Synthetic Fibres and Plastics - Complete Guide for Class 8

Synthetic fibres and plastics have revolutionised modern life. Unlike natural fibres obtained from plants (cotton, jute) and animals (wool, silk), synthetic fibres are man-made through chemical processes.

Why Study This Topic?

• Understand everyday materials around you
• Learn about polymer chemistry basics
• Develop awareness about environmental impact
• Important for CBSE Class 8 Science exams

Synthetic materials are created by joining small molecules called monomers into long chains called polymers through a process called polymerization.

What Are Fibres?

Fibre is a thread-like strand used to make fabrics and textiles.

Types of Fibres

What Are Synthetic Fibres?

Synthetic fibres are artificially manufactured fibres made from chemical substances derived primarily from petroleum products.

• Made from polymers (long chain molecules)
• Created through polymerization
• Raw materials: coal, petroleum
• Can be customized for different properties

Major Types of Synthetic Fibres

1. Rayon (Artificial Silk)

What is Rayon?

Rayon is a semi-synthetic fibre made from cellulose obtained from wood pulp.

Manufacturing Process:

1. Wood pulp is dissolved in sodium hydroxide (alkaline solution)
2. This forms a sticky liquid called viscose
3. Viscose is forced through tiny holes (spinnerets) into sulphuric acid
4. Silk-like threads of rayon are formed

Properties:

• Chemically similar to cotton
• Has shine like silk (called artificial silk)
• Can be dyed easily
• Lustrous and smooth
• Can be blended with cotton or wool

Uses:

• Making fabrics (sarees, dress materials)
• Blended with wool for carpets
• Reinforced tyres
• Medical bandages and surgical dressings

Why used in medical field?

Rayon is highly absorbent, soft, and does not cause skin irritation, making it ideal for bandages.

2. Nylon

What is Nylon?

Nylon was the first fully synthetic fibre, made from coal, water, and air. It's a polyamide polymer.

Origin of Name: NYLON = New York + LONdon (cities where it was developed)

Properties:

• Extremely strong and elastic
• Lightweight
• Lustrous appearance
• Water-resistant (absorbs very little water)
• Does not wrinkle easily
• Resistant to moths and chemicals
• Very durable

Uses:

• Parachutes and ropes (due to high strength)
• Fishing nets
• Tyre cords
• Toothbrush bristles
• Stockings, socks, sportswear
• Seat belts

3. Polyester

What is Polyester?

Polyester is made from repeating units of ester (organic compounds with fruity smell). The raw materials come from petroleum.

Common Trade Name: Terylene

Properties:

• Does not wrinkle easily (crease-resistant)
• Remains crisp and fresh
• Easy to wash and dries quickly
• Strong and durable
• Can be drawn into very fine fibres

Uses:

• Dress materials (shirts, trousers, sarees)
• Blended fabrics:
  • Terrycot = Terylene + Cotton
  • Terrywool = Terylene + Wool
• Boat sails
• Conveyor belts
• Bottles and containers (PET)

PET (Polyethylene Terephthalate):

• A form of polyester used as plastic
• Lightweight, transparent, and shatterproof
• Used for bottles, jars, containers
• Replacing glass in many applications

4. Acrylic

What is Acrylic?

Acrylic fibre is made from acrylonitrile through polymerization.

Properties:

• Soft and light like wool
• Warm and comfortable
• Weather-resistant
• Strong and durable
• Quick-drying (absorbs very little water)

Uses:

• Sweaters and woolen garments
• Blankets and shawls
• Cheaper alternative to wool
• Outdoor clothing

Comparison Table: Synthetic Fibres

Characteristics of Synthetic Fibres

Advantages

• Strong and durable - Last longer than natural fibres
• Wrinkle-resistant - Stay fresh and crisp
• Quick-drying - Absorb very little water
• Easy to maintain - Simple to wash and care for
• Moth-resistant - Not attacked by insects
• Cost-effective - Generally cheaper than natural fibres
• Versatile - Can be blended with natural fibres
• Independent of agriculture - Don't depend on crops or animals

Disadvantages

• Flammable - Catch fire easily and melt
• Low melting point - Damaged by heat
• Generate static electricity - Stick to body
• Non-biodegradable - Environmental pollution
• Uncomfortable in hot weather - Don't absorb sweat well

Safety Warning: Never wear synthetic clothes while working in kitchen or near fire. They can melt and stick to skin, causing severe burns.

