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Subjects · Leaving Cert Engineering

Leaving Cert Engineering: Plastics, elastomers & composites

How often Plastics, elastomers & composites comes up on the Engineering papers, every year it was asked, and questions to try.

HL Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

OL Asked on 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

June 2028 is the first exam on the new Engineering course. These come from the 2016–2025 papers, so read them as a guide.

Plastics, elastomers & composites, Higher Level(7 marks)

Quick ones on Plastics, elastomers & composites.

(a)Why can a thermoset not be softened and remoulded by heating?
  1. Its chains are held only by weak forces
  2. Its chains are joined by strong cross-links
  3. It has no polymer chains
(b)Plastic used as the coating on non-stick frying pans?
  1. Urea formaldehyde
  2. Polystyrene
  3. PTFE
(c)A bent acrylic strip goes flat again when reheated. This property is called?
  1. Elastic memory
  2. Work hardening
  3. Elasticity
Show the answers

(a) Its chains are joined by strong cross-links

(b) PTFE

(c) Elastic memory

Your turn: Higher Level questions on Plastics, elastomers & composites.

Higher Level

Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q7
2024Q1(h), Q7
2023Q1(d), Q7
2022Q7
2021Q1(m), Q7
2019Q1(a), Q1(f), Q6
2018Q1(j), Q6
2017Q1(h), Q6
2016Q1(g), Q6

Links open the State Examinations Commission’s paper for that year.

More Plastics, elastomers & composites questions

Plastics, elastomers & composites, 3 marks

Why is nylon often used for small gears and bushes?

  1. It conducts electricity well
  2. It is a thermoset that never softens
  3. Low friction, tough and wear resistant
Show the answer

Low friction, tough and wear resistant

Nylon is a tough thermoplastic with a naturally low coefficient of friction, so it runs quietly with little lubrication. It is an insulator.

Plastics, elastomers & composites, 3 marks

Degree of polymerisation means?

  1. The percentage of filler in a plastic
  2. The number of monomer units in a polymer chain
  3. The temperature at which a polymer melts
Show the answer

The number of monomer units in a polymer chain

Longer chains (higher degree of polymerisation) tangle more, giving higher strength and melting point. It is a count of repeating units.

Plastics, elastomers & composites, 3 marks

Forces between the chains of a thermoplastic?

  1. Weak intermolecular (van der Waals) forces
  2. Strong covalent cross-links between chains
  3. Metallic bonds with free electrons
Show the answer

Weak intermolecular (van der Waals) forces

Heat overcomes these weak forces, so the chains slide past each other and the plastic softens. That is why thermoplastics can be reheated and remoulded.

Ordinary Level

Asked on 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q5
2024Q5
2023Q5
2022Q5
2021Q5
2019Q5
2018Q5
2017Q5
2016Q5

Links open the State Examinations Commission’s paper for that year.

More Plastics, elastomers & composites questions

Plastics, elastomers & composites, 2 marks

What is a thermoplastic?

  1. Plastic that sets permanently when first heated
  2. Plastic reinforced with glass fibres
  3. Plastic that softens every time it is heated
Show the answer

Plastic that softens every time it is heated

Thermoplastics like acrylic, PVC and nylon have long chains with weak bonds between them, so they soften on heating and can be reshaped and recycled.

Plastics, elastomers & composites, 2 marks

What is fibreglass (GRP)?

  1. Rubber reinforced with thin steel wire
  2. Glass fibres set in a polyester or epoxy resin
  3. Molten glass blown into a mould and cooled
Show the answer

Glass fibres set in a polyester or epoxy resin

GRP is a composite: the fibres give strength, the resin binds and shapes them. It is light, strong and rot-proof, used for boat hulls and car panels.

Plastics, elastomers & composites, 2 marks

What is a thermosetting plastic?

  1. Plastic that sets permanently and will not soften again
  2. Plastic that softens again each time it is reheated
  3. A rubber that stretches and springs back into shape
Show the answer

Plastic that sets permanently and will not soften again

Cross-links form when a thermoset sets, locking the chains. Reheating chars it instead of softening it, so it suits hot or electrical items like pan handles and plugs.

Other Engineering topics

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