What Are Synthetic Fibres, and Why Do We Need Them?
Cotton tears. Silk costs a fortune. Wool gets eaten by moths. Natural fibres have been around for thousands of years, but they come with serious limitations — and that’s exactly why chemists started making their own.
Synthetic fibres are man-made fibres produced by chemical processing of raw materials, mostly derived from petrochemicals (petroleum and natural gas). We stitch together small chemical units called monomers into long chains called polymers — and then spin those polymers into threads.
Think of it like this: natural fibres are already made by plants or animals. Synthetic fibres are built from scratch in a factory, monomer by monomer, which means we control the properties from the ground up. Want a fibre that doesn’t absorb water? We can make that. Flame-resistant? That too.
The same logic applies to plastics — polymer materials we can mould into any shape. A plastic chair, a water bottle, a phone case — all polymers, all synthetic.
This chapter has a high scoring weightage in Class 8 board exams, and the concepts here form the foundation you’ll need when polymers appear in Class 12 Chemistry. Let’s understand it properly.
Key Terms and Definitions
Monomer — The small, repeating chemical unit that links together to form a polymer. From Greek: mono (single) + meros (part). Example: ethylene (CH₂=CH₂) is the monomer for polythene.
Polymer — A large molecule made of many monomers joined in a chain. From Greek: poly (many) + meros (part). Most synthetic fibres and all plastics are polymers.
Polymerisation — The chemical reaction that joins monomers into a polymer chain.
Thermoplastic — A plastic that softens on heating and can be remoulded. Examples: Polythene, PVC, polystyrene.
Thermosetting plastic — A plastic that, once set hard, cannot be softened again by heating. Examples: Bakelite, melamine.
Biodegradable — Substances that can be broken down by bacteria or other living organisms. Natural fibres are biodegradable; most synthetic ones are not.
Non-biodegradable — Substances that do NOT break down naturally and persist in the environment for decades or centuries. This is the big environmental problem with synthetic fibres and plastics.
Types of Synthetic Fibres
1. Rayon (Artificial Silk)
Rayon is technically a semi-synthetic fibre — it comes from a natural source (wood pulp cellulose) but is heavily chemically processed. It was created to mimic silk at a fraction of the cost.
Properties: soft, shiny, absorbs moisture well, cheaper than silk. Uses: sarees, bed sheets, carpets.
CBSE often asks: “Is rayon natural or synthetic?” The correct answer is semi-synthetic or artificial silk — it comes from natural cellulose but requires extensive chemical processing. Don’t write “fully natural.”
2. Nylon
Nylon was the world’s first fully synthetic fibre, made entirely from coal, water, and air. It was introduced in 1935 and became famous as a material for stockings.
Properties: very strong, elastic, lustrous, resistant to chemicals, dries quickly. Uses: toothbrush bristles, ropes, parachutes, sleeping bags, socks, sportswear.
The strength of nylon is remarkable — a thin nylon rope can support tremendous weight. That’s why it’s used for climbing ropes and parachute cords where lives depend on it.
3. Polyester (PET — Polyethylene Terephthalate)
Polyester is the most widely produced synthetic fibre in the world. Your school uniform is almost certainly polyester or a polyester blend.
Properties: strong, wrinkle-resistant, holds shape well, dries quickly, doesn’t absorb water much. Uses: clothing (mixed with cotton as “polycot”), bottles (PET bottles), films, audio/video tapes.
Polycot = polyester + cotton blend. You get cotton’s breathability and polyester’s wrinkle resistance. Good compromise for uniform fabric.
Polywool = polyester + wool. Used in suiting fabric — keeps the drape of wool but costs less.
4. Acrylic (Artificial Wool)
Acrylic fibres mimic wool. They’re lighter and cheaper, and unlike real wool, they don’t get attacked by moths.
Properties: soft, warm, lightweight, retains colour well. Uses: sweaters, shawls, blankets, carpets.
Remember this for exams: Acrylic is to wool what rayon is to silk. Both are “artificial” versions of a more expensive natural fibre.