CBSE Class 8 Science Notes Chapter-wise

What Are Plastics?

Plastic is a synthetic material that can be molded into desired shapes when soft and hardens to produce durable articles.

The word "plastic" means easy to mold.

Features

• Made from polymers (like synthetic fibres)
• Raw materials: petroleum and coal
• Can be shaped, colored, and molded
• Non-reactive with water and air

Types of Plastics

Plastics are classified based on their behavior when heated:

1. Thermoplastics

Plastics that can be softened repeatedly by heating and molded into new shapes.

Structure: Linear arrangement of monomers (no cross-linking)

Examples:

• Polythene (Polyethylene)
• PVC (Polyvinyl Chloride)
• Polystyrene
• Nylon
• Polyester

Properties:

• Can be remolded
• Soften on heating
• Recyclable

Uses:

• Carry bags
• Bottles and containers
• Pipes and tubes
• Wire insulation

2. Thermosetting Plastics

Plastics that can be molded only once. Once set, they cannot be softened again by heating.

Structure: Cross-linked arrangement of monomers

Examples:

• Bakelite
• Melamine
• Formaldehyde resin

Properties:

• Cannot be remolded
• Resistant to heat
• Strong and rigid
• Good electrical insulators

Uses:

• Electrical switches and plugboards
• Handles of cookware (pressure cooker handles)
• Floor tiles
• Coating for non-stick cookware

Comparison: Thermoplastics vs Thermosetting Plastics

Common Plastics: Properties and Uses

1. Polythene (Polyethylene)

Preparation: Polymerization of ethene (CH₂=CH₂)

Types:

• LDPE (Low Density Polyethylene) - Flexible, used in bags
• HDPE (High Density Polyethylene) - Rigid, used in containers

Properties:

• Insoluble in all solvents
• Not affected by strong chemicals
• Non-biodegradable
• Lightweight

Uses:

• Carry bags and packaging
• Bottles and containers
• Electric wire insulation
• Anti-corrosion coating

2. PVC (Polyvinyl Chloride)

Preparation: Polymerization of vinyl chloride

Properties:

• Flexible and durable
• Water-resistant
• Chemical-resistant

Uses:

• Raincoats and handbags
• Floor covering (vinyl flooring)
• Shoe soles
• Water pipes and sanitary fittings
• Wire insulation
• Garden hoses

3. Polystyrene

Properties:

• Lighter than polythene
• Can be molded easily
• When air is blown through molten polystyrene, it forms foam (Thermocole)

Uses:

• Disposable cups and plates
• Packaging material (thermocole)
• Insulation in refrigerators
• Ice boxes

4. Teflon (Polytetrafluoroethylene)

Properties:

• Non-stick surface (oil and water don't stick)
• Heat-resistant
• Chemically inert

Uses:

• Non-stick coating on cookware (frying pans)
• Lubricant in machinery
• Electrical insulation

5. Bakelite

Type: Thermosetting plastic

Properties:

• Hard and rigid
• Good electrical insulator
• Heat-resistant
• Does not soften on heating

Uses:

• Electrical switches and plugs
• Cabinet for radios and TVs
• Handles for utensils
• Telephone bodies

6. Melamine

Type: Thermosetting plastic

Properties:

• Fire-resistant
• Heat-resistant
• Doesn't break easily

Uses:

• Floor tiles
• Kitchenware (plates, cups)
• Coating for fabrics (fire-resistant uniforms)
• Laminated sheets for furniture

Characteristics of Plastics

Physical Properties

Chemical Resistance:

• Hardly affected by acids and alkalis
• Non-reactive with water and air
• Long-lasting and corrosion-free

Weather Resistance:

