UPSC Prelims 2022 Q46: Science & Technology – Materials & Engineering
With reference to polyethylene terephthalate, the use of which is so widespread in our daily
lives, consider the following statements:
1. Its fibres can be blended with wool and cotton fibres to reinforce their properties.
2. Containers made of it can be used to store any alcoholic beverage.
3. Bottles made of it can be recycled into other products.
4. Articles made of it can be easily disposed of by incineration without causing greenhouse gas
emissions.
Which of the statements given above are correct?
- (a) 1 and 3
- (b) 2 and 4
- (c) 1 and 4
- (d) 2 and 3
Answer: (a) 1 and 3
Explanation
Polyethylene terephthalate (PET)
| Statement | Verdict | Fact |
|---|---|---|
| 1. PET fibres blend with wool and cotton | Correct | PET is polyester; poly-cotton and poly-wool blends add strength and crease resistance |
| 2. PET containers can store any alcoholic beverage | Incorrect | PET is permeable to gases and can leach compounds; it is unsuitable for long storage of spirits and wine |
| 3. PET bottles can be recycled | Correct | Recycled rPET becomes fibre, sheets, strapping and new bottles |
| 4. PET can be incinerated without greenhouse gases | Incorrect | Burning PET releases carbon dioxide and other pollutants |
PET in daily life:
| Use | Example |
|---|---|
| Packaging | Water and soft-drink bottles |
| Textiles | Polyester clothing and fleece |
| Films | Food trays and packaging film |
Answer: (a) 1 and 3.
Why each option is right or wrong
- (a) CORRECT. PET is polyester fibre used in blends, and PET bottles are widely recycled.
- (b) Incorrect. PET is not fit for every alcoholic drink, and burning it does emit CO₂.
- (c) Incorrect. Statement 4 is false; incineration of any carbon-based plastic releases CO₂.
- (d) Incorrect. The word 'any' makes statement 2 false; PET is unsuitable for long storage of spirits.
Key point
PET = polyester: blends with cotton and wool, recyclable as rPET, but burning it emits CO₂.
Remember
PET = polyester; blendable and recyclable, but burning it emits CO₂.
Common mistakes
- Missing the absolute word 'any' in statement 2, which makes it false.
- Believing incineration of plastic can be greenhouse-gas free; burning carbon always yields CO₂.
- Not linking PET to polyester fibre used in textile blends.
Exam tip
Absolute words like 'any', 'all' and 'without' usually signal a false statement in UPSC science questions.
Sources
- NCERT Class VIII — Science, Ch 3 (Synthetic Fibres and Plastics)
- Central Pollution Control Board — Plastic Waste Management guidance