Synthetic Fibers

Synthetic Fibers and Plastics: Complete Guide for CBSE Class 8 Science

Introduction to Synthetic Fibers

Synthetic fibers are man-made fibers created through chemical processes using raw materials derived from petroleum products called petrochemicals. Unlike natural fibers such as cotton, wool, silk, and jute that come from plants and animals, synthetic fibers are entirely manufactured by humans to improve upon the properties of natural fibers.

The term "synthetic" comes from "synthesis," meaning "to make." Scientists developed synthetic fibers through extensive research to create materials that are stronger, more durable, and often less expensive than natural alternatives.

What Are Polymers and Monomers?

Understanding synthetic fibers requires knowledge of two key terms:

• Monomer: A simple chemical unit or molecule. The word comes from Greek: "mono" (one) + "mer" (unit).
• Polymer: A large molecule formed by joining many monomers together in a long chain. From Greek: "poly" (many) + "mer" (unit).

For example, glucose molecules (monomers) join together to form cellulose (polymer) in cotton fibers. Similarly, synthetic fibers are polymers made by joining simple chemical molecules through a process called polymerization.

Types and Examples of Synthetic Fibers

1. Rayon (Artificial Silk)

Manufacturing Process:

• Pure cotton or cellulose is soaked in 30% caustic soda solution for three hours
• The product is warmed with carbon disulfide to form cellulose xanthate
• This is dissolved in caustic soda to create viscose solution
• The viscose solution is passed through a spinneret into dilute sulfuric acid
• The viscose hardens into fine filaments that are wound onto spools

Characteristics:

• Cheaper than natural silk
• Highly absorbent, soft, and comfortable
• Easy to dye in various colors
• Drapes well

Uses:

• Blended with wool for carpets
• Mixed with cotton for bed sheets
• Long filaments used in reinforced automobile tires

2. Nylon

Nylon was the first fully synthetic fiber, developed in 1931 from coal, water, and air without using any natural raw material. The name comes from NY (New York) + LON (London), representing the collaborative effort between American and British scientists.

Manufacturing:

• Prepared by polymerization of amide molecules
• Amide molecules are obtained from petroleum products through complex chemical processes
• Forms long chains of polyamide molecules

Characteristics:

• Strong, elastic, and light
• Lustrous appearance (silk-like)
• Water-resistant
• Easy to wash

Uses:

• Clothing and fabric for shirts, dresses
• Parachutes (extensively used during World War II)
• Women's stockings (became extremely popular in 1939)
• Ropes for rock climbing and fishing nets
• Toothbrushes, combs, zip fasteners, hooks
• Tire cords and tennis racquet strings
• Machine parts like washers and pulleys

Historical Note: When nylon stockings were introduced in 1939, they became an instant hit. However, during World War II, production was diverted to making parachutes. After the war ended in 1945, demand was so high that women waited in long queues for hours, and a black market developed.

3. Polyester

Polyester fabrics are formed when alcohol reacts with organic acids (like acetic acid or phthalic acid) to create esters, which are then polymerized.

Terylene (Terene/Dacron)

Manufacturing:

• Polymerization of phthalic acid and ethylene glycol molecules
• Can be drawn into very fine fibers

Characteristics:

• Does not wrinkle easily
• Remains crisp
• Easy to wash
• Superior properties to nylon

Uses:

• Dress materials: shirts, trousers, sarees (sold as polycot, terrycot, polywool)
• Sails for sailing boats
• Fire hoses and conveyor belts

Note: Polycot = Polyester + Cotton blend; Polywool = Polyester + Wool blend

PET (Polyethylene Terephthalate)

Manufacturing:

• Polymerization of ethene terephthalate
• Easily drawn into fine filaments

Uses:

• Synthetic clothes with permanent creases
• Bottles for soft drinks, oils, and food packaging
• Magnetic tapes for audio and video cassettes

4. Acrylic

Acrylic is often called artificial wool because it resembles natural wool in appearance and warmth.