• Not biodegradable
• Can last for hundreds of years
• Resistant to decay

Lightweight:

• Much lighter than metals
• Easy to transport and handle

Strength:

• Can withstand significant force
• Durable and tough

Insulation:

• Poor conductors of heat and electricity
• Used for wire coating and handles

Appearance:

• Can be transparent or colored
• Can be made in any texture

Plastic Codes: Understanding Recycling Symbols

Plastics and Environment

The Problem with Plastics

Non-Biodegradable Nature:

• Plastics do not decompose by natural processes
• Can remain in environment for hundreds of years
• Accumulate as waste

Environmental Impact:

• Clog drainage systems
• Harm wildlife (animals eat plastic waste)
• Pollute oceans (plastic islands forming)
• Toxic gases released when burned
• Contribute to soil pollution

Health Hazards:

• Burning plastics release poisonous gases
• Can cause respiratory problems
• Microplastics enter food chain

Biodegradable vs Non-Biodegradable Materials

Biodegradable Materials

Materials that can be broken down by natural processes (bacteria, fungi) into simpler substances.

Examples:

• Vegetable and fruit peels (1-2 weeks)
• Paper (10-30 days)
• Cotton cloth (2-5 months)
• Wood (10-15 years)
• Woolen clothes (about 1 year)

Benefits:

• Decompose naturally
• Return nutrients to soil
• Environmentally friendly

Non-Biodegradable Materials

Materials that cannot be broken down by natural processes and persist in the environment.

Examples:

• Plastics (several hundred years)
• Glass (thousands of years)
• Metals (100-500 years)
• Synthetic fibres

Problems:

• Accumulate as waste
• Cause pollution
• Harm ecosystem

The 3Rs to Save Environment

1. Reduce

Minimize plastic use:

• Use cloth bags instead of plastic bags
• Avoid disposable plastic items
• Buy products with minimal packaging
• Choose alternatives to plastic

2. Reuse

Use plastic items multiple times:

• Reuse plastic containers for storage
• Use carry bags multiple times
• Donate old items instead of throwing
• Repair items instead of replacing

3. Recycle

Convert waste plastic into new products:

• Segregate recyclable plastics
• Send to recycling centers
• Support recycled products
• Participate in collection drives

4th R - Refuse: Say no to single-use plastics!

Enhanced Study Notes

Quick Revision Points

Synthetic Fibres:

1. Made from petrochemicals through polymerization
2. Four main types: Rayon, Nylon, Polyester, Acrylic
3. Rayon = semi-synthetic (from cellulose)
4. Nylon = first fully synthetic fibre (strongest)
5. Polyester = wrinkle-resistant (Terylene)
6. Acrylic = synthetic wool

Plastics:

1. Moldable synthetic materials
2. Two types: Thermoplastics and Thermosetting
3. Thermoplastics can be remolded (recyclable)
4. Thermosetting plastics cannot be remolded
5. Examples: Polythene, PVC, Bakelite, Melamine

Environmental Concerns:

1. Non-biodegradable nature
2. Pollution problems
3. Apply 3Rs: Reduce, Reuse, Recycle

Memory Tricks & Mnemonics

RNPA for Synthetic Fibres:

• Rayon (artificial silk)
• Nylon (strong like steel)
• Polyester (no wrinkles)
• Acrylic (artificial wool)

Thermoplastic vs Thermosetting:

• Thermo-PLASTIC = can be PLASTERED again (remolded)
• Thermo-SETTING = once SET, stays SET (cannot remold)

Remember PET:

• Poly Ethylene Terephthalate
• Used in PET bottles

Biodegradable Timing:

• Paper = 1 month
• Cotton = 3 months (roughly)
• Wood = 10+ years
• Plastics = 100+ years

Summary Table for Quick Revision

Solved Examples

Q: What are synthetic fibres? How are they different from natural fibres?

Solution: Synthetic fibres are man-made fibres created by chemical processing of petroleum products through polymerization.

Differences:

Q: Why is rayon called artificial silk? Give two uses of rayon.

