Synthetic Fibres & Plastics Summary Class 8 NCERT Summary

Introduction

• Fabrics are made from fibres obtained from natural or artificial sources.
• They are also used for making a large variety of household articles.

Synthetic fibres (or man-made fibres)

• They are chains of small units joined together (each small unit is a chemical substance).
• These small units combine to form a large single unit called a polymer.

Types of polymers

Addition polymers

• Monomers combine together to form a giant molecule known as the polymer. No molecule is eliminated during formation of addition polymers.
•  Exmples of addition polymer are polythene, polyvinyl chloride etc.

Condensation polymers

• Several small units of monomers combine with each other, along with elimination of simple molecule like water to form polymer unit.
• Examples of condensation polymer are nylon-66, terylene etc.

Polyester

• Fabric made from polyester does not get wrinkled easily.
• Common polyester includes terylene and PET
• PET is used for making utensils, films, wires, bottles, etc. Terylene is used for making dress materials.

Acrylic

• It is relatively cheaper than wool.
• Sweaters, shawls and blankets are made from acrylic.

Characteristics of synthetic fibres

• They dry up quickly, are durable, less expensive, readily available, and easy to maintain.
• However, fabric made of synthetic fibre melts on catching fire and sticks to the body of person wearing it.
• So, synthetic clothes should not be worn while working in kitchen or laboratory.

Plastics

• They are polymer-like synthetic fibres.
• Arrangement of small units is linear or cross-linked.
• Can be recycled, reused, coloured, melted, rolled into sheets, or made into wires.

Thermoplastics

• These are the plastics that get deformed easily on heating and can be bent easily. Examples: polythene and PVC

Thermosetting plastics

• These are the plastics, which when moulded once, cannot be softened by heating. Examples: bakelite and melamine

Characteristics of plastics

• They are non-reactive.
• They are light, strong, and durable.
• They are poor conductors of heat and electricity.

Use of plastics

• They are used to store various kinds of materials such as food items, chemicals etc.
• It is widely used in various industries and for making a variety of household articles.
• They are extensively used in health care industry for making syringes, threads for stitching wounds, doctor’s gloves, and other medical instruments.
• Fire resistant plastics are used as a coating on the suits of the firemen.

Biodegradable substances

• These are the materials that decompose through natural processes such as by the action of bacteria.
  Examples: paper, peels of vegetables, wood and fruits, etc.

Non-biodegradable substances

• These are the materials that are not easily decomposed by natural processes. Examples: plastic bags, metals, etc.
• Plastics are not environment friendly as they cause environment pollution.
• To minimize the environmental hazards, the 4R principle must be used.
• Reduce, Reuse, Recycle, and Recover.