Question
Compare natural and synthetic fibres in terms of their properties, advantages, and disadvantages.
Solution — Step by Step
Natural fibres are obtained from plants (cellulose-based) or animals (protein-based). Examples: cotton, jute, silk, wool.
Synthetic fibres are manufactured by humans through chemical processing of petrochemicals or other raw materials. They are polymers made by condensation or addition polymerisation. Examples: nylon, polyester, acrylic, rayon (semi-synthetic).
Rayon is a special case — it is made from wood pulp (natural source) but processed chemically. It is called a semi-synthetic fibre.
| Property | Natural Fibres | Synthetic Fibres |
|---|---|---|
| Source | Plants/animals | Petroleum/chemicals |
| Moisture absorption | High (hygroscopic) | Low |
| Heat resistance | Moderate to high | Low to moderate (melt on heating) |
| Strength | Moderate | Generally higher |
| Elasticity | Lower (except wool) | Higher |
| Biodegradability | Yes | No (or very slow) |
| Cost | Generally higher | Generally lower |
| Texture | Soft, natural feel | Can be rough; varies |
| Shrinkage | Cotton shrinks, wool felts | Mostly resistant to shrinkage |
- Breathable — high moisture absorption keeps the body cool (cotton in Indian summers)
- Biodegradable — decompose naturally, reducing environmental burden
- Skin-friendly — less allergic response compared to some synthetics
- Heat-resistant — cotton and wool don’t melt; safer near flames (though they can burn)
- Comfortable texture — preferred for daily wear and medical use
- Expensive — require agricultural land, water, labour
- Wrinkle easily — cotton needs ironing; silk requires careful handling
- Susceptible to pests and mould — wool is eaten by moths; cotton can be attacked by fungi
- Variable quality — depends on growing conditions, season
- Limited supply — land and water resources are finite
Advantages:
- Strong and durable — nylon has very high tensile strength; polyester resists stretching
- Cheap to produce — mass production keeps cost low
- Wrinkle-resistant — polyester shirts need minimal ironing
- Lightweight — ideal for outdoor and sports clothing
- Versatile — can be engineered for specific properties (flame-retardant, waterproof)
Disadvantages:
- Non-biodegradable — persist in environment for hundreds of years; microplastic pollution
- Poor moisture absorption — uncomfortable in hot/humid conditions; traps sweat
- Melt on heating — synthetic clothes can catch fire and melt onto skin — dangerous
- Skin irritation — some people have allergic reactions to acrylic or polyester
- Environmental cost — derived from petroleum, a non-renewable resource
Why This Works
The differences between natural and synthetic fibres come down to their molecular structure and source material:
Natural fibres are biopolymers — cellulose (plant) or proteins (animal). Cellulose chains have many -OH groups that hydrogen-bond with water, giving cotton its absorbency. Protein fibres like wool have complex coiled structures (alpha helices) that give them elasticity and warmth.
Synthetic fibres are designed polymers — nylon is a polyamide with strong inter-chain hydrogen bonds (very strong), polyester has ester linkages, acrylic has CN groups. Their regular, tightly packed chains resist moisture absorption and mechanical deformation.
Alternative Method — Specific Fibre Examples
To make your answer more specific and score higher in board exams:
| Fibre | Type | Key Properties |
|---|---|---|
| Cotton | Natural (plant) | Absorbent, breathable, burns cleanly |
| Silk | Natural (animal) | Lustrous, smooth, expensive |
| Wool | Natural (animal) | Warm, elastic, felts with heat+moisture |
| Nylon | Synthetic | Strongest, elastic, melts at ~180°C |
| Polyester | Synthetic | Wrinkle-resistant, strong, cheap |
| Acrylic | Synthetic | Wool-like feel, cheap, lightweight |
| Rayon | Semi-synthetic | Silk-like, absorbent, biodegradable |
CBSE exams (Class 8 Science) frequently ask: “Why should we avoid wearing synthetic clothes while working in a kitchen or near fire?” Answer: Synthetic fibres melt on heating and can stick to skin, causing severe burns. Natural fibres like cotton catch fire but do not melt — safer near heat sources.
Common Mistake
Students often say “synthetic fibres are always stronger than natural fibres.” This is an oversimplification. Silk, for example, has very high tensile strength — comparable to some synthetics. Also, cotton in its natural state is weaker than nylon, but treated cotton composites can be very strong. Always qualify your comparison with specific examples.