Solution:

Rayon is called artificial silk because:

• It has a lustrous, shiny appearance like silk
• It feels smooth and soft like silk
• But it's chemically similar to cotton (made from cellulose)

Uses of Rayon:

1. Making fabrics (sarees, dress materials)
2. Medical bandages and surgical dressings (highly absorbent)

Q: Why are ropes made from nylon preferred for rock climbing and parachutes?

Solution:

Nylon ropes are preferred because:

1. High tensile strength - A nylon thread is stronger than a steel wire of same thickness
2. Elastic - Can stretch and bear shock loads
3. Lightweight - Easy to carry
4. Weather-resistant - Not affected by moisture
5. Durable - Long-lasting

These properties make nylon ideal for safety equipment where strength and reliability are crucial.

Q: What is PET? Write its properties and uses.

Solution:

PET = Poly Ethylene Terephthalate

It is a form of polyester used as plastic.

Properties:

• Very lightweight
• Transparent and colorless
• High transparency
• Strong and impact-resistant
• Shatterproof (unlike glass)

Uses:

• Making bottles for water, soft drinks
• Jars for storing food items
• Containers and utensils
• Replacing glass in many applications

Q: Differentiate between thermoplastics and thermosetting plastics with examples.

Solution:

Q: Why are handles of pressure cookers made of thermosetting plastics and not thermoplastics?

Solution:

Handles of pressure cookers are made from thermosetting plastics (like Bakelite) because:

1. Heat resistance - They don't soften when exposed to high temperatures
2. Rigidity - Remain hard and strong even when hot
3. Safety - Won't melt or deform during cooking
4. Poor heat conductor - Don't transfer heat to hands

Thermoplastics would soften and melt at cooking temperatures, making them unsafe.

Q: Why is plastic considered harmful to the environment?

Solution:

Plastics are harmful because:

1. Non-biodegradable - Don't decompose naturally
2. Persist for centuries - Remain in environment for 100+ years
3. Pollute soil and water - Contaminate ecosystems
4. Harm wildlife - Animals eat plastic waste and die
5. Clog drainage - Block water flow in cities
6. Toxic when burned - Release poisonous gases
7. Accumulate as waste - Create plastic islands in oceans

Q: Arrange the following in order of time taken to degenerate: Cotton cloth, Paper, Plastic bag, Wood

Solution:

Order (fastest to slowest degradation):

1. Paper - 10-30 days
2. Cotton cloth - 2-5 months
3. Wood - 10-15 years
4. Plastic bag - Several hundred years

Paper degrades fastest, plastic takes the longest.

Q: Why should we not wear synthetic clothes while working in the kitchen or laboratory?

Solution:

We should avoid synthetic clothes near fire because:

1. Low melting point - Synthetic fibres melt easily when heated
2. Catch fire quickly - More flammable than natural fibres
3. Stick to body - Melted fabric adheres to skin
4. Cause severe burns - Can result in serious injuries

Safe alternative: Wear cotton clothes which don't melt and are less flammable.

Q: What are polymers? How are they formed? Give examples.

Solution:

Polymers are large molecules made up of many small repeating units called monomers.

Formation Process (Polymerization):

1. Small molecules (monomers) are chemically joined
2. They form long chains
3. This process is called polymerization

Example:

• Ethene molecules (monomer) → Polythene (polymer)
• CH₂=CH₂ + CH₂=CH₂ + CH₂=CH₂... → (-CH₂-CH₂-)ₙ

Examples of Polymers:

• Natural: Cotton (cellulose), Silk, Wool
• Synthetic: Nylon, Polyester, PVC

Q: Assertion (A): Rayon is called a semi-synthetic fibre.
Reason (R): Rayon is made from natural cellulose but through chemical processing.

Options: (a) Both A and R are true, R is correct explanation of A
(b) Both A and R are true, R is not correct explanation of A
(c) A is true, R is false
(d) A is false, R is true

Solution:(a) Both A and R are true, R is correct explanation of A

Explanation: Rayon is indeed semi-synthetic because it starts with natural cellulose (from wood pulp) but undergoes extensive chemical processing to become rayon. The reason correctly explains why it's called semi-synthetic.

