements: Bulb, some wires, battery, a piece of metal, plastic pipe.

Procedure:

• Set up the first circuit with the help of metal and with the plastic pipe.
• Now, switch on the current. Here you observed that the bulb will glow in the first case.
• In later case, the bulb will no glow. It shows that the plastic pipe is the poor conductor of electricity.

(b) It is obtaiuned from wood pulp

Rayon is different from synthetic fibres, as it is obtained from the wood pulp.

(a) Artificial, man- made

The fibres which are made by man with the help of chemicals are called as artificial or man- made fibres.

(b) Petrochemicals

Synthetic or man- made fibre is derived from the chemical or we can say petrol originated chemicals.

(c) Polymer

Plastics are also polymers. Polymers are the big chain of small units which are joined together.

Nylon fibre is very strong. It is used in making ropes which are used for mountain climbing. It is also used in making parachutes. It has a very high tensile strength.

Chemical containers are favoured for storing food because of the following reasons:

1. Plastics are generally cheap or lower in price.
2. Due to having light weight.
3. Plastics have a good strength. Plastics are easy to handle.

Generally plastics are of two types: Thermoplastic and Thermosetting.

Differences between Thermoplastic and Thermosetting are as follows:

(a) Saucepan handles

Thermosetting plastic is the hard plastic which cannot be softened easily on heating. Saucepan handles are made up of thermosetting plastic because thermosetting plastic is a poor conductor of heat.

(b) Electric plugs/ Switches/ Plug boards

Thermosetting plastic are the poor conductor of heat and electricity. Hence, Thermosetting Plastic is used to make electric plug or switches or plug boards to prevent from electric shock.

The things which are made up of thermoplastic can be broke down easily. So, the things can be recycled easily in comparison to the things which are made up of thermosetting plastic.

Rana should buy a cotton shirt because cotton is a bad conductor of heat and a good absorber of water also. Evaporation of sweat occurs quickly in cotton and gives a cool sensation. So, we advise Rana to buy a shirt which is made up of cotton instead of a synthetic shirt.