Types of Plastics
Thermoplastics
These can be melted and reshaped multiple times. The polymer chains are held together by weak forces, so heat breaks them apart and they can flow.
| Plastic | Common Use |
|---|---|
| Polythene (PE) | Carry bags, bottles, buckets |
| PVC (Polyvinyl chloride) | Pipes, raincoats, shoes |
| Polystyrene | Foam cups, packaging material |
| Teflon | Non-stick cookware coating |
Teflon deserves special mention. It has the lowest coefficient of friction of any known solid — almost nothing sticks to it. That’s why your dosas don’t stick on a non-stick pan.
Thermosetting Plastics
Once set, they cannot be remoulded. The polymer chains form cross-links that hold them permanently in shape.
Bakelite — Made from phenol and formaldehyde. Used in electrical switches, handles of pans, and the dark casings of old radios. It’s a poor conductor of electricity and heat — ideal for safety applications.
Melamine — Used in floor tiles, kitchenware, and fire-resistant fabrics. Melamine can withstand higher temperatures than most plastics. School dinner plates are often melamine.
A classic CBSE short-answer question: “Why is Bakelite used for making electrical switches?” Answer: Bakelite is a thermosetting plastic that is a poor conductor of electricity (electrical insulator) and does not soften on heating. It cannot be remoulded, which makes it stable in the switch.
Characteristics of Synthetic Fibres
Let’s compare systematically — this table format comes up in board exams:
| Property | Natural Fibres | Synthetic Fibres |
|---|---|---|
| Source | Plants/animals | Petrochemicals |
| Moisture absorption | High | Low |
| Wrinkle resistance | Low | High |
| Cost | Generally higher | Generally lower |
| Durability | Moderate | High |
| Biodegradability | Yes | No |
| Comfort in heat | Good | Less comfortable |
For warm, humid Indian summers, natural fibres (cotton) are more comfortable because they absorb sweat. Synthetic fibres trap heat and moisture. This is why your PE teacher wears cotton, not polyester!
Plastics and the Environment
This section is increasingly important for CBSE — environmental issues now carry dedicated marks.
The core problem: Most plastics are non-biodegradable. They don’t decompose for hundreds of years. A plastic bag you throw away today may still exist in 2500 CE.
How plastics harm the environment:
- They clog drains and cause flooding (major problem in Indian cities during monsoons).
- Animals, especially cows, eat plastic bags and die.
- Plastics in water bodies break into microplastics — tiny particles that enter the food chain and end up in fish, which we then eat.
- Burning plastics releases toxic gases including dioxins.
The 5Rs of Plastic Management:
- Refuse — don’t take what you don’t need
- Reduce — use less
- Reuse — use again before discarding
- Recycle — process into new material
- Recover — extract energy from waste
CBSE has asked: “Name two ways in which synthetic polymers have affected our environment.” This is a 2-mark question. Answer: (1) They are non-biodegradable and persist in the environment for centuries. (2) They release toxic gases when burned.
Solved Examples
Example 1 — Easy (CBSE Level)
Q: Why should we not wear synthetic clothes while working in the kitchen or while doing science experiments?
Solution:
Synthetic fibres are made of plastics and melt when they catch fire. Natural fibres like cotton will burn, but the fire spreads more slowly. When a synthetic fabric catches fire, it melts and sticks to the skin, causing severe burns that are harder to treat than a simple flame burn.
Cotton burns and chars away from the body. Synthetic cloth melts onto the body. That’s the critical difference.
Answer: Synthetic fibres catch fire easily, melt on burning, and stick to the body causing severe burns. Near heat sources (kitchen flame, Bunsen burner), cotton or wool is far safer.
Example 2 — Medium (CBSE, 3 marks)
Q: Explain why: (a) A nylon rope is used for rock climbing. (b) Teflon is used to coat non-stick pans. (c) Melamine is used in making fire-resistant fabrics.
Solution:
(a) Nylon rope for rock climbing: Nylon is the strongest synthetic fibre. It can bear very heavy loads without breaking and is also elastic — it has some stretch, which helps absorb sudden jerks (e.g., a climber’s fall). It’s also resistant to fungi and insects, unlike natural rope.
(b) Teflon on non-stick pans: Teflon (PTFE — polytetrafluoroethylene) is extremely slippery — nothing sticks to it. It’s also heat-resistant and chemically inert, so food doesn’t react with it. This makes it perfect for a coating where we want food to slide off easily.