Q: Match the following:

Solution:

• (i) Polyester → (c) Terylene (Terylene is a polyester)
• (ii) Teflon → (b) Non-stick coating (used on cookware)
• (iii) Acrylic → (a) Synthetic wool (soft and warm)
• (iv) Bakelite → (d) Electrical switches (good insulator)

Q: Ravi bought a new jacket. The label said "100% Polyester". His friend told him it's better than cotton.
(a) What is polyester?
(b) Give two advantages of polyester over cotton.
(c) What precaution should Ravi take while wearing this jacket?

Solution:

(a) Polyester is a synthetic fibre made from petroleum products through polymerization of ester units.

(b) Advantages over cotton:

1. Wrinkle-resistant - Stays crisp without ironing
2. Quick-drying - Absorbs very little water
3. More durable - Lasts longer
4. Easy maintenance - Simple to wash

(c) Precaution: Ravi should avoid wearing it near fire or while cooking because polyester can easily catch fire and melt, sticking to the skin and causing severe burns.

Q: Can we recycle all types of plastics? Explain.

Solution:

No, we cannot recycle all types of plastics.

Recyclable Plastics (Thermoplastics):

• Polythene
• PVC
• Polystyrene
• Can be melted and remolded

Non-Recyclable Plastics (Thermosetting):

• Bakelite
• Melamine
• Once set, cannot be softened again
• Cannot be remolded

Reason: The difference lies in their molecular structure. Thermoplastics have linear chains that can be broken and reformed, while thermosetting plastics have cross-linked chains that cannot be broken without destroying the material.

Q: Compare the properties of nylon and cotton. Which is better for making ropes and why?

Solution:

Comparison:

Better for ropes: NYLON

Reasons:

1. Much stronger - Can bear heavy loads
2. Water-resistant - Won't rot when wet
3. More durable - Lasts longer outdoors
4. Elastic - Can stretch without breaking

Cotton ropes absorb water, become heavy, can rot, and are weaker - making them unsuitable for heavy-duty applications.

Q: Your mother wants to buy kitchen containers. The shopkeeper shows her plastic and glass containers. Which should she choose and why?

Solution:

Better choice: Plastic containers (made of PET or food-grade plastic)

Advantages of plastic containers:

1. Lightweight - Easy to handle
2. Shatterproof - Won't break if dropped
3. Non-reactive - Don't react with food
4. Durable - Last long
5. Affordable - Cheaper than glass

Advantages of glass:

1. Non-toxic - No chemical leaching
2. Can be heated - Microwave safe
3. Eco-friendly - Recyclable
4. Doesn't stain or absorb odors

Best choice: Use plastic for dry storage (rice, pulses) and glass for storing liquids and items to be heated. This combines the benefits of both.

Q: How does plastic waste affect marine life? Suggest two ways to reduce this problem.

Solution:

Effects on marine life:

1. Entanglement - Marine animals get trapped in plastic waste
2. Ingestion - Fish, turtles, and birds eat plastic thinking it's food
3. Starvation - Plastic fills stomach but provides no nutrition
4. Toxic chemicals - Plastics release harmful substances in water
5. Habitat destruction - Plastic waste damages coral reefs and ocean floor

Ways to reduce:

1. Avoid single-use plastics - Use reusable bags, bottles, and containers
2. Proper disposal - Don't throw plastic in water bodies; recycle properly
3. Beach clean-ups - Participate in coastal cleaning drives
4. Support biodegradable alternatives - Use eco-friendly products

Q: Explain the 3Rs concept with examples for each.

Solution:

1. REDUCE - Minimize use of plastics

Examples:

• Use cloth bags instead of plastic bags
• Buy products with less packaging
• Avoid disposable plastic items (plates, cups, spoons)
• Use steel/copper water bottles instead of plastic

2. REUSE - Use items multiple times

Examples:

• Reuse plastic containers for storage
• Use carry bags multiple times
• Donate old clothes and toys
• Refill bottles instead of buying new ones

3. RECYCLE - Convert waste into new products

Examples:

• Segregate recyclable plastics
• Send to recycling centers
• Support products made from recycled material
• Participate in collection drives

Added 4th R: REFUSE

• Say no to single-use plastics
• Refuse unnecessary packaging

Q: You are given four fabric samples but labels are missing. How will you identify which is cotton, wool, polyester, and nylon using the fire test?