Manufacturing:

• Polymerization of acrylonitrile molecules
• Obtained from petroleum products through complex chemical processes

Characteristics:

• Very light and soft like wool
• Resistant to weathering
• Available in various colors
• Much cheaper than natural wool

Uses:

• Hand-knit sweaters and yarn
• Blankets and shawls (lightweight and warm)
• More affordable alternative to woolen products

5. Other Synthetic Fibers

Koroseal

• High polymer of vinyl chloride
• Waterproof and airproof
• Used for coating fabrics to make them waterproof
• Used in raincoats and bathroom curtains

How Synthetic Fibers Are Manufactured

General Manufacturing Process

1. Raw Material Extraction:
   • Petroleum products are processed to obtain petrochemicals
   • These include ethene, propene, benzene, toluene, etc.

2. Monomer Formation:
   • Raw materials are converted into suitable monomers through chemical processes
   • Examples: amide molecules for nylon, ester molecules for polyester

3. Polymerization:
   • Large numbers of monomers are joined together under specific physical and chemical conditions
   • Forms long polymer chains or cross-linked structures

4. Fiber Formation:
   • Molten polymer is passed through a spinneret (a device with tiny holes)
   • Forms thin filaments that solidify
   • Filaments are wound onto spools

5. Processing:
   • Fibers may be stretched, twisted, or treated
   • Can be dyed, blended with other fibers, or woven into fabrics

Plasticity and Polymerization

Plasticity is the property by which a substance can be molded into various shapes. Natural fiber polymers are plastic in nature, meaning they can be molded and shaped.

Chemists learned to replicate this process by combining simple molecules (monomers) into long chains (polymers) to create artificial fibers. This process is called polymerization.

Properties of Synthetic Fibers

Common Characteristics

Synthetic fibers generally share these properties:

✓ Heat-sensitive - Melt at high temperatures
✓ Resistant to moisture - Low water absorbency
✓ Resistant to insects, fungi, and rot
✓ Electrostatic - Generate static electricity
✓ Flame resistant (varies by type)
✓ Lightweight yet strong
✓ High density and tensile strength
✓ Prone to pilling (fabric balling)

Advantages of Synthetic Fibers

1. High Luster and Appearance

• Shiny, attractive appearance
• Do not yellow with age
• Maintain color vibrancy

2. Dimensional Stability

• Do not shrink when washed
• Retain original shape and size

3. Low Maintenance

• Need little or no ironing
• Wrinkle-resistant (especially polyester)
• Quick-drying

4. Durability

• Last longer than natural fibers
• Resistant to wear and tear
• High tensile strength (nylon is stronger than steel wire of same thickness)

5. Easy Care

• Simple to clean
• Dry quickly after washing
• Resistant to stains

6. Cost-Effective

• Less expensive than natural fibers
• More affordable clothing options
• Economical for various applications

7. Versatility

• Can be blended with natural fibers
• Available in numerous textures and finishes
• Suitable for diverse applications

Disadvantages of Synthetic Fibers

1. Fire Hazard

• Melt and burn easily at high temperatures
• Form small sticky beads when burning
• Molten fiber sticks to skin, causing severe burns
• Safety Warning: Never wear synthetic clothes while working in laboratories or near fire in kitchens

2. Poor Moisture Absorption

• Do not absorb sweat effectively
• Uncomfortable in summer or rainy seasons
• Can cause skin irritation and stickiness
• Solution: Blend with natural fibers like cotton or wool

3. Static Electricity

• Get electrically charged in dry weather
• Cause sparks (visible in synthetic blankets at night)
• Can cause skin problems in sensitive individuals
• Clothing clings to body

4. Environmental Concerns

• Not biodegradable
• Cause significant pollution
• Take several years to decompose
• Burning releases poisonous fumes
• Not eco-friendly

5. Limited Breathability

• Do not allow air circulation
• Can trap heat and moisture
• Less comfortable for prolonged wear

Plastics: Synthetic Polymer Materials

What Are Plastics?

Plastics are polymers with long carbon chains that can be easily molded into various shapes. The property of being moldable is called plasticity, and the materials themselves are called plastics.

Types of Plastics

1. Thermoplastics

Plastics that can be repeatedly softened by heating and reshaped.

Characteristics:

• Linear arrangement of monomers
• Can be reused and remolded
• Soften when heated
• Harden when cooled

Examples:

• Polyethene (Polythene)
• Polypropene
• Polyvinyl Chloride (PVC)
• Polystyrene
• Nylon
• Teflon

2. Thermosetting Plastics

Plastics that cannot be remolded once set.