(c) Melamine for fire-resistant fabrics: Melamine is a thermosetting plastic with a high melting point. It resists fire and doesn’t catch fire easily. Mixed with fibres, it makes fabrics that can withstand heat — used for firefighter uniforms and kitchen fabrics.
Example 3 — Hard (Application-Based, CBSE 5 marks or HOTS)
Q: Ravi has three bags: one cotton, one nylon, and one PET plastic bag. He wants to carry: (1) groceries from the market, (2) a heavy load of books. He also sees his grandmother wrapping her woollen sweater in a polythene bag. Comment on each situation — is the choice of material appropriate? Justify scientifically.
Solution:
(1) Cotton bag for groceries: Appropriate. Cotton is biodegradable, reusable, and strong enough for groceries. It doesn’t harm the environment. A plastic bag for occasional grocery use creates unnecessary non-biodegradable waste. Cotton is the responsible choice.
(2) Nylon bag for heavy books: Appropriate. Nylon has very high tensile strength — it can hold heavy loads without tearing. A cotton bag might tear under the weight of many books. Nylon’s strength makes it suitable for heavy loads.
(3) Grandmother’s sweater in polythene: Partially appropriate but not ideal. Polythene protects wool from moisture and moths. However, polythene traps moisture if any enters, and long-term storage in airtight plastic can damage wool fibres. Better alternatives exist (cedar-lined boxes, cotton covers). But the grandmother’s reasoning — protecting from insects — is scientifically valid since synthetic plastics aren’t eaten by moths.
Exam-Specific Tips
CBSE Class 8 Pattern:
- 1-mark questions: Name a thermosetting plastic. Name the monomer of polythene.
- 2-mark questions: Differences between thermoplastics and thermosetting plastics (2 points each).
- 3-mark questions: Properties and uses of nylon/polyester/rayon (usually 3 properties or 3 uses).
- 5-mark questions: Environmental impact of plastics with solutions, OR comparison of natural vs synthetic fibres.
- Diagram question: Structure of a polymer chain (rarely asked but know the concept).
The environmental impact section has grown in importance over the last 3 years of CBSE papers. Always connect plastic pollution to specific consequences: drain clogging, animal deaths, microplastic contamination.
For 3-mark questions on “differences,” always write in a proper table or point format. Examiners award marks per point — don’t write a paragraph.
Common Mistakes to Avoid
Mistake 1: Calling rayon “fully synthetic” Rayon is semi-synthetic — it comes from natural cellulose (wood pulp) but is chemically processed. The NCERT book itself calls it “artificial silk.” Write “semi-synthetic” or “artificial” — not “synthetic” or “natural.”
Mistake 2: Confusing thermoplastic and thermosetting plastic Many students mix these up. Memory trick: “Thermoplastic” — it stays plastic (mouldable) even after heating multiple times. “Thermosetting” — it sets permanently (like cement). Bakelite = thermosetting. Polythene = thermoplastic.
Mistake 3: Writing “synthetic fibres are bad” without nuance They have genuine advantages: cheaper, stronger, quick-drying, wrinkle-resistant. The problem is environmental persistence and flammability. In exams, show both sides unless the question specifically asks for disadvantages.
Mistake 4: Saying polythene is a fibre Polythene is a plastic, not a fibre. Polyester is the fibre. PET (polyethylene terephthalate) is used to make both polyester fibre AND plastic bottles — this dual-use confuses students.
Mistake 5: Forgetting that nylon was the FIRST fully synthetic fibre Rayon came before nylon chronologically, but rayon is semi-synthetic. Nylon (1935) was the first completely man-made fibre. This “first” fact appears in MCQs.
Practice Questions
Q1. Name the four main types of synthetic fibres studied in Class 8.
Rayon (semi-synthetic), Nylon, Polyester, and Acrylic are the four types. Remember: RNPA.
Q2. What is the difference between a monomer and a polymer? Give one example of each.
A monomer is a small single unit that can join with others to form a chain. Example: ethylene (CH₂=CH₂).
A polymer is a large molecule made of many monomers linked together. Example: polythene (formed from ethylene monomers).
Q3. Give two reasons why polythene bags should not be burned.
(1) Burning polythene releases toxic gases including carbon monoxide and dioxins, which are harmful to health. (2) Plastic ash and residue are also non-biodegradable and contaminate soil.
