Synthetic Fibres and Plastics

What you'll learn

Synthetic fibres: man-made fibres produced from chemical substances (petrochemicals/raw materials derived from petroleum).
Made of large molecules called polymers (long chains of repeating smaller units called monomers).
Also called artificial fibres or man-made fibres.

Raw materials: coal, petroleum, water, air — processed chemically → synthetic polymer → extruded as fibre.

First fully synthetic fibre (introduced in 1935 by DuPont, USA).
Polymer name: polyamide (PA).
Properties:
- Very strong, elastic, lightweight.
- Smooth and lustrous (silk-like appearance).
- Quick-drying; low moisture absorption.
- High melting point; resistant to chemicals.
Uses: stockings and tights, toothbrush bristles, parachutes, climbing ropes, sleeping bags, seat belts, sports equipment, surgical thread.

Polymer: polyethylene terephthalate (PET) — most common; also polybutylene terephthalate (PBT).
Properties:
- Wrinkle-resistant: fibres spring back after creasing.
- Durable — does not wear out quickly.
- Low moisture absorption — dries quickly.
- Can be blended with cotton or wool to improve properties.
Uses: clothing (fleece jackets, sportswear), bottles (PET), ropes, sails, bedsheets, carpets, conveyor belts.
Terylene: brand name for polyester yarn (used in clothes).

Resembles wool — warm, soft, bulky.
Lighter than wool; less expensive; easier to wash (machine washable).
Uses: sweaters, blankets, carpets, socks, fleece.
Disadvantage: less breathable than wool; melts if burned (not self-extinguishing like wool).

Property	Natural (cotton, wool, silk)	Synthetic (nylon, polyester, acrylic)
Source	Plants / animals	Petroleum chemicals
Moisture absorption	High	Low
Durability	Moderate	High
Comfort/breathability	Better	Less
Wrinkle resistance	Lower	Higher
Cost	Usually higher	Usually lower
Biodegradable	Yes	No
Flammability	Burns, chars	Melts; may drip burning plastic

Safety concern: synthetic clothes melt when heated → stick to skin → dangerous. Keep away from open flames.

Plastic: a synthetic material that can be moulded into any shape when heated and retains that shape when cooled.

Types of plastics:

Type	Properties	Examples	Recyclable?
Thermoplastics	Soften on heating; can be remoulded; can be recycled	Polythene (PE), PVC, PET, polystyrene (PS)	Yes
Thermosetting plastics	Set permanently once formed; do NOT soften again on heating; cannot be recycled	Bakelite, melamine, urea-formaldehyde	No

Bakelite: first synthetic plastic (1907); poor conductor of heat and electricity → used in electrical switches, plugs.

Common plastics and uses:

Plastic	Abbr.	Common use
Polyethylene (low density)	LDPE	Plastic bags, bottles, packaging film
Polyethylene (high density)	HDPE	Pipes, containers, hard bottles
Polyvinyl chloride	PVC	Pipes, floor tiles, raincoats, cables
Polystyrene	PS	Foam cups, packaging foam (thermocol), food containers
Polypropylene	PP	Containers, furniture, textiles
PET	PET	Water bottles, polyester fibre

Problems:

Plastics are non-biodegradable — microorganisms cannot break them down; persist in environment for hundreds of years.
Microplastics: plastic degrades into tiny particles → found in oceans, soil, drinking water, and even in human blood.
Marine pollution: plastic bags and bottles kill marine animals (mistaken for food; entanglement).
Soil pollution: plastic in soil reduces fertility; blocks water penetration.
Clogged drains: plastic bags block drainage → flooding in cities.
Air pollution: burning plastics releases toxic gases (dioxins, HCl from PVC).

Solutions — 4Rs + more:

What is a synthetic fibre? From what raw material are most made?
Name three properties of nylon that make it useful for ropes and parachutes.
What is the difference between thermoplastics and thermosetting plastics? Give an example of each.
Why are plastics harmful to the environment? Name two specific problems.
What does 'non-biodegradable' mean? Why is this a problem for plastic waste?

Open the Practice tab for graded questions on Synthetic Fibres and Plastics.