Solution:

Fire Test Method:

1. Cotton:

• Burns with steady flame
• Smells like burning paper
• Leaves soft gray ash
• Continues to burn after flame removed

2. Wool:

• Burns slowly
• Smells like burning hair
• Forms hard black bead when cooled
• Self-extinguishes when flame removed

3. Polyester:

• Melts and shrinks away from flame
• Forms hard black bead
• Sweet chemical smell
• Continues to burn with black smoke

4. Nylon:

• Melts quickly
• Forms hard plastic-like bead
• Celery-like smell
• Doesn't continue burning easily

Safety Note: Perform this test under adult supervision with proper safety measures.

Q: Write a detailed note on plastics covering:

(a) Definition

(b) Types

(c) Properties

(d) Environmental concerns

Solution:

(a) Plastics are synthetic materials made from polymers that can be molded into desired shapes when soft and hardened to produce durable articles. The word "plastic" means "easy to mold."

(b) Types:

Based on heating behavior:

1. Thermoplastics:
   • Can be softened and remolded repeatedly
   • Linear polymer structure
   • Examples: Polythene, PVC, Polystyrene
   • Recyclable
2. Thermosetting Plastics:
   • Can be molded only once
   • Cross-linked polymer structure
   • Examples: Bakelite, Melamine
   • Non-recyclable

(c) Properties:

• Non-reactive - Resistant to chemicals
• Lightweight - Easy to handle
• Durable - Long-lasting
• Poor conductors - Don't conduct heat/electricity
• Moldable - Can be shaped easily
• Versatile - Available in various colors and textures

(d) Environmental concerns:

• Non-biodegradable - Don't decompose naturally
• Pollution - Contaminate soil and water
• Harm wildlife - Animals ingest plastic
• Clogging - Block drainage systems
• Toxic fumes - Release harmful gases when burned
• Long persistence - Remain for hundreds of years

Solutions: Practice 3Rs (Reduce, Reuse, Recycle) and use biodegradable alternatives.

Q: Assertion (A): Thermosetting plastics are used for making electrical switches.
Reason (R): Thermosetting plastics are poor conductors of electricity and heat.

Solution:(a) Both A and R are true, R is correct explanation of A

Thermosetting plastics like Bakelite are indeed used for electrical switches because they are poor conductors of electricity (good insulators), preventing electric shocks. They're also heat-resistant and don't soften, making them safe for electrical applications. The reason correctly explains the assertion.

Q: A plastic bag takes approximately 500 years to decompose. If a person uses 2 plastic bags daily, how many bags would be added to the environment in a year? If a city has 1 million people with similar usage, calculate the annual plastic bag waste.

Solution:

For one person:

• Bags per day = 2
• Days in year = 365
• Bags per year = 2 × 365 = 730 bags

For city of 1 million people:

• Population = 1,000,000
• Bags per person per year = 730
• Total bags = 1,000,000 × 730 = 730,000,000 bags
• That's 730 million plastic bags per year

Impact: All these bags will remain in the environment for 500 years, accumulating year after year.

Conclusion

Synthetic fibres and plastics have transformed modern life with their versatility, durability, and affordability. However, their non-biodegradable nature poses significant environmental challenges.

• Synthetic fibres (Rayon, Nylon, Polyester, Acrylic) are made through polymerization
• Plastics are of two types: Thermoplastics (recyclable) and Thermosetting (non-recyclable)
• While useful, plastics cause severe environmental pollution
• Practice the 3Rs: Reduce, Reuse, Recycle

For exam success:

• Understand properties and uses of each fibre type
• Know the differences between thermoplastics and thermosetting plastics
• Remember biodegradability times
• Practice diagram-based questions
• Focus on environmental impact questions