Q4. Why is Bakelite a better material than polythene for electrical switches?
Bakelite is a thermosetting plastic — it does not soften or melt on heating. Polythene is thermoplastic and would melt if the switch got hot. Bakelite is also an electrical insulator (does not conduct electricity), making it safe for switches.
Q5. A student says: “We should replace all natural fibres with synthetic fibres because synthetic fibres are stronger.” Do you agree? Why or why not?
No, this is not a good idea. While synthetic fibres are indeed stronger and more durable, they have serious drawbacks:
- They are non-biodegradable — they cause long-term environmental pollution.
- They are less comfortable in hot weather as they don’t absorb sweat well.
- They catch fire easily and melt on burning, posing a safety hazard.
- Natural fibres like cotton are biodegradable and renewable.
A balance is better — use each fibre where it performs best.
Q6. List two properties each that make nylon suitable for: (a) making ropes, (b) making toothbrush bristles.
(a) Ropes: High tensile strength (can hold heavy loads), elastic (absorbs sudden jerks).
(b) Toothbrush bristles: Hard and stiff (can clean teeth effectively), resistant to water and chemicals (doesn’t degrade in mouth conditions).
Q7. What is “polycot”? Why is it used for school uniforms?
Polycot is a blend of polyester and cotton fibres. It combines the strengths of both: cotton provides comfort and breathability (absorbs sweat), while polyester provides wrinkle resistance and durability. School uniforms need to look neat all day and withstand heavy daily wear — polycot achieves both goals.
Q8. The drain near Riya’s house gets blocked every monsoon. Her mother says “people keep throwing plastic bags.” Explain the science behind why plastic bags block drains and what we should do instead.
Plastic bags are non-biodegradable — they don’t decompose. When thrown into open drains, they accumulate and physically block water flow. Unlike paper or food waste, plastics don’t break down over time, so the blockage worsens with each bag added.
During monsoons, the rainwater cannot drain away, causing flooding on roads.
What we should do:
- Refuse single-use plastic bags — carry cloth or jute bags.
- Dispose of plastics in designated bins for recycling.
- Support local municipality drives to clean existing plastic waste from drains.
FAQs
Q: Is rayon natural or synthetic? Rayon is semi-synthetic. The raw material (cellulose from wood pulp) is natural, but it undergoes heavy chemical processing to produce the fibre. It cannot be called fully natural because of this chemical treatment, nor fully synthetic because the starting material is biological.
Q: What is the full form of PET? PET stands for Polyethylene Terephthalate. It’s the same polymer used to make polyester cloth AND plastic water bottles. When formed into fibres, it’s called polyester. When moulded into bottles, it’s called PET plastic.
Q: Why do synthetic clothes feel uncomfortable in summer? Synthetic fibres don’t absorb moisture well. When we sweat, cotton absorbs sweat and lets it evaporate, keeping us cool. Synthetic fibres trap the sweat against our skin, making us feel hot and sticky. This is a physical property of the polymer chains in synthetic fibres — they are hydrophobic (repel water).
Q: Can all plastics be recycled? No. Only thermoplastics can be melted and recycled into new products. Thermosetting plastics like Bakelite cannot be remelted — once they set, the cross-links are permanent. Recycling symbols on plastic packaging (1–7) indicate the type of plastic and whether it can be recycled.
Q: Why is nylon called the “wonder fibre”? Nylon earned this nickname because it was the first plastic that could be drawn into a fibre. It was stronger than steel by weight and could replace silk in stockings at a fraction of the cost. It was also the first material to be made entirely from coal, water, and air — a remarkable chemical achievement in 1935.
Q: Are all synthetic fibres made from petroleum? Most synthetic fibres (nylon, polyester, acrylic) are derived from petrochemicals. Rayon is an exception — it comes from plant cellulose. As petroleum resources deplete, chemists are developing bio-based synthetic fibres from agricultural waste.
Q: What are microplastics and why are they dangerous? Microplastics are plastic fragments smaller than 5 mm. They form when large plastic items break down over decades. Microplastics have been found in ocean water, fish tissue, drinking water, and even human blood. They can carry toxic chemicals and enter the food chain, with effects on human health still being studied.