Characteristics:

• Cross-linked arrangement of monomers
• Permanent molding
• Cannot be softened by reheating
• One-time use for shaping

Examples:

• Bakelite
• Urea formaldehyde
• Polyurethane
• Melamine

Uses of Thermosetting Plastics:

• Radio, television, and telephone cabinets
• Water tanks and pipes
• Electric switches
• Dinner sets and cups

Common Plastics and Their Uses

1. Polyethene (Polythene)

Manufacturing:

• Polymerization of ethene gas (CH₂=CH₂)
• Petroleum product

Properties:

• Insoluble in solvents
• Not attacked by strong chemicals
• Not biodegradable

Uses:

• Thin films for carry bags
• Adhesive tapes
• Kitchen and laboratory ware (cups, bottles)
• Insulation for electric wires
• Anti-corrosion coating on iron/copper articles

2. Polypropene

Manufacturing:

• Polymerization of propene gas (CH₃-CH=CH₂)

Uses:

• Ropes, packaging materials, containers
• Synthetic carpets
• Automobile battery casings
• Collapsible toys

3. Polyvinyl Chloride (PVC)

Manufacturing:

• Polymerization of vinyl chloride molecules

Uses:

• Handbags and raincoats
• Decorative vinyl flooring
• Shoe soles
• Gramophone records
• Water pipes, tanks, and sanitary fittings
• Superior insulation for electric wires

4. Teflon (Polytetrafluoroethene)

Manufacturing:

• Polymerization of tetrafluoroethene molecules

Properties:

• Unaffected by heat and chemicals
• Anti-stick properties

Uses:

• Non-stick coating for cookware (frying pans, baking utensils)
• Lubricant for machine parts where oil cannot be applied

5. Polystyrene

Properties:

• Lighter than polyethene
• Forms lightweight foam when air is blown through molten polystyrene
• Excellent insulating and packaging material

Uses:

• Insulating refrigerators and cold stores
• Ice box containers
• Packaging expensive items (cell phones, TVs)
• Car dashboard and aircraft parts
• Computer parts, circuit boards, appliances
• Thermocol (disposable cups and packaging)

Characteristics of Plastics

General Properties

✓ Non-reactive - Do not corrode easily
✓ Lightweight - Easy to transport and handle
✓ Strong - High tensile strength
✓ Durable - Long-lasting
✓ Poor conductors - Do not conduct heat or electricity
✓ Weather-resistant - Not biodegradable
✓ Moldable - Can be shaped into any form
✓ Versatile appearance - Can be transparent or opaque, any color

Why Plastics Are Widely Used

1. Non-Reactive:
   • Do not rust like metals
   • Resist water and air exposure
   • Suitable for storing chemicals and various materials

2. Light, Strong, and Durable:
   • Easy to handle and transport
   • Can be molded into different shapes and sizes
   • Generally cheaper than metals
   • Widely used in industry and households

3. Poor Conductors:
   • Ideal for electrical wire coverings
   • Safe handles for screwdrivers and tools
   • Insulating properties protect against electric shock

4. High Tensile Strength:
   • Synthetic plastic thread can withstand more weight than cotton of same thickness
   • Suitable for structural applications

5. Weather Resistance:
   • Not biodegradable (though this is also a disadvantage)
   • Do not weather like natural materials

6. Appearance:
   • Can be made transparent like glass
   • Available in any desired color or texture
   • Suitable for decorative and functional products

Plastics in Various Industries

Healthcare Industry

• Surgical instruments
• Syringes and medical containers
• Prosthetics
• Pill bottles and packaging

Cookware and Utensils

• Melamine: Fire-resistant plastic coating
• Heat-resistant containers
• Microwave-safe dishes
• Storage containers

Construction

• PVC pipes and fittings
• Insulation materials
• Window frames
• Flooring

Packaging

• PET bottles for beverages
• Food containers
• Protective packaging for electronics
• Plastic films and wraps

Environmental Impact of Synthetic Fibers and Plastics

Major Environmental Concerns

1. Non-Biodegradability

Problem:

• Synthetic materials do not decompose naturally
• Take several years (sometimes centuries) to degrade
• Accumulate in environment

Impact:

• Soil pollution: Plastic in compost prevents water seepage, affecting plant growth and groundwater recharge
• Ocean pollution: Plastic waste harms marine life
• Landfill accumulation: Takes up valuable space

Comparison of Degradation Times:

Material Type	Nature	Approximate Degradation Time
Vegetable/fruit peels	Biodegradable	1-2 weeks
Paper	Biodegradable	10-30 days
Cotton cloth	Biodegradable	2-5 months
Woollens	Biodegradable	About 1 year
Wood	Biodegradable	10-15 years
Plastics	Non-biodegradable	Several years (varies by type)
Metal cans	Non-biodegradable	100-500 years

2. Harm to Wildlife

• Stray animals eat plastic bags from garbage, causing digestive blockages and death
• Marine animals mistake plastic for food
• Birds and fish get entangled in plastic waste

3. Drainage and Water System Blockage

• Plastic bags clog city drainage systems
• Block small freshwater drains
• Cause flooding and water accumulation
• Create breeding grounds for disease-carrying insects

4. Air Pollution

• Burning plastics releases poisonous fumes
• Incomplete combustion produces toxic gases
• Contributes to air quality degradation
• Health hazards from inhaling plastic fumes

5. Resource Depletion

• Made from petroleum products (non-renewable resources)
• Continuous production depletes fossil fuel reserves
• Energy-intensive manufacturing process

Managing Plastic Waste: The 4 R's

1. Reduce

Minimize plastic use:

• Avoid disposable plastic bags
• Use reusable shopping bags (cotton, jute)
• Choose products with minimal plastic packaging
• Opt for alternatives whenever possible

2. Reuse

Extend the life of plastic items:

• Use plastic containers multiple times
• Repurpose plastic bottles for storage
• Donate usable plastic items instead of discarding
• Creative reuse in crafts and projects

3. Recycle

Process plastic waste for new products:

• Separate recyclable plastics
• Use designated recycling bins (green bin for biodegradable, blue bin for recyclable)
• Support recycling programs
• Choose products made from recycled materials

Recycling Codes:

Plastics are marked with numbers 1-7 to indicate type:

Number	Type	Common Uses
1	PETE (Polyethylene Terephthalate)	Soft drink bottles, water bottles
2	HDPE (High-Density Polyethylene)	Milk jugs, detergent bottles
3	V/PVC (Polyvinyl Chloride)	Pipes, window frames
4	LDPE (Low-Density Polyethylene)	Plastic bags, squeeze bottles
5	PP (Polypropylene)	Food containers, bottle caps
6	PS (Polystyrene)	Disposable cups, packaging
7	OTHER	Mixed plastics, BPA products

Principle: The smaller the number, the easier it is to recycle.

4. Recover

Energy recovery from non-recyclable plastics:

• Waste-to-energy processes
• Proper disposal in designated facilities
• Scientific incineration with emission controls

Additional Solutions

Biodegradable Plastics:

• Scientists are developing plastics that decompose naturally
• Photodegradable plastics break down in sunlight
• Bio-based plastics from renewable sources

Policy Measures:

• Ban on single-use plastics in many regions
• Plastic bag fees and charges
• Extended producer responsibility programs

How to Care for Garments Made of Synthetic Fibers

Washing Guidelines

Do:

• Use cold or lukewarm water (synthetic fibers are heat-sensitive)
• Use mild detergents
• Separate colors (dark and light)
• Turn garments inside out to protect surface
• Read care labels carefully

Don't:

• Use hot water (can damage or melt fibers)
• Use harsh chemicals or bleach
• Overload washing machine
• Wring excessively (can stretch fibers)

Drying Tips

• Air dry whenever possible
• Avoid direct sunlight (can fade colors)
• Use low heat settings if using a dryer
• Remove promptly to prevent wrinkles
• Hang or lay flat to maintain shape

Ironing Precautions

Important: Synthetic fibers melt at high temperatures!

• Use the lowest temperature setting
• Place a thin cloth between iron and garment
• Test on an inconspicuous area first
• Many synthetics don't require ironing
• Steam carefully from a distance

Storage

• Store in cool, dry places
• Avoid plastic bags (can trap moisture)
• Use breathable garment bags
• Fold knits, hang wovens
• Keep away from heat sources

Stain Removal

• Treat stains immediately
• Blot, don't rub
• Use appropriate stain removers for synthetic fabrics
• Test cleaners on hidden areas first
• Avoid harsh scrubbing

Special Considerations

Blended Fabrics:

• Follow care instructions for the more delicate fiber
• Polycot and polywool may have specific requirements
• Balance care between natural and synthetic components

Static Electricity:

• Use fabric softener in final rinse
• Anti-static spray for stubborn static
• Choose natural fiber undergarments in dry climates

Formulas

Concept	Representation	Explanation
Monomer	Simple unit (M)	Single chemical molecule; building block of polymers
Polymer	M-M-M-M-M-M...	Many monomers joined in long chains
Polymerization	n(Monomer) → Polymer	Chemical process joining monomers to form polymers
Cellulose	(C₆H₁₀O₅)ₙ	Natural polymer; glucose monomers in cotton
Ethene	CH₂=CH₂	Monomer for polyethene (plastic bags)
Propene	CH₃-CH=CH₂	Monomer for polypropene (ropes, containers)
Polyamide	Amide chains	Nylon structure; formed from amide monomers
Ester Formation	Alcohol + Acid → Ester	Basic reaction for polyester fibers
PET	Polyethylene Terephthalate	Polymer for bottles and synthetic clothes
Plasticity	Property of moldability	Ability to be shaped into various forms

Important Definitions

Synthetic Fiber: Man-made fiber prepared from petrochemicals through polymerization, designed to improve upon natural fibers.

Natural Fiber: Fiber obtained from natural sources like plants (cotton, jute) or animals (wool, silk).

Petrochemicals: Raw materials derived from petroleum used in manufacturing synthetic fibers and plastics.

Biodegradable: Materials that decompose naturally through bacterial action (e.g., food waste, paper, cotton).

Non-biodegradable: Materials that do not decompose naturally and persist in the environment (e.g., plastics, synthetic fibers, metal cans).

Thermoplastic: Plastic that softens when heated and can be remolded repeatedly (e.g., PVC, polyethene).

Thermosetting Plastic: Plastic that cannot be remolded once set, due to cross-linked polymer structure (e.g., bakelite, melamine).

Rayon: First semi-synthetic fiber made from wood pulp; also called artificial silk.

Nylon: First fully synthetic fiber made from coal, water, and air without natural raw materials.

Acrylic: Synthetic fiber similar to wool; often called artificial wool.

PET: Polyethylene terephthalate; common polyester used for bottles and fabrics.

Comparison Tables

Natural vs. Synthetic Fibers

Feature	Natural Fibers	Synthetic Fibers
Source	Plants and animals	Petrochemicals
Cost	Generally expensive	Relatively cheap
Weight	Heavier	Lighter
Strength	Lower tensile strength	High tensile strength
Water Absorption	High (absorbs sweat)	Low (doesn't absorb well)
Heat Conductivity	Good (except cotton/jute)	Poor conductors
Durability	Less durable	More durable
Biodegradability	Biodegradable	Non-biodegradable
Comfort	More comfortable	Less comfortable (doesn't breathe)
Examples	Cotton, wool, silk, jute	Nylon, polyester, acrylic

Thermoplastic vs. Thermosetting Plastic

Property	Thermoplastic	Thermosetting Plastic
Structure	Linear polymer chains	Cross-linked polymer chains
Remolding	Can be remolded	Cannot be remolded
Heating Effect	Softens when heated	Does not soften when heated
Reusability	Can be reused	One-time molding only
Examples	Polyethene, PVC, Polystyrene, Nylon	Bakelite, Melamine, Urea formaldehyde
Common Uses	Bottles, bags, wires, containers	Switches, handles, dinner sets, cabinets

Summary Points

• Synthetic fibers are man-made from petrochemicals through polymerization
• Main types: Rayon, Nylon, Polyester (Terylene, PET), Acrylic
• Nylon was the first fully synthetic fiber (1931)
• Rayon is called artificial silk and is semi-synthetic
• Advantages: Durable, strong, cheap, wrinkle-resistant, quick-drying
• Disadvantages: Fire hazard, poor sweat absorption, non-biodegradable, static electricity
• Plastics are moldable polymers classified as thermoplastic or thermosetting
• Environmental impact: Non-biodegradable, causes pollution, harms wildlife
• Management: Follow the 4 R's—Reduce, Reuse, Recycle, Recover
• Safety: Never wear synthetic clothes near fire or in laboratories

Conclusion

Synthetic fibers and plastics have revolutionized modern life by providing affordable, durable, and versatile materials for clothing, packaging, and countless applications. While they offer significant advantages over natural materials in terms of cost, strength, and maintenance, they also present serious environmental challenges due to their non-biodegradable nature.