Class 8 Science (CTET Paper 2)Critical (2–3 MCQs guaranteed)9 min read
Chapter 3: Synthetic Fibres and Plastics
संश्लेषित रेशे और प्लास्टिक (रेयॉन, नायलॉन, टेरीलीन, थर्मोप्लास्टिक एवं थर्मोसेटिंग प्लास्टिक)
CTET Theme: Polymer Chemistry & Material Science
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OVERVIEW1 of 16
Introduction: Synthetic Fibres and Plastics
Welcome to Mentora CTET Audio Masterclass for Class 8 Science (CTET Paper 2), Chapter 3: Synthetic Fibres and Plastics. Here are the high-yield facts tested in CBSE examinations.
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High-Weightage NCERT Facts & Key Terms (द्विभाषी)
12 Core Points- Polymers: Large single units formed by repeating chains of smaller chemical monomers (e.g. Cotton is cellulose polymer of glucose).
- Classification of Major Synthetic Fibres:
- - Rayon (Artificial Silk / कृत्रिम रेशम): Obtained from chemical treatment of natural WOOD PULP. Although derived from natural cellulose, it is classified as a semi-synthetic fibre; dyed in bright shades, woven like silk, and blended with cotton to make bedsheets or wool to make carpets.
- - Nylon (नायलॉन): First 100% fully synthetic fibre prepared without any natural raw materials (made from coal, water, and air in 1931). Strong, elastic, lightweight, lustrous, easy to wash. A NYLON THREAD IS STRONGER THAN A STEEL WIRE OF EQUAL THICKNESS! Used for parachutes, rock climbing ropes, socks, bristles of toothbrushes.
- - Polyester (पॉलिएस्टर): Fabric does not wrinkle easily; remains crisp and easy to wash. Terylene is a popular polyester; PET (Polyethylene Terephthalate) is used for bottles, jars, utensils, and films.
- - Acrylic (एक्रिलिक): Synthetic wool substitute; cheap, durable, available in variety of shades; resistant to moths compared to natural wool.
- Thermoplastics vs Thermosetting Plastics (Guaranteed CTET Distinction):
- - Thermoplastics (थर्मोप्लास्टिक): Deform easily on heating and can be melted and remolded repeatedly (Linear or loosely cross-linked polymer chains). Examples: Polythene (पॉलिथीन), PVC (Polyvinyl Chloride - electrical wire insulation, drainage pipes), toys, combs.
- - Thermosetting Plastics (थर्मोसेटिंग प्लास्टिक): When molded once, CANNOT be softened by heating (heavily cross-linked 3D network).
- * Bakelite (बैकेलाइट): Poor conductor of heat and electricity. Used for electrical switches, plugs, sockets, and handles of cookware/frying pans.
- * Melamine (मेलामाइन): Versatile flame-resistant material; withstands heat better than other plastics. Used for floor tiles, microwave kitchenware, and flame-retardant uniforms for firemen.
- Environmental Awareness: Plastics are non-biodegradable; 5R principle: Reduce, Reuse, Recycle, Recover, Refuse.
CBSE Distractor Traps (Avoid Negative Marking)
- Trap: Is Rayon completely synthetic like Nylon? Correct: NO. Rayon is derived from natural wood pulp treated with chemicals (semi-synthetic). Nylon was the FIRST fully synthetic fibre.
- Trap: What plastic is used to make cookware handles and electrical switches? Correct: BAKELITE (thermosetting), because it resists heat and conducts zero electricity.
- Trap: Why do firemen's uniforms resist fire? Correct: They have a coating of MELAMINE plastic, which is flame-resistant.
NCERT Core Facts: Polymer Science & Plastics Engineering
Synthetic fibre classifications and plastic thermal behavior appear constantly in CTET Paper 2:
1. Synthetic Fibre Diagnostic Table
| Fibre | Raw Material Origin | Unique Physical Property | High-Yield Application |
|---|---|---|---|
| Rayon (रेयॉन) | Natural wood pulp + chemical reagents | Drapes like luxury silk at fractional cost | Blended with cotton for luxury bedsheets |
| Nylon (नायलॉन) | Coal, water, and air (100% synthetic) | Tensile strength exceeding steel wire | Parachute canopies, rock climbing ropes |
| Polyester (PET) | Petroleum esters | Wrinkle-resistant, non-absorbing | Shatterproof beverage bottles, dress fabric |
| Acrylic (एक्रिलिक) | Polyacrylonitrile | Warmth comparable to wool; moth-proof | Inexpensive blankets, cardigans, shawls |
2. Thermoplastics vs. Thermosetting Plastics
THERMOPLASTIC (Linear polymer chains)
─── Heat melts it ───> Can be remolded into new shapes repeatedly
Examples: Polythene bags, PVC electrical insulation pipes, plastic toys
THERMOSETTING (Heavily cross-linked 3D lattice)
─── Heat does NOT soften it once molded ───> Retains permanent shape
Examples:
* Bakelite (बैकेलाइट): Electrical switches, saucepan handles
* Melamine (मेलामाइन): Flame-retardant fire fighter uniforms, unbreakable crockeryOfficial CTET Benchmark Test
Test Your Mastery: Synthetic Fibres and Plastics
Authentic CBSE exam questions tested directly from this NCERT chapter.
Question 1 of 2(CTET Jan 2022 & Aug 2023)
A material X is obtained from chemical treatment of natural wood pulp. It feels like silk and can be dyed in vibrant colors. Material X is:
एक पदार्थ X प्राकृतिक काष्ठ लुगदी के रासायनिक उपचार से प्राप्त होता है। यह रेशम जैसा लगता है और इसे जीवंत रंगों में रंगा जा सकता है। पदार्थ X क्या है?
Question 2 of 2(CTET Dec 2021)
Which pair of materials belongs exclusively to the category of 'Thermosetting Plastics'?
पदार्थों का कौन-सा युग्म विशेष रूप से 'थर्मोसेटिंग प्लास्टिक' की श्रेणी से संबंधित है?
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Why is nylon chosen for manufacturing parachutes and mountaineering ropes?
Because nylon is exceptionally strong, lightweight, elastic, and has a tensile strength greater than an equivalent steel wire.
Why are saucepans and frying pan handles made of thermosetting bakelite rather than thermoplastic PVC?
Bakelite does not soften or deform when exposed to high cooking temperatures and is an excellent thermal insulator.