Notes of Ch 3 Synthetic Fibres and Plastics| Class 8th Science

Study Material and Notes of Ch 3 Synthetic Fibres and Plastics Class 8th Science

Topics in the Chapter

• Introduction
• Synthetic fibres or man-made fibres
• Types of polymers
• Polyster
•  Acrylic
• Plastics
→ Thermoplastics
→ Thermosetting plastics
→ Characteristics of plastics
→ Uses of plastics
• Biodegradable substances
• Non-biodegradable substances

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.

→ Examples 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.

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